Scroll a ImageView on scroll of the RecyclerView

Scroll a ImageView on scroll of the RecyclerView - android

My requirement is scrolling a ImageView left and right on top of a list of data in the Recyclerview. When Recyclerview is scrolled up the ImageView will move towards right until list reaches to the end and vice versa.
I have tried but facing few complexity any suggestions and reference will be very helpful.Or any logic will also be appreciated.
The problem what I facing now is that not able to handle the values in the addOnScrollListener
Sharing my code in the github: Github Link
MainActivity Code:
Sharing few lines of code:
public class MainActivity extends AppCompatActivity implements View.OnClickListener, ClickEventLisener {
HorizontalScrollView v_scroll;
Button btn_left, btn_right;
int pos = 0;
int temppos = 0;
int initialpos = 0;
RecyclerView rv_recycler;
UserApapter adapter;
List<Users> user = new ArrayList<>();
Context mContext;
boolean isFirsttime = true;
ImageView iv_image;
String imageurl = "https://www.isometrix.com/wp-content/uploads/2017/03/featured-images-about.jpg";
int screenwidth = 0, imagewidth = 0;
int scroolby_val = 0;
#SuppressLint("ClickableViewAccessibility")
#RequiresApi(api = Build.VERSION_CODES.M)
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mContext = this;
iv_image = findViewById(R.id.iv_image);
v_scroll = findViewById(R.id.v_scroll);
btn_left = findViewById(R.id.btn_left);
btn_right = findViewById(R.id.btn_right);
rv_recycler = findViewById(R.id.rv_recycler);
btn_left.setOnClickListener(this);
btn_right.setOnClickListener(this);
v_scroll.setOnTouchListener(new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
return true;
}
});
filllist();
getScreenSize();
setupimage();
getleftscroll();
// when scrolled to the leftmost position the variables are initialized
v_scroll.setOnScrollChangeListener(new View.OnScrollChangeListener() {
#Override
public void onScrollChange(View view, int i, int i1, int i2, int i3) {
initialpos = i;
if (i == 0) {
temppos = 0;
} else {
}
}
});
///not able to understand how to handle the values
//handling the scroll
rv_recycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
getleftscroll();
if (dy > 0) {
temppos = temppos + scroolby_val;
v_scroll.scrollTo(temppos, 0);
Log.d("Scroll", "ScrollUp");
Log.d("temppos", "" + temppos);
} else {
if (initialpos != 0) {
temppos = temppos - scroolby_val;
v_scroll.scrollTo(temppos, 0);
Log.d("temppos1", "" + temppos);
Log.d("Scroll", "ScrollDown");
}
}
}
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
if (newState == AbsListView.OnScrollListener.SCROLL_STATE_FLING) {
// Do something
} else if (newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
// Do something
} else {
// Do something
}
}
});
}
private void getScreenSize() {
DisplayMetrics displayMetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
int height = displayMetrics.heightPixels;
int width = displayMetrics.widthPixels;
Log.d("ScreenWidth", "" + width);
screenwidth = width;
}
private void setupimage() {
Glide.with(mContext)
.asBitmap()
.load(imageurl)
.into(new SimpleTarget<Bitmap>() {
#Override
public void onResourceReady(Bitmap bitmap, Transition<? super Bitmap> transition) {
int w = bitmap.getWidth();
int h = bitmap.getHeight();
Log.d("ImageWitdh", "" + w);
iv_image.setImageBitmap(bitmap);
imagewidth = w;
}
});
}
/*
Logic I have implemented:calculated Imagewidth and screenwidth. Then minus it (imagewidth > screenwidth) and then divide it by the number of values in the array.
if the value is 0 then scrolling it by 1 per scroll or if the returned value is 3 then scrolling it by 3.
IOS team have done this way and working good for them but I am facing a minor issue here.
*/
private void getleftscroll() {
imagewidth = 2000;
if (imagewidth > screenwidth) {
int leftoutscreen = imagewidth - screenwidth;
scroolby_val = leftoutscreen / user.size();
if (scroolby_val == 0) {
scroolby_val = 1;
}
// temppos = 0;
Log.d("scroolby_val", "" + scroolby_val);
}
}
///button is just for demo purpose///
#Override
public void onClick(View v) {
if (v == btn_left) {
if (initialpos != 0) {
temppos = temppos - pos--;
v_scroll.scrollTo(temppos, 0);
Log.d("temppos", "" + temppos);
}
} else if (v == btn_right) {
temppos = temppos + pos++;
v_scroll.scrollTo(temppos, -temppos);
Log.d("temppos", "" + temppos);
}
}
private void filllist() {
user.clear();
for (int i = 0; i <= 300; i++) {
user.add(new Users(String.valueOf(i + 1), "name " + i));
}
inflateadapter();
}
private void inflateadapter() {
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
adapter = new UserApapter(this, R.layout.row_users, user, this);
rv_recycler.setLayoutManager(mLayoutManager);
rv_recycler.setAdapter(adapter);
}
#Override
public void Currentposition(int position) {
Log.d("Currentposition", "" + position);
if (position == user.size() - 1) {
if (scroolby_val == 1) {
Log.d("scroolby_val", "" + scroolby_val);
Log.d("Inside", "Inside");
// v_scroll.fullScroll(HorizontalScrollView.FOCUS_RIGHT);
// temppos = 1;
}
} else if (position == 0) {
temppos = 0;
}
pos = position;
}
#Override
public void ClickEventLisener(View view, int position) {
Toast.makeText(mContext, "" + position, Toast.LENGTH_SHORT).show();
}
}

Few things you may want to consider-
Don't use dy values from onScrolled callback directly to set scroll of v_scroll. There should be a logic to map scroll state of recycler view to the required scroll in v_scroll.
Don't use dy at all. Logic to set scroll of v_scroll should be based on the number of items in the list and the first/last visible child in it. (RecyclerView provides methods to get that.) You can run that logic from onScrolled callback.

Related

Trouble making a Firebase query

I am having trouble implementing an endless scroll in android using a recycler view. What I want is, essentially, something like instagram, that you scroll through a page endlessly.
I have a Firebase database with 10 items, and I want to show 3 items and charge the next two, then when you scroll through the next two items start loading the next 5 and so on. (You will see that most of this in the example is hardcoded).
I am having trouble making a Firebase query like this:
myRef.orderByChild("id").startAt(page*5 + "").endAt(5+page*5 + "")
what I would like to get then is at my current location the next 5 items with and id between - let's say - 5 and 10. However, when I do this:
myRef.orderByChild("id").startAt(page*5 + "").endAt(5+page*5 + "")
.getRef().addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
int i = 0;
for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
if(i == 5) break;
mDataset.add(postSnapshot.getValue(Card.class));
i++;
}
mAdapter = new CustomAdapter(mDataset);
mRecyclerView.setAdapter(mAdapter);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
all the postSnapshots return ids 1, 2, 3, 4, 5. Making the illusion of scrolling endlessly but charging the same 5 items every time.
Thanks
Edit:
EndlessScrollListener
public abstract class EndlessScrollListener extends RecyclerView.OnScrollListener {
private int mVisibleThreshold = 2,
mCurrentPage = 0,
mPreviousTotalItemCount = 0,
mStartingPageIndex = 0;
private boolean mLoading = true;
RecyclerView.LayoutManager mLayoutManager;
public EndlessScrollListener(){}
public EndlessScrollListener(LinearLayoutManager layoutManager){
mLayoutManager = layoutManager;
}
public EndlessScrollListener(int visibleThreshold){
mVisibleThreshold = visibleThreshold;
}
public int getLastVisibleItem(int[] lastVisibleItemPositions){
int maxSize = lastVisibleItemPositions[0];
for(int i = 1; i < lastVisibleItemPositions.length; ++i){
if(lastVisibleItemPositions[i] > maxSize)
maxSize = lastVisibleItemPositions[i];
}
return maxSize;
}
#Override
public void onScrolled(RecyclerView view, int dx, int dy){
int lastVisibleItemPosition = 0,
totalItemCount = mLayoutManager.getItemCount();
if (mLayoutManager instanceof LinearLayoutManager) {
lastVisibleItemPosition =
((LinearLayoutManager) mLayoutManager).findLastVisibleItemPosition();
}
if(totalItemCount < mPreviousTotalItemCount){
mCurrentPage = mStartingPageIndex;
mPreviousTotalItemCount = totalItemCount;
mLoading = totalItemCount == 0;
}
if(mLoading && totalItemCount > mPreviousTotalItemCount){
mLoading = false;
mPreviousTotalItemCount = totalItemCount;
}
if(!mLoading && (lastVisibleItemPosition + mVisibleThreshold) > totalItemCount){
mCurrentPage++;
onLoadMore(mCurrentPage, totalItemCount, view);
mLoading = true;
}
}
public abstract void onLoadMore(int page, int totalItemsCount, RecyclerView view);
public void resetState(){
mCurrentPage = mStartingPageIndex;
mPreviousTotalItemCount = 0;
mLoading = true;
}
}
In its activity
scrollListener = new EndlessScrollListener(mLayoutManager) {
#Override
public void onLoadMore(int page, int totalItemsCount, RecyclerView view) {
System.out.println("Dale... Page: " + page + " items: " + totalItemsCount);
loadData(page);
}
};

Not working Notifydatasetchange on RecyclerView with center selection Horizontal Scrollview?

Auto Scrolling is issue & also move to some specific position using code is difficult.
I am making two recyclerView dependent to each other with the Horizontal Scroll and center selection.
So my problem is using the method of Notifydatasetchanged and reseting recyclerView postion to 0 and it's scrolling selection range because it's returning wrong index...
When i want to get center selection index after changing data.
I am using below example to achieve this with some edits.
Get center visible item of RecycleView when scrolling
I need to change the data on scroll of First recyclerView Adapter to second recyclerView Adapter with data change.
But scrollview set the position in first position
I tried the notifyItemRangeChanged(int, int)
notifyItemRangeInserted(int, int) methods...
Detail Explanation : I am changing the type and reset the value of Look scrollview. I need to change the selected position of bottom scrollview. Specially I can't get the center position by changing data. Means I if i am notifying the adapter than index will remain as it is. I need to do work it like normal adapter after reset data.
Thanks in advance.
public void getRecyclerview_Type() {
final RecyclerView recyclerView_Type = (RecyclerView) findViewById(R.id.recycleView);
if (recyclerView_Type != null) {
recyclerView_Type.postDelayed(new Runnable() {
#Override
public void run() {
setTypeValue();
}
}, 300);
recyclerView_Type.postDelayed(new Runnable() {
#Override
public void run() {
// recyclerView_Type.smoothScrollToPosition(Type_Adapter.getItemCount() - 1);
setTypeValue();
}
}, 5000);
}
ViewTreeObserver treeObserver = recyclerView_Type.getViewTreeObserver();
treeObserver.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
#Override
public boolean onPreDraw() {
recyclerView_Type.getViewTreeObserver().removeOnPreDrawListener(this);
finalWidthDate = recyclerView_Type.getMeasuredWidth();
itemWidthDate = getResources().getDimension(R.dimen.item_dob_width_padding);
paddingDate = (finalWidthDate - itemWidthDate) / 2;
firstItemWidthDate = paddingDate;
allPixelsDate = 0;
final LinearLayoutManager dateLayoutManager = new LinearLayoutManager(getApplicationContext());
dateLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
recyclerView_Type.setLayoutManager(dateLayoutManager);
recyclerView_Type.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
synchronized (this) {
if (newState == RecyclerView.SCROLL_STATE_IDLE) {
calculatePositionAndScroll_Type(recyclerView);
}
}
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
allPixelsDate += dx;
}
});
if (mTypeBeanArrayList == null) {
mTypeBeanArrayList = new ArrayList<>();
}
getMedicationType();
Type_Adapter = new Medication_Type_RecyclerAdapter(Add_Reminder_medicationlook_Activity.this, mTypeBeanArrayList, (int) firstItemWidthDate);
recyclerView_Type.setAdapter(Type_Adapter);
Type_Adapter.setSelecteditem(Type_Adapter.getItemCount() - 1);
return true;
}
});
}
private void getMedicationType() {
for (int i = 0; i < mTypeBeanArrayList.size(); i++) {
Medication_TypeBean medication_typeBean = mTypeBeanArrayList.get(i);
Log.print("Image name :" +medication_typeBean.getType_image_name());
if (i == 0 || i == (mTypeBeanArrayList.size() - 1)) {
medication_typeBean.setType(VIEW_TYPE_PADDING);
} else {
medication_typeBean.setType(VIEW_TYPE_ITEM);
}
mTypeBeanArrayList.set(i, medication_typeBean);
}
}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
private void calculatePositionAndScroll_Type(RecyclerView recyclerView) {
int expectedPositionDate = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
if (expectedPositionDate == -1) {
expectedPositionDate = 0;
} else if (expectedPositionDate >= recyclerView.getAdapter().getItemCount() - 2) {
expectedPositionDate--;
}
scrollListToPosition_Type(recyclerView, expectedPositionDate);
}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
private void scrollListToPosition_Type(RecyclerView recyclerView, int expectedPositionDate) {
float targetScrollPosDate = expectedPositionDate * itemWidthDate + firstItemWidthDate - paddingDate;
float missingPxDate = targetScrollPosDate - allPixelsDate;
if (missingPxDate != 0) {
recyclerView.smoothScrollBy((int) missingPxDate, 0);
}
setTypeValue();
}
private void setTypeValue() {
int expectedPositionDateColor = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
int setColorDate = expectedPositionDateColor + 1;
Type_Adapter.setSelecteditem(setColorDate);
mTxt_type_name.setText(mTypeBeanArrayList.get(setColorDate).getMedication_type_name());
mSELECTED_TYPE_ID = setColorDate;
//NotifyLookChangetoType(setColorDate);
}
//Type Adapter
public class Medication_Type_RecyclerAdapter extends RecyclerView.Adapter<Medication_Type_RecyclerAdapter.ViewHolder> {
private ArrayList<Medication_TypeBean> medication_typeBeanArrayList;
private static final int VIEW_TYPE_PADDING = 1;
private static final int VIEW_TYPE_ITEM = 2;
private int paddingWidthDate = 0;
private Context mContext;
private int selectedItem = -1;
public Medication_Type_RecyclerAdapter(Context context, ArrayList<Medication_TypeBean> dateData, int paddingWidthDate) {
this.medication_typeBeanArrayList = dateData;
this.paddingWidthDate = paddingWidthDate;
this.mContext = context;
}
#Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == VIEW_TYPE_ITEM) {
final View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_medication_type,
parent, false);
return new ViewHolder(view);
} else {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_medication_type,
parent, false);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) view.getLayoutParams();
layoutParams.width = paddingWidthDate;
view.setLayoutParams(layoutParams);
return new ViewHolder(view);
}
}
#Override
public void onBindViewHolder(ViewHolder holder, int position) {
Medication_TypeBean medication_typeBean = mTypeBeanArrayList.get(position);
if (getItemViewType(position) == VIEW_TYPE_ITEM) {
// holder.mTxt_Type.setText(medication_typeBean.getMedication_type_name());
//holder.mTxt_Type.setVisibility(View.VISIBLE);
holder.mImg_medication.setVisibility(View.VISIBLE);
int d = R.drawable.ic_type_pill;
try {
//Due to Offline requirements we do code like this get the images from our res folder
if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_pill")) {
d = R.drawable.ic_type_pill;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_patch")) {
d = R.drawable.ic_type_patch;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_capsule")) {
d = R.drawable.ic_type_capsule;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_ring")) {
d = R.drawable.ic_type_ring;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_inhaler")) {
d = R.drawable.ic_type_inhaler;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_spray")) {
d = R.drawable.ic_type_spray;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_bottle")) {
d = R.drawable.ic_type_bottle;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_drop")) {
d = R.drawable.ic_type_drop;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_pessaries")) {
d = R.drawable.ic_type_pessaries;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_sachets")) {
d = R.drawable.ic_type_sachets;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_tube")) {
d = R.drawable.ic_type_tube;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_suppository")) {
d = R.drawable.ic_type_suppository;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_injaction")) {
d = R.drawable.ic_type_injaction;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_spoon")) {
d = R.drawable.ic_type_spoon;
} else if (medication_typeBean.getType_image_name().equalsIgnoreCase("ic_type_powder")) {
d = R.drawable.ic_type_powder;
} else {
d = R.drawable.ic_type_pill;
}
Bitmap icon = BitmapFactory.decodeResource(mContext.getResources(),
d);
holder.mImg_medication.setImageBitmap(icon);
} catch (Exception e) {
Log.print(e);
}
// BitmapDrawable ob = new BitmapDrawable(mContext.getResources(), icon);
// img.setBackgroundDrawable(ob);
// holder.mImg_medication.setBackground(ob);
// Log.print("Type Adapter", "default " + position + ", selected " + selectedItem);
if (position == selectedItem) {
Log.print("Type adapter", "center" + position);
// holder.mTxt_Type.setTextColor(Color.parseColor("#76FF03"));
//holder.mImg_medication.setColorFilter(Color.GREEN);
// holder.mTxt_Type.setTextSize(35);
holder.mImg_medication.getLayoutParams().height = (int) mContext.getResources().getDimension(R.dimen.item_dob_width) + 10;
holder.mImg_medication.getLayoutParams().width = (int) mContext.getResources().getDimension(R.dimen.item_dob_width) + 10;
} else {
holder.mImg_medication.getLayoutParams().height = (int) mContext.getResources().getDimension(R.dimen.item_dob_width) - 10;
holder.mImg_medication.getLayoutParams().width = (int) mContext.getResources().getDimension(R.dimen.item_dob_width) - 10;
// holder.mTxt_Type.setTextColor(Color.WHITE);
//holder.mImg_medication.setColorFilter(null);
// holder.mTxt_Type.setVisibility(View.INVISIBLE);
// holder.mTxt_Type.setTextSize(18);
// holder.mImg_medication.getLayoutParams().height = 70;
// holder.mImg_medication.getLayoutParams().width = 70;
}
} else {
holder.mImg_medication.getLayoutParams().height = (int) mContext.getResources().getDimension(R.dimen.item_dob_width) - 10;
holder.mImg_medication.getLayoutParams().width = (int) mContext.getResources().getDimension(R.dimen.item_dob_width) - 10;
// holder.mTxt_Type.setVisibility(View.INVISIBLE);
holder.mImg_medication.setVisibility(View.INVISIBLE);
}
}
public void setSelecteditem(int selecteditem) {
this.selectedItem = selecteditem;
notifyDataSetChanged();
if (medication_lookBeanArrayList != null && Look_Adapter != null) {
NotifyLookChangetoType(selecteditem);
}
}
public int getSelecteditem() {
return selectedItem;
}
#Override
public int getItemCount() {
return medication_typeBeanArrayList.size();
}
#Override
public int getItemViewType(int position) {
Medication_TypeBean medication_typeBean = medication_typeBeanArrayList.get(position);
if (medication_typeBean.getType() == VIEW_TYPE_PADDING) {
return VIEW_TYPE_PADDING;
} else {
return VIEW_TYPE_ITEM;
}
}
public class ViewHolder extends RecyclerView.ViewHolder {
//public TextView mTxt_Type;
public ImageView mImg_medication;
public ViewHolder(View itemView) {
super(itemView);
// mTxt_Type = (TextView) itemView.findViewById(R.id.mTxt);
mImg_medication = (ImageView) itemView.findViewById(R.id.mImg_medication);
}
}
}
//Type Adapter ends ************************************************

I am not sure I get you properly but you want to change the data of one recyclerview and reset the value of other recyclerview
Try using recyclerView.scrollToPosition(INDEX_YOU_WANT_TO_SCROLL_TO);
IF YOU WANT TO ACHIEVE THE CENTER POSTION OF THE DATA USE
recyclerview.scrollToPosition(arraylist.size()/2);
arrayList in which your drawable data is stored

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;
}

Detect the ListView scroll direction and distance

Is there a way to get a listview's scroll distance, and exactly how far in pixel it scrolls?
Thank you

See this snippet written by me. It can calculate how far in pixel it scrolls, and listen scroll change.
/**
* Created by mariotaku on 14/10/22.
*/
public class ListScrollDistanceCalculator implements OnScrollListener {
private ScrollDistanceListener mScrollDistanceListener;
private boolean mListScrollStarted;
private int mFirstVisibleItem;
private int mFirstVisibleHeight;
private int mFirstVisibleTop, mFirstVisibleBottom;
private int mTotalScrollDistance;
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if (view.getCount() == 0) return;
switch (scrollState) {
case SCROLL_STATE_IDLE: {
mListScrollStarted = false;
break;
}
case SCROLL_STATE_TOUCH_SCROLL: {
final View firstChild = view.getChildAt(0);
mFirstVisibleItem = view.getFirstVisiblePosition();
mFirstVisibleTop = firstChild.getTop();
mFirstVisibleBottom = firstChild.getBottom();
mFirstVisibleHeight = firstChild.getHeight();
mListScrollStarted = true;
mTotalScrollDistance = 0;
break;
}
}
}
public int getTotalScrollDistance() {
return mTotalScrollDistance;
}
#Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (totalItemCount == 0 || !mListScrollStarted) return;
final View firstChild = view.getChildAt(0);
final int firstVisibleTop = firstChild.getTop(), firstVisibleBottom = firstChild.getBottom();
final int firstVisibleHeight = firstChild.getHeight();
final int delta;
if (firstVisibleItem > mFirstVisibleItem) {
mFirstVisibleTop += mFirstVisibleHeight;
delta = firstVisibleTop - mFirstVisibleTop;
} else if (firstVisibleItem < mFirstVisibleItem) {
mFirstVisibleBottom -= mFirstVisibleHeight;
delta = firstVisibleBottom - mFirstVisibleBottom;
} else {
delta = firstVisibleBottom - mFirstVisibleBottom;
}
mTotalScrollDistance += delta;
if (mScrollDistanceListener != null) {
mScrollDistanceListener.onScrollDistanceChanged(delta, mTotalScrollDistance);
}
mFirstVisibleTop = firstVisibleTop;
mFirstVisibleBottom = firstVisibleBottom;
mFirstVisibleHeight = firstVisibleHeight;
mFirstVisibleItem = firstVisibleItem;
}
public void setScrollDistanceListener(ScrollDistanceListener listener) {
mScrollDistanceListener = listener;
}
public static interface ScrollDistanceListener {
void onScrollDistanceChanged(int delta, int total);
}
}

I think that getScrollY() may help you:
Return the scrolled top position of this view. This is the top edge of the displayed part of your view.
See http://developer.android.com/reference/android/view/View.html#getScrollY()

Develop Reference

The Android operating system is a mobile operating system that was developed by Google (GOOGL?) to be primarily used for touchscreen devices, cell phones, and tablets.

Scroll a ImageView on scroll of the RecyclerView - android

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