Develop Reference

Divider line in RecyclerView behaves strange when expand and collapse items

When expanding and collapsing my Recyclerview items, divider lines drawn multiple times or overdrawn with items.
Also when expanding and collapsing views, dividers thickness is getting reduced.
My problem is divider line drawn each and every time I expand and collapse item in Recyclerview.
So is it possible to prevent divider line drawing if it already drawn?
While expanding an item, divider line will move according to the view.?
Below is my RecyclerView Decoration Class used for divider line,
public class SeparatorDecoration extends RecyclerView.ItemDecoration {
private final Paint mPaint;
/**
* Create a decoration that draws a line in the given color and width between the items in the view.
* #param context a context to access the resources.
* #param color the color of the separator to draw.
* #param heightDp the height of the separator in dp.
*/
public SeparatorDecoration(#NonNull Context context, #ColorInt int color,
#FloatRange(from = 0, fromInclusive = false) float heightDp) {
mPaint = new Paint();
mPaint.setColor(color);
final float thickness = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
heightDp, context.getResources().getDisplayMetrics());
mPaint.setStrokeWidth(thickness);
}
#Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) view.getLayoutParams();
// we want to retrieve the position in the list
final int position = params.getViewAdapterPosition();
// and add a separator to any view but the last one
if (position <state.getItemCount()) {
outRect.set(40, 0, 40, (int) mPaint.getStrokeWidth()); // left, top, right, bottom
} else {
outRect.setEmpty(); // 0, 0, 0, 0
}
}
#Override
public void onDrawOver(#NonNull Canvas c, #NonNull RecyclerView parent, #NonNull RecyclerView.State state) {
final int offset = (int) (mPaint.getStrokeWidth() / 2);
// this will iterate over every visible view
for (int i = 0; i < parent.getChildCount(); i++) {
// get the view
final View view = parent.getChildAt(i);
final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) view.getLayoutParams();
// get the position
final int position = params.getViewAdapterPosition();
// and finally draw the separator
if (position < parent.getChildCount()) {
final int ty = (int)(view.getTranslationY() + 0.5f);
final int top = view.getBottom() - params.bottomMargin + ty;
final int bottom = top + (int) mPaint.getStrokeWidth();
c.drawLine(view.getLeft(), view.getBottom() + offset, view.getRight(), view.getBottom() + offset, mPaint);
}
}
}
}
below is my RecyclerView Adapter class,
public class DisplayNotificationAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder>{
private Context context;
private List<NotificationDetails> notificationRecords;
private DeleteNotificationListener deleteNotificationListener;
private String TAG = DisplayNotificationAdapter.class.getSimpleName();
interface DeleteNotificationListener {
void updateNotificationList(List<NotificationDetails> details);
}
public DisplayNotificationAdapter(Context context, DeleteNotificationListener listener, List < NotificationDetails > notificationRecordsList) {
this.context = context;
this.deleteNotificationListener = listener;
this.notificationRecords = notificationRecordsList;
}
#NonNull
#Override
public RecyclerView.ViewHolder onCreateViewHolder (#NonNull ViewGroup parent, int viewType){
LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
AndroidLogger.log(5,TAG,"oncreate");
View listItem = layoutInflater.inflate(R.layout.display_notification_recycler_view_list_item, parent, false);
return new NotificationViewHolder(listItem);
}
#RequiresApi(api = Build.VERSION_CODES.N)
#Override
public void onBindViewHolder (#NonNull RecyclerView.ViewHolder holder,int position){
NotificationDetails notification = notificationRecords.get(position);
NotificationViewHolder viewHolder = (NotificationViewHolder) holder;
String currentDateString = DateFormat.getDateInstance().format(Long.parseLong(notification.getTimeStamp()));
String filePath=generateFilePath(notification.getFileName());
Bitmap myBitmap = BitmapFactory.decodeFile(filePath);
#SuppressLint("SimpleDateFormat")
DateFormat dateFormat = new SimpleDateFormat("hh:mm aa");
String time = dateFormat.format(Long.parseLong(notification.getTimeStamp()));
if (notification.isExpanded()) {
viewHolder.expandCollapseImageView.setImageDrawable(context.getDrawable(ImageDrawable.getDrawable("Up Arrow")));
expandView(viewHolder.notificationImageview);
}
else {
viewHolder.expandCollapseImageView.setImageDrawable(context.getDrawable(ImageDrawable.getDrawable("Down Arrow")));
collapseView(viewHolder.notificationImageview);
}
viewHolder.notificationImageview.setImageBitmap(myBitmap);
viewHolder.notificationTextView.setText(notification.getMessage());
viewHolder.notificationTimeTextView.setText(time);
Calendar now = Calendar.getInstance();
Calendar date = Calendar.getInstance();
date.setTimeInMillis(Long.parseLong(notification.getTimeStamp()));
viewHolder.expandCollapseImageView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(notification.isExpanded()) {
notification.setExpanded(false);
viewHolder.expandCollapseImageView.setImageDrawable(context.getDrawable(ImageDrawable.getDrawable("Down Arrow")));
viewHolder.notificationTextView.setMaxLines(1);
notifyItemChanged(position);
}
else {
notification.setExpanded(true);
viewHolder.expandCollapseImageView.setImageDrawable(context.getDrawable(ImageDrawable.getDrawable("Up Arrow")));
viewHolder.notificationTextView.setMaxLines(Integer.MAX_VALUE);
notifyItemChanged(position);
}
}
});
if (now.get(Calendar.DATE) == date.get(Calendar.DATE))
viewHolder.notificationDateTextView.setText("Today");
else if (now.get(Calendar.DATE) - date.get(Calendar.DATE) == 1)
viewHolder.notificationDateTextView.setText("Yesterday");
else
viewHolder.notificationDateTextView.setText(currentDateString);
if(notification.getTitle()==null)
viewHolder.notificationTitleTextView.setText("title");
else
viewHolder.notificationTitleTextView.setText(notification.getTitle());
}
private String generateFilePath(String fileName) {
File imageFileDirectory = context.getDir("image", Context.MODE_PRIVATE); //Creating an internal dir;
if (!imageFileDirectory.exists()) {
imageFileDirectory.mkdirs();
}
/*
* app server provide "U" file name after we set read status they provide same file name as "R"
*/
String createFilePath = imageFileDirectory + "/" + fileName;
return createFilePath;
}
public void removeSingleNotification ( int position){
DatabaseHelper databaseHelper = new DatabaseHelper(context);
databaseHelper.deleteSingleNotificationRecord(notificationRecords.get(position).getId());
notificationRecords.remove(position);
deleteNotificationListener.updateNotificationList(notificationRecords);
notifyDataSetChanged();
}
private void removeFromList (String id) {
for (NotificationDetails detail : notificationRecords) {
if (detail.getId().equalsIgnoreCase(id))
notificationRecords.remove(detail);
}
}
#Override
public int getItemCount () {
return notificationRecords.size();
}
public void expandView(final View v) {
int matchParentMeasureSpec = View.MeasureSpec.makeMeasureSpec(((View) v.getParent()).getWidth(), View.MeasureSpec.EXACTLY);
int wrapContentMeasureSpec = View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED);
v.measure(matchParentMeasureSpec, wrapContentMeasureSpec);
final int targetHeight = v.getMeasuredHeight();
// Older versions of android (pre API 21) cancel animations for views with a height of 0.
v.getLayoutParams().height = 1;
v.setVisibility(View.VISIBLE);
Animation a = new Animation()
{
#Override
protected void applyTransformation(float interpolatedTime, Transformation t) {
v.getLayoutParams().height = interpolatedTime == 1
? ViewGroup.LayoutParams.WRAP_CONTENT
: (int)(targetHeight * interpolatedTime);
v.requestLayout();
}
#Override
public boolean willChangeBounds() {
return true;
}
};
// Expansion speed of 1dp/ms
a.setDuration((int)(targetHeight / v.getContext().getResources().getDisplayMetrics().density));
v.startAnimation(a);
}
public void collapseView(final View v) {
//collapse(pos);
final int initialHeight = v.getMeasuredHeight();
Animation a = new Animation()
{
#Override
protected void applyTransformation(float interpolatedTime, Transformation t) {
if(interpolatedTime == 1){
v.setVisibility(View.GONE);
}else{
v.getLayoutParams().height = initialHeight - (int)(initialHeight * interpolatedTime);
v.requestLayout();
}
}
#Override
public boolean willChangeBounds() {
return true;
}
};
// Collapse speed of 1dp/ms
a.setDuration((int)(initialHeight / v.getContext().getResources().getDisplayMetrics().density));
v.startAnimation(a);
}
public static class NotificationViewHolder extends RecyclerView.ViewHolder {
private TextView notificationTextView, notificationDateTextView, notificationTimeTextView, notificationTitleTextView;
private ImageView notificationImageview,expandCollapseImageView;
private ConstraintLayout parent;
public NotificationViewHolder(#NonNull View itemView) {
super(itemView);
notificationTextView = itemView.findViewById(R.id.notification_text_view);
notificationDateTextView = itemView.findViewById(R.id.notification_date_text_view);
notificationTimeTextView = itemView.findViewById(R.id.notification_time_text_view);
notificationTitleTextView = itemView.findViewById(R.id.notification_title_text_view);
notificationImageview = itemView.findViewById(R.id.notification_image_view);
expandCollapseImageView = itemView.findViewById(R.id.expand_collapse_arrow);
parent = itemView.findViewById(R.id.notification_parent);
}
}
}
UPDATE
I doesn't able to solve this issue. So instead of using RecyclerView.ItemDecoration I have used a View inside layout like below,
<View
android:layout_width="match_parent"
android:layout_height="1dp"
android:id="#+id/view_div"
android:background="#color/grey"
Doing like above solves the issue.
[This is my screen contains the issue][1]][1]
https://i.stack.imgur.com/CBY80.jpg

Android animating recyclerview

I created a recyclerview with a list of 'events'.This works fine for a list of events that is below 5. but as soon as i get 6 or more events in the list the last event will not expand when clicked, instead it dissapears. the closing animation also stops working with more than 6 events in the list.
how it should behave:
User taps event > view expands to full screen
User taps an expanded event > view collapses back to it's original size
User taps an event while another event is expanded > expanded event is set to original height en tapped event expands to fullscreen
current behavior:
User taps event > all views expand correctly except for the last item in the list
User taps expanded event > view collapses but does not animate
User taps an event while another event is expanded > expanded event collapses and tapped event expands correctly
User taps the last event in the list > the event dissapears (probably decreased it's size to below 0)
I know it probably has something to do with the way the recyclerview reuses its views when they are out of the screen. To fix this i check the position of the tapped event by the eventId instead of the position in the list, but this still leaves the issues that i talked about above.
public class EventRecyclerAdapter extends RecyclerView.Adapter<EventRecyclerAdapter.ViewHolder> {
private Context c;
private List<Event> items = new ArrayList<>();
private RelativeLayout container;
private int screenheight;
private EventListFragment eventListFragment;
private int expandedPosition = -1;
private static final String TAG = "EventRecyclerAdapter";
public interface ItemClickedListener {
void itemClicked(int position);
}
private ItemClickedListener itemClickedListener;
public EventRecyclerAdapter(List<Event> itemlist, Context c, EventListFragment eventListFragment, ItemClickedListener listener) {
this.items = itemlist;
this.c = c;
this.eventListFragment = eventListFragment;
this.itemClickedListener = listener;
}
#Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
// create a new view
View itemLayoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, null);
WindowManager wm = (WindowManager) c.getSystemService(Context.WINDOW_SERVICE);
Display display = wm.getDefaultDisplay();
Point size = new Point();
display.getSize(size);
screenheight = size.y;
// Get the screen height from the device
Resources r = c.getResources();
float px = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 80, r.getDisplayMetrics());
screenheight -= px;
ViewHolder viewHolder = new ViewHolder(itemLayoutView);
return viewHolder;
}
// Replace the contents of a view (invoked by the layout manager)
#Override
public void onBindViewHolder(ViewHolder viewHolder, int position) {
Event event = items.get(position);
// - get data from your itemsData at this position
// - replace the contents of the view with that itemsData
viewHolder.tvName.setText(event.getName());
viewHolder.tvLocation.setText(event.getLocation().getName());
viewHolder.tvDate.setText(Helper.dateDoubleToString(event.getStartDate()));
viewHolder.tvTicketCount.setText(String.valueOf(event.getNumberOfTickets()));
viewHolder.background.setBackgroundColor(Color.GRAY);
viewHolder.eventId = event.getId();
// Load the background image
if (event.getEventImageId() != null) {
Picasso.with(c).load(Helper.imageUrlString(event.getEventImageId())).into(viewHolder.background);
ColorMatrix matrix = new ColorMatrix();
matrix.setSaturation(0);
ColorMatrixColorFilter filter = new ColorMatrixColorFilter(matrix);
viewHolder.background.setColorFilter(filter);
}
// Check if the view needs to be expanded, collapsed or just drawn normally.
if (expandedPosition == event.getId()) {
if (event.expanded) {
collapseView(viewHolder, event);
} else if (!event.expanded) {
expandView(viewHolder, position, event);
}
} else {
setContainerHeight(viewHolder, event);
}
}
private void expandView(final EventRecyclerAdapter.ViewHolder viewHolder, final int pos, Event event) {
ResizeAnimation resizeAnimation = new ResizeAnimation(
viewHolder.container,
viewHolder.container.getHeight(),
screenheight
);
resizeAnimation.setDuration(Constants.ANIMATION_SPEED);
resizeAnimation.setAnimationListener(new Animation.AnimationListener() {
#Override
public void onAnimationStart(Animation animation) {
}
#Override
public void onAnimationEnd(Animation animation) {
viewHolder.infoContainer.setVisibility(View.VISIBLE);
viewHolder.closeIcon.setVisibility(View.VISIBLE);
itemClickedListener.itemClicked(pos);
}
#Override
public void onAnimationRepeat(Animation animation) {
}
});
viewHolder.itemView.startAnimation(resizeAnimation);
viewHolder.expanded = true;
event.expanded = true;
}
private void collapseView(final EventRecyclerAdapter.ViewHolder viewHolder, Event event) {
ResizeAnimation resizeAnimation = new ResizeAnimation(
viewHolder.container,
viewHolder.container.getHeight(),
getContainerCollapsedHeight()
);
resizeAnimation.setDuration(Constants.ANIMATION_SPEED);
viewHolder.infoContainer.setVisibility(View.INVISIBLE);
viewHolder.closeIcon.setVisibility(View.INVISIBLE);
viewHolder.itemView.startAnimation(resizeAnimation);
viewHolder.expanded = false;
event.expanded = false;
}
private void setContainerHeight(EventRecyclerAdapter.ViewHolder viewHolder, Event event) {
viewHolder.container.setLayoutParams(new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, getContainerCollapsedHeight()));
viewHolder.infoContainer.setVisibility(View.INVISIBLE);
viewHolder.closeIcon.setVisibility(View.INVISIBLE);
event.expanded = false;
viewHolder.expanded = false;
}
private int getContainerCollapsedHeight() {
int containerHeight;
// Define the item containers height
if (items.size() <= 3) {
containerHeight = screenheight / items.size();
} else {
containerHeight = screenheight / 3;
}
return containerHeight;
}
/**
* Clear all current data and swap add the new data list.
* The expanded position also gets reset
* #param events
*/
public void swap(List<Event> events) {
this.items.clear();
this.items.addAll(events);
this.expandedPosition = -1;
Log.v(TAG,"SWAP SIZE : " + items.size());
notifyDataSetChanged();
}
// inner class to hold a reference to each item of RecyclerView
class ViewHolder extends RecyclerView.ViewHolder {
public TextView tvLocation, tvDate, tvTicketCount;
public TextView tvName;
public ImageView background;
public View container;
public View infoContainer;
public TextView closeIcon;
public int eventId;
public boolean expanded = false;
public ViewHolder(final View itemLayoutView) {
super(itemLayoutView);
tvName = (TextView) itemLayoutView.findViewById(R.id.tvName);
tvLocation = (TextView) itemLayoutView.findViewById(R.id.tvLocation);
tvDate = (TextView) itemLayoutView.findViewById(R.id.tvDate);
background = (ImageView) itemLayoutView.findViewById(R.id.background);
tvTicketCount = (TextView) itemLayoutView.findViewById(R.id.ticket_count);
container = itemLayoutView.findViewById(R.id.list_item_container);
infoContainer = itemLayoutView.findViewById(R.id.info_container);
closeIcon = (TextView) itemLayoutView.findViewById(R.id.close_icon);
infoContainer.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Activity mainActivity = (Activity) c;
FragmentManager fm = mainActivity.getFragmentManager();
//add
FragmentTransaction ft = fm.beginTransaction();
ft.setCustomAnimations(R.animator.slide_to_top, R.animator.slide_from_bottom);
ft.addToBackStack(ft.toString());
ft.add(R.id.content_frame, EventFragment.newInstance(items.get(getAdapterPosition())), Constants.EVENT_FRAGMENT_TAG);
//commit change
ft.commit();
}
});
container.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
expandedPosition = eventId;
notifyDataSetChanged();
}
});
}
}
// Return the size of your itemsData (invoked by the layout manager)
#Override
public int getItemCount() {
return items.size();
}
}
i think it's somehow running the collapseView method when i tap the last item in the list, causing its height to become below 0. But i'm unable to figure out why this is happening.
I hope someone is able to spot what's wrong here.

you can try this in OnClilck of recycleview Item
#Override
public void onClick(View view)
{
LayoutParams params = view.getLayoutParams();
if (!large)
{
params.height = 2 * view.getHeight();
} else {
params.height = view.getHeight()/2;
}
large = !large;
view.setLayoutParams(params);
}

Auto scroll recyclerview slider

I am new to Android development. I am trying to create an auto scroll recyclerview slider which also supports user events such as next and previous buttons and manual scrolling.
Something like this:
I have implemented the recyclerview and buttons events handling but I don't know how to implementing auto scroll, it is only scrolling from position 0 to the end and how to stop the auto scroll if the user swiped the slider manually or clicked on the buttons.
MainActivity.java
public class MainActivity extends AppCompatActivity {
RecyclerView mRecyclerView;
LinearLayoutManager layoutManager;
HorizontalSliderAdapter recyclerAdapter;
Button btnPrev;
Button btnNext;
Runnable runnable;
Handler handler;
public static final String LOGTAG = "slider";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mRecyclerView = (RecyclerView) findViewById(R.id.horizontal_slider_recyclerview);
setUpRecyclerView();
autoScroll();
}
public void setUpRecyclerView() {
final List<HorizontalSliderModel> RowItems = HorizontalSliderModel.getData();
layoutManager = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
mRecyclerView.setLayoutManager(layoutManager);
mRecyclerView.setHasFixedSize(true);
recyclerAdapter = new HorizontalSliderAdapter(this, RowItems);
mRecyclerView.setAdapter(recyclerAdapter);
btnPrev = (Button) findViewById(R.id.bPrev);
btnNext = (Button) findViewById(R.id.bNext);
btnPrev.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mRecyclerView.getLayoutManager().scrollToPosition(layoutManager.findFirstVisibleItemPosition() - 1);
}
});
btnNext.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mRecyclerView.getLayoutManager().scrollToPosition(layoutManager.findLastVisibleItemPosition() + 1);
}
});
mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
switch (newState) {
case RecyclerView.SCROLL_STATE_IDLE:
float targetBottomPosition1 = mRecyclerView.getX();
float targetBottomPosition2 = mRecyclerView.getX() + mRecyclerView.getWidth();
Log.i(LOGTAG, "targetBottomPosition1 = " + targetBottomPosition1);
Log.i(LOGTAG, "targetBottomPosition2 = " + targetBottomPosition2);
View v1 = mRecyclerView.findChildViewUnder(targetBottomPosition1, 0);
View v2 = mRecyclerView.findChildViewUnder(targetBottomPosition2, 0);
float x1 = targetBottomPosition1;
if (v1 != null) {
x1 = v1.getX();
}
float x2 = targetBottomPosition2;
if (v2 != null) {
x2 = v2.getX();
}
Log.i(LOGTAG, "x1 = " + x1);
Log.i(LOGTAG, "x2 = " + x2);
float dx1 = Math.abs(mRecyclerView.getX() - x1);
float dx2 = Math.abs(mRecyclerView.getX() + mRecyclerView.getWidth() - x2);
Log.i(LOGTAG, "dx1 = " + dx1);
Log.i(LOGTAG, "dx2 = " + dx2);
float visiblePortionOfItem1 = 0;
float visiblePortionOfItem2 = 0;
if (x1 < 0 && v1 != null) {
visiblePortionOfItem1 = v1.getWidth() - dx1;
}
if (v2 != null) {
visiblePortionOfItem2 = v2.getWidth() - dx2;
}
Log.i(LOGTAG, "visiblePortionOfItem1 = " + visiblePortionOfItem1);
Log.i(LOGTAG, "visiblePortionOfItem2 = " + visiblePortionOfItem2);
int position = 0;
if (visiblePortionOfItem1 >= visiblePortionOfItem2) {
position = mRecyclerView.getChildAdapterPosition(mRecyclerView.findChildViewUnder(targetBottomPosition1, 0));
} else {
position = mRecyclerView.getChildAdapterPosition(mRecyclerView.findChildViewUnder(targetBottomPosition2, 0));
}
mRecyclerView.scrollToPosition(position);
break;
case RecyclerView.SCROLL_STATE_DRAGGING:
break;
case RecyclerView.SCROLL_STATE_SETTLING:
break;
}
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
}
});
}
public void autoScroll() {
final int speedScroll = 2000;
handler = new Handler();
runnable = new Runnable() {
int count = -1;
#Override
public void run() {
if (count < mRecyclerView.getAdapter().getItemCount()) {
mRecyclerView.smoothScrollToPosition(++count);
handler.postDelayed(this, speedScroll);
}
if (count == mRecyclerView.getAdapter().getItemCount()) {
mRecyclerView.setLayoutManager(new LinearLayoutManagerWithSmoothScroller(MainActivity.this));
mRecyclerView.smoothScrollToPosition(--count);
handler.postDelayed(this, speedScroll);
}
}
};
handler.post(runnable);
}
}

About the auto-scroll, I just started a new master/detail template in Android Studio.
Can you try to use this class as your recyclerView's layout manager ?
public class ScrollingLinearLayoutManager extends LinearLayoutManager {
private final int duration;
public ScrollingLinearLayoutManager(Context context, int orientation, boolean reverseLayout, int duration) {
super(context, orientation, reverseLayout);
this.duration = duration;
}
#Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state,
int position) {
View firstVisibleChild = recyclerView.getChildAt(0);
int itemHeight = firstVisibleChild.getHeight();
int currentPosition = recyclerView.getChildLayoutPosition(firstVisibleChild);
int distanceInPixels = Math.abs((currentPosition - position) * itemHeight);
if (distanceInPixels == 0) {
distanceInPixels = (int) Math.abs(firstVisibleChild.getY());
}
SmoothScroller smoothScroller = new SmoothScroller(recyclerView.getContext(), distanceInPixels, duration);
smoothScroller.setTargetPosition(position);
startSmoothScroll(smoothScroller);
}
private class SmoothScroller extends LinearSmoothScroller {
private final float distanceInPixels;
private final float duration;
public SmoothScroller(Context context, int distanceInPixels, int duration) {
super(context);
this.distanceInPixels = distanceInPixels;
this.duration = duration;
}
#Override
public PointF computeScrollVectorForPosition(int targetPosition) {
return ScrollingLinearLayoutManager.this
.computeScrollVectorForPosition(targetPosition);
}
#Override
protected int calculateTimeForScrolling(int dx) {
float proportion = (float) dx / distanceInPixels;
return (int) (duration * proportion);
}
}
}
And set it like this
recyclerView.setAdapter(new SimpleItemRecyclerViewAdapter(DummyContent.ITEMS));
recyclerView.setLayoutManager(new ScrollingLinearLayoutManager(this, LinearLayoutManager.VERTICAL, false, 5000));
And trigger it this way
recyclerView.smoothScrollToPosition(recyclerView.getAdapter().getItemCount());

PagerSnapHelper solved my problem.
binding.recyclerViewHomeAnnouncement.apply {
layoutManager = LinearLayoutManager(activity, LinearLayoutManager.HORIZONTAL, false)
binding.recyclerViewHomeAnnouncement.layoutManager = layoutManager
setHasFixedSize(true)
itemAnimator = DefaultItemAnimator()
adapter = homeAnnouncementAdapter
}
val snapHelper: SnapHelper = PagerSnapHelper()
snapHelper.attachToRecyclerView(binding.recyclerViewHomeAnnouncement)

Get center visible item of RecycleView when scrolling

This is what I want:
As image above, I want to draw a center line on RecycleView, then get the center item when scrolling (as well as move left or right)
Here is my try to draw a horizontal RecycleView:
HorizontalAdapter adapter = new HorizontalAdapter(data);
LinearLayoutManager layoutManager
= new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
recycleView.setLayoutManager(layoutManager);
recycleView.setAdapter(adapter);
Is there any way to know which item is moved to the center of RecycleView? And how can I scroll RecycleView to left or right just one position?
Update: I tried to use a scroll listener to get the middle position, but it doesn't work as an aspect.
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
int firstPos = layoutManager.findFirstVisibleItemPosition();
int lastPos = layoutManager.findLastVisibleItemPosition();
int middle = Math.abs(lastPos - firstPos) / 2 + firstPos;
int selectedPos = -1;
for (int i = 0; i < adapter.getItemCount(); i++) {
if (i == middle) {
adapter.getItem(i).setSelected(true);
selectedPos = i;
} else {
adapter.getItem(i).setSelected(false);
}
}
adapter.notifyDataSetChanged();
}
And get the result:
I only want to change the selected item (make text to white color) when it is on the blue Rect

I made something just like this. I can do exactly what you need.
First of all, this is how is my alogrithm work
This is my recyclerView Adapter
public class DateAdapter extends RecyclerView.Adapter<DateAdapter.DateViewHolder> {
private ArrayList<LabelerDate> dateDataList;
private static final int VIEW_TYPE_PADDING = 1;
private static final int VIEW_TYPE_ITEM = 2;
private int paddingWidthDate = 0;
private int selectedItem = -1;
public DateAdapter(ArrayList<LabelerDate> dateData, int paddingWidthDate) {
this.dateDataList = dateData;
this.paddingWidthDate = paddingWidthDate;
}
#Override
public DateViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == VIEW_TYPE_ITEM) {
final View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_date,
parent, false);
return new DateViewHolder(view);
} else {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_padding,
parent, false);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) view.getLayoutParams();
layoutParams.width = paddingWidthDate;
view.setLayoutParams(layoutParams);
return new DateViewHolder(view);
}
}
#Override
public void onBindViewHolder(DateViewHolder holder, int position) {
LabelerDate labelerDate = dateDataList.get(position);
if (getItemViewType(position) == VIEW_TYPE_ITEM) {
if(labelerDate.dateType.equals(BirthDayActivity.DateType.C31))
holder.tvDate.setText(String.valueOf(labelerDate.valueDate));
holder.tvDate.setVisibility(View.VISIBLE);
holder.imgSmall.setVisibility(View.VISIBLE);
if (position == selectedItem) {
holder.tvDate.setTextColor(Color.parseColor("#094673"));
holder.tvDate.setTextSize(35);
holder.imgSmall.setBackgroundResource(R.color.textviewbold);
} else {
holder.tvDate.setTextColor(Color.GRAY);
holder.tvDate.setTextSize(35);
holder.imgSmall.setBackgroundResource(R.color.gray);
}
}
}
public void setSelecteditem(int selecteditem) {
this.selectedItem = selecteditem;
notifyDataSetChanged();
}
#Override
public int getItemCount() {
return dateDataList.size();
}
#Override
public int getItemViewType(int position) {
LabelerDate labelerDate = dateDataList.get(position);
if (labelerDate.dateType.equals(BirthDayActivity.DateType.NONE)) {
return VIEW_TYPE_PADDING;
}
return VIEW_TYPE_ITEM;
}
public class DateViewHolder extends RecyclerView.ViewHolder {
public TextView tvDate;
public ImageView imgSmall;
public DateViewHolder(View itemView) {
super(itemView);
tvDate = (TextView) itemView.findViewById(R.id.tvNumberDate);
imgSmall = (ImageView) itemView.findViewById(R.id.small_marked_dob);
}
}}
This is most important alogrithm:
public void getRecyclerviewDate() {
recyclerViewDate = (RecyclerView) findViewById(R.id.recyclerViewDay);
ViewTreeObserver vtoDate = recyclerViewDate.getViewTreeObserver();
vtoDate.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
#Override
public boolean onPreDraw() {
recyclerViewDate.getViewTreeObserver().removeOnPreDrawListener(this);
finalWidthDate = recyclerViewDate.getMeasuredWidth();
itemWidthDate = getResources().getDimension(R.dimen.item_dob_width);
paddingDate = (finalWidthDate - itemWidthDate) / 2;
firstItemWidthDate = paddingDate ;
allPixelsDate = 0;
final LinearLayoutManager dateLayoutManager = new LinearLayoutManager(getApplicationContext());
dateLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
recyclerViewDate.setLayoutManager(dateLayoutManager);
recyclerViewDate.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
synchronized (this) {
if(newState == RecyclerView.SCROLL_STATE_IDLE){
calculatePositionAndScrollDate(recyclerView);
}
}
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
allPixelsDate += dx;
}
});
if (labelerDates == null)
labelerDates = new ArrayList<>();
labelerDates.addAll(genLabelerDate(currentMonth, currentYear));
dateAdapter = new DateAdapter(labelerDates, (int) firstItemWidthDate);
recyclerViewDate.setAdapter(dateAdapter);
return true;
}
});
}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
private void calculatePositionAndScrollDate(RecyclerView recyclerView) {
int expectedPositionDate = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
if (expectedPositionDate == -1) {
expectedPositionDate = 0;
} else if (expectedPositionDate >= recyclerView.getAdapter().getItemCount() - 2) {
expectedPositionDate--;
}
scrollListToPositionDate(recyclerView, expectedPositionDate);
}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
private void scrollListToPositionDate(RecyclerView recyclerView, int expectedPositionDate) {
float targetScrollPosDate = expectedPositionDate * itemWidthDate + firstItemWidthDate - paddingDate;
float missingPxDate = targetScrollPosDate - allPixelsDate;
if (missingPxDate != 0) {
recyclerView.smoothScrollBy((int) missingPxDate, 0);
}
}
private void setDateValue() {
int expectedPositionDateColor = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
setColorDate = expectedPositionDateColor + 1;
//set color here
dateAdapter.setSelecteditem(setColorDate);
}
#Override
protected void onRestoreInstanceState(#NonNull Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
allPixelsDate = savedInstanceState.getFloat(BUNDLE_LIST_PIXELS_DATE);
allPixelsDateChanged = savedInstanceState.getFloat(BUNDLE_LIST_PIXELS_DATE_CHANGED);
}
#Override
protected void onSaveInstanceState(#NonNull Bundle outState) {
super.onSaveInstanceState(outState);
outState.putFloat(BUNDLE_LIST_PIXELS_DATE, allPixelsDate);
outState.putFloat(BUNDLE_LIST_PIXELS_DATE_CHANGED, allPixelsDateChanged);
}
And this is my result:
Look at this video link, this is my app demo

Sometimes is needed the entire example code block together, because we may miss something. Here is what I have, feel free to correct anything since I may be doing some little mistake somewhere. And Yes, this answer is an extension of #tranhieu answer. Thanks #tranhieu.
MainActivity.java
package com.test;
import android.app.Activity;
import android.graphics.Color;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.TextView;
import java.util.ArrayList;
public class MainActivity extends Activity {
private static final String TAG = MainActivity.class.getSimpleName();
public float firstItemWidthDate;
public float paddingDate;
public float itemWidthDate;
public int allPixelsDate;
public int finalWidthDate;
private DateAdapter dateAdapter;
private ArrayList<LabelerDate> labelerDates = new ArrayList<>();
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getRecyclerviewDate();
}
public void getRecyclerviewDate() {
final RecyclerView recyclerViewDate = (RecyclerView) findViewById(R.id.rv_tasks_date);
if (recyclerViewDate != null) {
recyclerViewDate.postDelayed(new Runnable() {
#Override
public void run() {
setDateValue();
}
}, 300);
recyclerViewDate.postDelayed(new Runnable() {
#Override
public void run() {
recyclerViewDate.smoothScrollToPosition(dateAdapter.getItemCount()-1);
setDateValue();
}
}, 5000);
}
ViewTreeObserver vtoDate = recyclerViewDate.getViewTreeObserver();
vtoDate.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
#Override
public boolean onPreDraw() {
recyclerViewDate.getViewTreeObserver().removeOnPreDrawListener(this);
finalWidthDate = recyclerViewDate.getMeasuredWidth();
itemWidthDate = getResources().getDimension(R.dimen.item_dob_width);
paddingDate = (finalWidthDate - itemWidthDate) / 2;
firstItemWidthDate = paddingDate;
allPixelsDate = 0;
final LinearLayoutManager dateLayoutManager = new LinearLayoutManager(getApplicationContext());
dateLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
recyclerViewDate.setLayoutManager(dateLayoutManager);
recyclerViewDate.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
synchronized (this) {
if (newState == RecyclerView.SCROLL_STATE_IDLE) {
calculatePositionAndScrollDate(recyclerView);
}
}
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
allPixelsDate += dx;
}
});
if (labelerDates == null) {
labelerDates = new ArrayList<>();
}
genLabelerDate();
dateAdapter = new DateAdapter(labelerDates, (int) firstItemWidthDate);
recyclerViewDate.setAdapter(dateAdapter);
dateAdapter.setSelecteditem(dateAdapter.getItemCount() - 1);
return true;
}
});
}
private void genLabelerDate() {
for (int i = 0; i < 32; i++) {
LabelerDate labelerDate = new LabelerDate();
labelerDate.setNumber(Integer.toString(i));
labelerDates.add(labelerDate);
if (i == 0 || i == 31) {
labelerDate.setType(DateAdapter.VIEW_TYPE_PADDING);
} else {
labelerDate.setType(DateAdapter.VIEW_TYPE_ITEM);
}
}
}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
private void calculatePositionAndScrollDate(RecyclerView recyclerView) {
int expectedPositionDate = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
if (expectedPositionDate == -1) {
expectedPositionDate = 0;
} else if (expectedPositionDate >= recyclerView.getAdapter().getItemCount() - 2) {
expectedPositionDate--;
}
scrollListToPositionDate(recyclerView, expectedPositionDate);
}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
private void scrollListToPositionDate(RecyclerView recyclerView, int expectedPositionDate) {
float targetScrollPosDate = expectedPositionDate * itemWidthDate + firstItemWidthDate - paddingDate;
float missingPxDate = targetScrollPosDate - allPixelsDate;
if (missingPxDate != 0) {
recyclerView.smoothScrollBy((int) missingPxDate, 0);
}
setDateValue();
}
//
private void setDateValue() {
int expectedPositionDateColor = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
int setColorDate = expectedPositionDateColor + 1;
// set color here
dateAdapter.setSelecteditem(setColorDate);
}
public class DateAdapter extends RecyclerView.Adapter<DateAdapter.DateViewHolder> {
private ArrayList<LabelerDate> dateDataList;
private static final int VIEW_TYPE_PADDING = 1;
private static final int VIEW_TYPE_ITEM = 2;
private int paddingWidthDate = 0;
private int selectedItem = -1;
public DateAdapter(ArrayList<LabelerDate> dateData, int paddingWidthDate) {
this.dateDataList = dateData;
this.paddingWidthDate = paddingWidthDate;
}
#Override
public DateViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == VIEW_TYPE_ITEM) {
final View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item,
parent, false);
return new DateViewHolder(view);
} else {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item,
parent, false);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) view.getLayoutParams();
layoutParams.width = paddingWidthDate;
view.setLayoutParams(layoutParams);
return new DateViewHolder(view);
}
}
#Override
public void onBindViewHolder(DateViewHolder holder, int position) {
LabelerDate labelerDate = dateDataList.get(position);
if (getItemViewType(position) == VIEW_TYPE_ITEM) {
holder.tvDate.setText(labelerDate.getNumber());
holder.tvDate.setVisibility(View.VISIBLE);
Log.d(TAG, "default " + position + ", selected " + selectedItem);
if (position == selectedItem) {
Log.d(TAG, "center" + position);
holder.tvDate.setTextColor(Color.parseColor("#76FF03"));
holder.tvDate.setTextSize(35);
} else {
holder.tvDate.setTextColor(Color.WHITE);
holder.tvDate.setTextSize(18);
}
} else {
holder.tvDate.setVisibility(View.INVISIBLE);
}
}
public void setSelecteditem(int selecteditem) {
this.selectedItem = selecteditem;
notifyDataSetChanged();
}
#Override
public int getItemCount() {
return dateDataList.size();
}
#Override
public int getItemViewType(int position) {
LabelerDate labelerDate = dateDataList.get(position);
if (labelerDate.getType() == VIEW_TYPE_PADDING) {
return VIEW_TYPE_PADDING;
} else {
return VIEW_TYPE_ITEM;
}
}
public class DateViewHolder extends RecyclerView.ViewHolder {
public TextView tvDate;
public DateViewHolder(View itemView) {
super(itemView);
tvDate = (TextView) itemView.findViewById(R.id.txt_date);
}
}
}
private class LabelerDate {
private int type;
private String number;
public String getNumber() {
return number;
}
public void setNumber(String number) {
this.number = number;
}
public int getType() {
return type;
}
public void setType(int type) {
this.type = type;
}
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<FrameLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.v7.widget.RecyclerView
android:id="#+id/rv_tasks_date"
android:layout_width="match_parent"
android:layout_height="48dp" />
<ImageView
android:layout_width="48dp"
android:layout_height="48dp"
android:layout_gravity="center"
android:layout_marginTop="48dp"
android:src="#android:drawable/ic_dialog_info" />
</FrameLayout>
</LinearLayout>
item.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="wrap_content"
android:layout_height="match_parent">
<TextView
android:id="#+id/txt_date"
android:layout_width="#dimen/item_dob_width"
android:layout_height="48dp"
android:text="32"
android:textColor="#android:color/white"
android:background="#android:color/darker_gray"
android:textSize="28sp"
android:gravity="center"/>
</LinearLayout>
dimens.xml
<resources>
<dimen name="item_dob_width">100dp</dimen>
</resources>

Oh boy. I've been searching for this answer for almost a week and then found out the solution. Custom LayoutManagers? No. ItemDecorator? Nope.
Here's the easiest way to do it:
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:paddingStart="150dp"
android:paddingEnd="150dp"
android:clipToPadding="false" />
The critical part is:
android:paddingStart="150dp"
android:paddingEnd="150dp"
android:clipToPadding="false"
And then just assign SnapHelper to your RecylcerView:
val snapHelper = LinearSnapHelper()
snapHelper.attachToRecyclerView(recyclerView)
This is it. The easiest and most perfect solution to the problem

I'm used the SnapHelper right here:
// init snaphelper
SnapHelper snapHelper = new LinearSnapHelper();
snapHelper.attachToRecyclerView(recyclerView)
// init layout manager
LinearLayoutManager layoutManager = new LinearLayoutManager(mainActivity);
layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
recyclerView.setLayoutManager(layoutManager);
// init adapter
adatper.setSnapHelper(snapHelper);
adatper.setLayoutManager(layoutManager);
adatper.initAdapter(new Float((DisplayHelper.getDisplayWidth(mainActivity) / 2) - (fooViewWidth / 2)).intValue());
recyclerView.setAdapter(adatper);
As said by TranHieu the solution of inserting 2 item for padding (at start and at end positions) is good.
I don't like the use of ViewTreeObserver because of poor readability of code. With this technique then you must also manage redrawing of the items if they are recycled.
If you are using customview classes you can set its width directly into these classes.
For example this is my padding class
/**
* Created by firegloves on 25/09/15.
*/
#EViewGroup(R.layout.view_padding)
public class PaddingView extends FooView {
Context mCtx;
public PaddingView(Context context) {
super(context);
mCtx = context;
}
public void setWidth(int width) {
setLayoutParams(new LayoutParams(width, ViewGroup.LayoutParams.WRAP_CONTENT));
}
}
In my adapter I store the desired padding item width, that is equal to (displayWidth / 2) - (realItemWidth / 2)
This is my adapter, don't look at methods not matching RecyclerView.Adapter, pay attention to the initAdapter method and to the onCreateItemView method
#EBean
public class FooAdapterRecycler extends RecyclerViewAdapterBase<Foo, FooView> {
private final int TYPE_PADDING_VIEW = 0;
private final int TYPE_REAL_VIEW = 1;
#RootContext
Context ctx;
#Bean(Finder.class)
IFinder finder;
SnapHelper snapHelper;
RecyclerView.LayoutManager layoutManager;
private int paddingWidth = 0;
/**
* preleva i dati dal finder
*/
public void initAdapter(int paddingWidth) {
/*******************************
* THIS CODE IS THE IMPORTANT ONE
******************************/
this.paddingWidth = paddingWidth;
// add 1 item for initial space
mItems = new ArrayList<>();
Foo foo = new Foo();
mItems.add(foo);
// get real items from finder
mItems.addAll(finder.findAll());
// add 1 item for final space
mItems = new ArrayList<>();
Foo foo2 = new Foo();
mItems.add(foo2);
}
#Override
public int getItemViewType(int position) {
if (position == 0 || position == getItemCount()-1) {
return TYPE_PADDING_VIEW;
} else {
return TYPE_REAL_VIEW;
}
}
#Override
protected FooView onCreateItemView(ViewGroup parent, int viewType) {
/*******************************
* THIS CODE IS THE IMPORTANT ONE
******************************/
if (viewType == TYPE_PADDING_VIEW) {
PaddingView view = PaddingView_.build(ctx);
view.setWidth(paddingWidth);
return view;
} else {
return FooView_.build(ctx);
}
}
public void setSnapHelper(SnapHelper snapHelper) {
this.snapHelper = snapHelper;
}
public void setLayoutManager(RecyclerView.LayoutManager layoutManager) {
this.layoutManager = layoutManager;
}
}
I'm using AndroidAnnotations library but it's not required
Hope that helps

USING SNAPHELPER - A SMOOTHER SOLUTION
Here it is another solution using SnapHelper. Starting from the answer of #TranHieu here:
https://stackoverflow.com/a/34647005/3944251
and the compressed by #sector11 here:
https://stackoverflow.com/a/38411582/3944251
I wrote the following code which is also based in both answers above, but it's simpler and offers a smoother solution using SnapHelper presented in android support library 24.2.0.
Here you have the MainActivity class. The rest is the same with #sector11's answer.
import android.graphics.Color;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.LinearSnapHelper;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.TextView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
private static final String TAG = MainActivity.class.getSimpleName();
public float firstItemWidthDate;
public float itemWidthDate;
public int allPixelsDate;
public int finalWidthDate;
private DateAdapter dateAdapter;
private ArrayList<LabelerDate> labelerDates;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
labelerDates = new ArrayList<>();
getRecyclerviewDate();
}
public void getRecyclerviewDate() {
final RecyclerView recyclerViewDate = (RecyclerView) findViewById(R.id.rv_tasks_date);
recyclerViewDate.postDelayed(new Runnable() {
#Override
public void run() {
//recyclerViewDate.smoothScrollToPosition(dateAdapter.getItemCount()-1);
setDateValue();
}
}, 300);
ViewTreeObserver vtoDate = recyclerViewDate.getViewTreeObserver();
vtoDate.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
#Override
public boolean onPreDraw() {
recyclerViewDate.getViewTreeObserver().removeOnPreDrawListener(this);
finalWidthDate = recyclerViewDate.getMeasuredWidth();
itemWidthDate = getResources().getDimension(R.dimen.item_dob_width);
firstItemWidthDate = (finalWidthDate - itemWidthDate) / 2;
allPixelsDate = 0;
final LinearLayoutManager dateLayoutManager = new LinearLayoutManager(getApplicationContext());
dateLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
recyclerViewDate.setLayoutManager(dateLayoutManager);
/* Create a LinearSnapHelper and attach the recyclerView to it. */
final LinearSnapHelper snapHelper = new LinearSnapHelper();
snapHelper.attachToRecyclerView(recyclerViewDate);
recyclerViewDate.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
allPixelsDate += dx;
recyclerView.post(new Runnable() {
public void run() {
setDateValue();
}
});
}
});
genLabelerDate();
dateAdapter = new DateAdapter(labelerDates, (int) firstItemWidthDate);
recyclerViewDate.setAdapter(dateAdapter);
dateAdapter.setSelecteditem(dateAdapter.getItemCount() - 1);
return true;
}
});
}
private void genLabelerDate() {
for (int i = 0; i < 32; i++) {
LabelerDate labelerDate = new LabelerDate();
labelerDate.setNumber(Integer.toString(i));
labelerDates.add(labelerDate);
if (i == 0 || i == 31) {
labelerDate.setType(DateAdapter.VIEW_TYPE_PADDING);
} else {
labelerDate.setType(DateAdapter.VIEW_TYPE_ITEM);
}
}
}
//
private void setDateValue() {
int expectedPositionDateColor = Math.round(allPixelsDate / itemWidthDate);
int setColorDate = expectedPositionDateColor + 1;
// set color here
dateAdapter.setSelecteditem(setColorDate);
}
public class DateAdapter extends RecyclerView.Adapter<DateAdapter.DateViewHolder> {
private ArrayList<LabelerDate> dateDataList;
private static final int VIEW_TYPE_PADDING = 1;
private static final int VIEW_TYPE_ITEM = 2;
private int paddingWidthDate = 0;
private int selectedItem = -1;
public DateAdapter(ArrayList<LabelerDate> dateData, int paddingWidthDate) {
this.dateDataList = dateData;
this.paddingWidthDate = paddingWidthDate;
}
#Override
public DateAdapter.DateViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false);
if (viewType == VIEW_TYPE_PADDING) {
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) view.getLayoutParams();
layoutParams.width = paddingWidthDate;
view.setLayoutParams(layoutParams);
}
return new DateViewHolder(view);
}
#Override
public void onBindViewHolder(DateAdapter.DateViewHolder holder, int position) {
LabelerDate labelerDate = dateDataList.get(position);
if (getItemViewType(position) == VIEW_TYPE_ITEM) {
holder.tvDate.setText(labelerDate.getNumber());
holder.tvDate.setVisibility(View.VISIBLE);
Log.d(TAG, "default " + position + ", selected " + selectedItem);
if (position == selectedItem) {
Log.d(TAG, "center" + position);
holder.tvDate.setTextColor(Color.parseColor("#76FF03"));
holder.tvDate.setTextSize(35);
} else {
holder.tvDate.setTextColor(Color.WHITE);
holder.tvDate.setTextSize(18);
}
} else {
holder.tvDate.setVisibility(View.INVISIBLE);
}
}
public void setSelecteditem(int selecteditem) {
this.selectedItem = selecteditem;
notifyDataSetChanged();
}
#Override
public int getItemCount() {
return dateDataList.size();
}
#Override
public int getItemViewType(int position) {
LabelerDate labelerDate = dateDataList.get(position);
if (labelerDate.getType() == VIEW_TYPE_PADDING) {
return VIEW_TYPE_PADDING;
} else {
return VIEW_TYPE_ITEM;
}
}
public class DateViewHolder extends RecyclerView.ViewHolder {
public TextView tvDate;
public DateViewHolder(View itemView) {
super(itemView);
tvDate = (TextView) itemView.findViewById(R.id.txt_date);
}
}
}
private class LabelerDate {
private int type;
private String number;
public String getNumber() {
return number;
}
public void setNumber(String number) {
this.number = number;
}
public int getType() {
return type;
}
public void setType(int type) {
this.type = type;
}
}
}

You can use a LinearSnapHelper
Attach to your recyclerView like
val snapHelper = LinearSnapHelper()
snapHelper.attachToRecyclerView(this)
Then, to get the center view, use
snapHelper.findSnapView(horizontalScrollView.layoutManager)?

As mentioned in the other answer, there is no direct way to do this.
This is probably how you can achieve what you described in the question.
Know the number of items visible on the screen.
Select the middle item programmatically every time the view is scrolled.
Keep a partially transparent image as an overlay on the middle item on the recyclerview. (You'll need to compute the coordinates based on the width of the recycler view or width of the screen and the width of the overlay image you choose to put.
Refresh the selected value in a text view below the recycler view every time there is a scroll.
The image overlays have to be placed in a way they appear connected and as one single control.

For this feature use EcoGallery library:
https://github.com/falnatsheh/EcoGallery

At first, I needed something similar, not this. But I was able to adapt #TranHieu solution to my needs, so I voted up his solution.
I wanted to create full-screen horizontal recyclerview that after user sroll updates scrollPosition to mostVisibleItem.
setup:
private void setUpScrolling() {
mRecyclerVIew.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
#Override
public boolean onPreDraw() {
mRecyclerVIew.getViewTreeObserver().removeOnPreDrawListener(this);
CustomScrollListener listener = (CustomScrollListener) mScrollListener;
listener.width = mRecyclerVIew.getMeasuredWidth();
listener.dx = 0;
return true;
}
});
}
listener:
private class CustomScrollListener extends OnScrollListener {
private int mLastDx = 0;
int width = 0;
int dx = 0;
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
if (newState == RecyclerView.SCROLL_STATE_IDLE) {
if (mLastDx != dx) {
scrollToMostVisibleItem();
} else {
dx = 0;
mLastDx = 0;
}
}
super.onScrollStateChanged(recyclerView, newState);
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
this.dx += dx;
}
private void scrollToMostVisibleItem() {
int direction = (dx > 0) ? 1 : -1;
dx = Math.abs(dx);
int shiftCount = Math.round(dx / width);
int pixelShift = dx % width;
if (pixelShift > width / 2) {
shiftCount++;
}
float targetScrollPixels = shiftCount * width;
float finalScrollPixels = (targetScrollPixels - dx) * direction;
if (finalScrollPixels != 0) {
mRecyclerVIew.smoothScrollBy((int) finalScrollPixels, 0);
mLastDx = (int) finalScrollPixels;
dx = 0;
}
}
}

I used another approach in my case.
you can find the deatils here: RecyclerView - How highlight central visible item during scroll1
In my opinion, my solution is more easy than the others.

If someone is looking for a more generic implementation, here is my code based on the answers of this thread:
Add the CenterLinearSnapHelper
public class CenterLinearSnapHelper extends LinearSnapHelper {
//Constants
public static final String TAG = CenterLinearSnapHelper.class.getSimpleName();
//Attributes
private Context context;
private float itemWidth;
private OnPaddingComputationListener listener;
//Constructors
/**
* A linear snap helper which helps centering the items in a recyclerview.
*
* #param itemWidth The (fixed) width of a child view in pixels.
*/
public CenterLinearSnapHelper(float itemWidth) {
this.itemWidth = itemWidth;
}
public void attachToRecyclerView(#Nullable RecyclerView recyclerView,
#NonNull OnPaddingComputationListener listener) throws IllegalStateException {
this.listener = listener;
//Calculates the padding for the first and end item
calculatePadding(recyclerView);
//Create a LinearSnapHelper and attach the recyclerView to it.
attachToRecyclerView(recyclerView);
}
public float getItemWidth() {
return itemWidth;
}
private void calculatePadding(RecyclerView recyclerView) {
if (recyclerView == null)
return;
ViewTreeObserver observer = recyclerView.getViewTreeObserver();
observer.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
#Override
public boolean onPreDraw() {
recyclerView.getViewTreeObserver().removeOnPreDrawListener(this);
int finalWidth = recyclerView.getMeasuredWidth();
float padding = (finalWidth - itemWidth) / 2;
listener.onPadding(padding, finalWidth);
return true;
}
});
}
public interface OnPaddingComputationListener {
void onPadding(float padding, int finalWidth);
}
}
In your Activity/Fragment where you create your RecyclerView:
float itemWidth = getResources().getDimension(R.dimen.favorite_room_width);
CenterLinearSnapHelper snapHelper = new CenterLinearSnapHelper(itemWidth);
snapHelper.attachToRecyclerView(binding.listFavorites, (padding, finalWidth) -> {
//Set the adapter
roomAdapter = new RoomAdapter(requireContext(), rooms);
roomAdapter.addPaddingItems((int) padding);
roomAdapter.setOnToggleClickListener(FavoritesFragment.this);
binding.listFavorites.setAdapter(roomAdapter);
});
In your adapter:
public void addPaddingItems(int padding) {
if (padding < 0)
throw new IllegalStateException("Padding cannot be smaller than 0");
this.padding = padding;
//Add 2 new items as the first and last
//NOTE: If you update your existing dataset (e.g add new items), you should redo the calculation!
rooms.add(0, new Room("First"));
rooms.add(rooms.size(), new Room("Last"));
}
#Override
public int getItemViewType(int position) {
if (padding >= 0 && (position == 0 || position == rooms.size() - 1)) {
return VIEW_TYPE_PADDING;
}
return VIEW_TYPE_ITEM;
}
#NonNull
#Override
public RoomViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
ViewFavoriteRoomBinding binding = DataBindingUtil.inflate(inflater, R.layout.view_favorite_room, parent, false);
if (viewType == VIEW_TYPE_PADDING) {
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) binding.getRoot().getLayoutParams();
layoutParams.width = padding;
binding.getRoot().setLayoutParams(layoutParams);
}
RoomViewHolder viewHolder = new RoomViewHolder(context, binding, onToggleClickListener);
viewHolder.getRecyclerView().setRecycledViewPool(viewPool);
return viewHolder;
}

Is there a way to create preview slider in android

I'm trying to create interface like
.
Central element is ViewPager with full-size image, top element is RecyclerView with preview images. But I couldn't find the way to magnet elements to center. Is there way to override behavior of RecyclerView?

I found the solution exactly what you need. I created a small example on github.com: AndroidPreviewSlider
The thing is that top view is ViewPager and center view is ViewPager too.
Detailed code is below:
Adapter for top preview
public class PhotoPreviewAdapter extends FragmentPagerAdapter {
private static final int DEFAULT_SIDE_PREVIEW_COUNT = 3;
private final int sidePreviewCount;
private final List<PhotoInfo> photoInfos;
public PhotoPreviewAdapter(FragmentManager fm, List<PhotoInfo> photoInfos) {
this(fm, DEFAULT_SIDE_PREVIEW_COUNT, photoInfos);
}
public PhotoPreviewAdapter(FragmentManager fm, int sidePreviewCount, List<PhotoInfo> photoInfos) {
super(fm);
this.sidePreviewCount = sidePreviewCount;
this.photoInfos = photoInfos;
}
public int getSidePreviewCount() {
return sidePreviewCount;
}
#Override
public Fragment getItem(int position) {
if (isDummy(position)) {
return DummyPreviewFragment.newInstance();
} else {
return PhotoPreviewFragment.newInstance(photoInfos.get(getRealPosition(position)));
}
}
private boolean isDummy(int position) {
return position < sidePreviewCount || position > photoInfos.size() - 1 + sidePreviewCount;
}
private int getRealPosition(int position) {
return position - sidePreviewCount;
}
#Override
public int getCount() {
return photoInfos.size() + (sidePreviewCount * 2);
}
#Override
public float getPageWidth(int position) {
return 1.0f / getElementsPerPage();
}
private int getElementsPerPage() {
return (sidePreviewCount * 2) + 1;
}
}
Adapter for central view is simple
public class PhotoViewAdapter extends FragmentPagerAdapter {
private final List<PhotoInfo> photoInfos;
public PhotoViewAdapter(FragmentManager fm, List<PhotoInfo> photoInfos) {
super(fm);
this.photoInfos = photoInfos;
}
#Override
public Fragment getItem(int position) {
return PhotoViewFragment.newInstance(photoInfos.get(position));
}
#Override
public int getCount() {
return photoInfos.size();
}
}
And one of the main is sync listener
public class OnSyncPageChangeListener implements ViewPager.OnPageChangeListener {
private int scrollState = ViewPager.SCROLL_STATE_IDLE;
private final ViewPager syncToViewPager;
private final ViewPager syncWithViewPager;
public OnSyncPageChangeListener(ViewPager syncToViewPager, ViewPager syncWithViewPager) {
this.syncToViewPager = syncToViewPager;
this.syncWithViewPager = syncWithViewPager;
}
#Override
public void onPageScrolled(final int position, final float positionOffset, final int positionOffsetPixels) {
if (scrollState != ViewPager.SCROLL_STATE_IDLE) {
final float ratio = calculateRatioForPosition(position);
final float scrollX = syncWithViewPager.getScrollX();
final float scrollY = syncWithViewPager.getScrollY();
syncToViewPager.scrollTo((int) (scrollX * ratio), (int) scrollY);
}
}
private float calculateRatioForPosition(int position) {
final float syncToViewPagerWidth = syncToViewPager.getWidth();
final float syncWithViewPagerWidth = syncWithViewPager.getWidth();
final float syncToViewPagerElementWeight = syncToViewPager.getAdapter().getPageWidth(position);
final float syncWithViewPagerElementWeight = syncWithViewPager.getAdapter().getPageWidth(position);
final float syncToViewPagerElementsCount = (1.0f / syncToViewPagerElementWeight);
final float syncWithViewPagerElementsCount = (1.0f / syncWithViewPagerElementWeight);
final float syncToViewPagerElementWidth = syncToViewPagerWidth / syncToViewPagerElementsCount;
final float syncWithViewPagerElementWidth = syncWithViewPagerWidth / syncWithViewPagerElementsCount;
return syncToViewPagerElementWidth / syncWithViewPagerElementWidth;
}
#Override
public void onPageSelected(final int position) {
}
#Override
public void onPageScrollStateChanged(final int state) {
scrollState = state;
if (state == ViewPager.SCROLL_STATE_IDLE) {
syncToViewPager.setCurrentItem(syncWithViewPager.getCurrentItem(), false);
}
}
}
And finally init ViewPager's
#Bind(R.id.photoPreviewPager)
ViewPager photoPreviewPager;
#Bind(R.id.photoViewPager)
ViewPager photoViewPager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
final List<PhotoInfo> photoInfos = PhotoInfosProvider.generate();
final PhotoPreviewAdapter photoPreviewAdapter = new PhotoPreviewAdapter(getSupportFragmentManager(), photoInfos);
final PhotoViewAdapter photoViewAdapter = new PhotoViewAdapter(getSupportFragmentManager(), photoInfos);
photoPreviewPager.setAdapter(photoPreviewAdapter);
photoPreviewPager.addOnPageChangeListener(new OnSyncPageChangeListener(photoViewPager, photoPreviewPager));
photoViewPager.setAdapter(photoViewAdapter);
photoViewPager.setOffscreenPageLimit(photoPreviewAdapter.getSidePreviewCount() * 2 + 1);
photoViewPager.addOnPageChangeListener(new OnSyncPageChangeListener(photoPreviewPager, photoViewPager));
}
More detailed code is in repo

The LinearLayoutManager have a scrollToPositionWithOffset method that takes both the position and also the offset of the start of the item from the start of the RecyclerView, which seems like it would accomplish what you need.
You can use this image slider(https://github.com/jjhesk/LoyalNativeSlider) instead of the ViewPager .

First of all, you can use this google official example to create visual effect of pulling this view to center. You'll have ImageView over ViewPager for displaying animated appearing. When animation will be finished, make make your ImageView Gone and show requested image in ViewPager.