I am attempting to create an animation in my RecyclerView rows with a Helper class that extends ItemTouchHelper.Callback.
The default "swipe" behaviour with ItemTouchHelper is that if a row is swiped with sufficient velocity, it disappears from view (i.e. swipe-to-dimiss). In my case, I want to create an animation that causes the row to bounce straight back if such an event takes place.
I have been able to create a ValueAnimator that animates the row back into view if it is swiped off screen. However, the problem is that I cannot get the parent ItemTouchHelper class to recognise that the x values it has stored have changed from the width of the row (so that it is completely offscreen) to 0 (so that it is back on screen).
This means that whenever I go to interact with the row after it has completed my custom animation, it behaves as if the row is still off screen, even though it is fully visible. This usually means that pressing it means the row jumps from an X position of 0 to an X position of the row width, and so animates back in again from the screen's edge. It does this a couple of times before it fully resets and behaves normally again.
This video will help show the problem. As the first two swipes are not flings off-screen, the default behaviour works. After the row is swiped off screen however and bounces back, tapping the row shows it pinging back in from the right edge:
Here is the code I use to conduct the animation:
public class CustomItemTouchHelper extends ItemTouchHelper.Callback {
private RecoverAnimation ra;
private boolean animatorRunning;
//...
#Override
public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
final float per = (dX/viewHolder.itemView.getWidth());
if (per > 0.8F && !animatorRunning && !isCurrentlyActive) {
ra = new RecoverAnimation(c, recyclerView, viewHolder, ItemTouchHelper.ANIMATION_TYPE_SWIPE_CANCEL, actionState, dX, dY, 0, 0);
ra.start();
} else {
getDefaultUIUtil().onDraw(c, recyclerView, viewHolder.itemView, dX, dY, actionState, isCurrentlyActive);
}
}
//...
Note that this inner class, RecoverAnimation, is pulled from the ItemTouchHelper source code:
private class RecoverAnimation implements AnimatorListenerCompat {
final float mStartDx;
final float mStartDy;
final float mTargetX;
final float mTargetY;
final Canvas mCanvas;
final RecyclerView mRecyclerView;
final RecyclerView.ViewHolder mViewHolder;
final int mActionState;
private final ValueAnimatorCompat mValueAnimator;
float mX;
float mY;
// if user starts touching a recovering view, we put it into interaction mode again,
// instantly.
boolean mOverridden = false;
private boolean mEnded = false;
private float mFraction;
public RecoverAnimation(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder,
int actionState, float startDx, float startDy, float targetX, float targetY) {
mRecyclerView = recyclerView;
mCanvas = c;
mActionState = actionState;
mViewHolder = viewHolder;
mStartDx = startDx;
mStartDy = startDy;
mTargetX = targetX;
mTargetY = targetY;
mValueAnimator = AnimatorCompatHelper.emptyValueAnimator();
mValueAnimator.addUpdateListener(
new AnimatorUpdateListenerCompat() {
#Override
public void onAnimationUpdate(ValueAnimatorCompat animation) {
setFraction(animation.getAnimatedFraction());
update();
}
});
mValueAnimator.setTarget(viewHolder.itemView);
mValueAnimator.addListener(this);
setFraction(0f);
}
public void setDuration(long duration) {
mValueAnimator.setDuration(duration);
}
public void start() {
animatorRunning = true;
mViewHolder.setIsRecyclable(false);
mValueAnimator.start();
}
public void cancel() {
mValueAnimator.cancel();
}
public void setFraction(float fraction) {
mFraction = fraction;
}
/**
* We run updates on onDraw method but use the fraction from animator callback.
* This way, we can sync translate x/y values w/ the animators to avoid one-off frames.
*/
public void update() {
if (mStartDx == mTargetX) {
mX = ViewCompat.getTranslationX(mViewHolder.itemView);
} else {
mX = mStartDx + mFraction * (mTargetX - mStartDx);
}
if (mStartDy == mTargetY) {
mY = ViewCompat.getTranslationY(mViewHolder.itemView);
} else {
mY = mStartDy + mFraction * (mTargetY - mStartDy);
}
getDefaultUIUtil().onDraw(mCanvas, mRecyclerView, mViewHolder.itemView, mX, mY, mActionState, false);
}
#Override
public void onAnimationStart(ValueAnimatorCompat animation) {
}
#Override
public void onAnimationEnd(ValueAnimatorCompat animation) {
animatorRunning = false;
mEnded = true;
getDefaultUIUtil().onDraw(mCanvas, mRecyclerView, mViewHolder.itemView, 0, 0, ItemTouchHelper.ACTION_STATE_IDLE, false);
getDefaultUIUtil().clearView(mViewHolder.itemView);
}
#Override
public void onAnimationCancel(ValueAnimatorCompat animation) {
setFraction(1f); //make sure we recover the view's state.
}
#Override
public void onAnimationRepeat(ValueAnimatorCompat animation) {
}
}
Is there anything I can do to counteract this issue, or is it simply not possible (yet)?
Following solution will bounce back recyclerview item without implementing your custom RecoverAnimation class.
public class CustomItemTouchHelper extends ItemTouchHelper.Callback {
private RecoverAnimation ra;
private boolean animatorRunning;
private boolean swipeBack = false;
//...
#Override
public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
recyclerView.setOnTouchListener(new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event)
{
if(event.getAction() == MotionEvent.ACTION_UP || event.getAction() == MotionEvent.ACTION_CANCEL)
{
swipeBack = true;
}
else
{
swipeBack = false;
}
return false;
}
});
}
#Override
public int convertToAbsoluteDirection(int flags, int layoutDirection) {
return swipeBack ? 0 : super.convertToAbsoluteDirection(flags, layoutDirection);
}
//...
Related
i have a problem figuring out how to give cardViews temporarily elevation on drag. I use a recycler view with cardViews and this is my itemtouchhelper:
class ListTouchHelper extends ItemTouchHelper.Callback {
private final ActionCompletionContract contract;
public ListTouchHelper(ActionCompletionContract contract) {
this.contract = contract;
}
#Override
public int getMovementFlags(#NonNull RecyclerView recyclerView, #NonNull RecyclerView.ViewHolder viewHolder) {
int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
int swipeFlags = ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
return makeMovementFlags(dragFlags, swipeFlags);
}
#Override
public boolean onMove(#NonNull RecyclerView recyclerView, #NonNull RecyclerView.ViewHolder viewHolder, #NonNull RecyclerView.ViewHolder target) {
contract.onViewMoved(viewHolder.getAdapterPosition(), target.getAdapterPosition());
return true;
}
#Override
public void onSwiped(#NonNull RecyclerView.ViewHolder viewHolder, int direction) {
if (direction == ItemTouchHelper.LEFT) {
contract.onViewSwipedLeft(viewHolder.getAdapterPosition());
} else if (direction == ItemTouchHelper.RIGHT) {
contract.onViewSwipedRight(viewHolder.getAdapterPosition());
}
}
public interface ActionCompletionContract {
void onViewMoved(int oldPosition, int newPosition);
void onViewSwipedLeft(int position);
void onViewSwipedRight(int position);
}
}
I have managed to give it temporarily elevation with:
Which resulted in: (the shadows are somehow clipped?)
However, once the view is just slightly moved, the elevation disappears:
My question is: how do i get the elevation (including shadows) when the cards are being dragged?
Thanks in advance!
#LivinTheNoobLife in your solution you are using the ViewPropertyAnimator, but you are not setting any translation to it, hence, no animations will be applied.
This is my solution with a properly working floating animation:
class DragHelper extends ItemTouchHelper.Callback {
private boolean cardPicked = true;
private boolean reset = false;
#Override
public void onChildDraw(#NonNull Canvas c, #NonNull RecyclerView recyclerView, #NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
// elevate only when picked for the first time
if (cardPicked) {
ViewPropertyAnimator animator = viewHolder.itemView.animate();
animator.translationZ(16);
animator.setDuration(200);
animator.setInterpolator(new AccelerateDecelerateInterpolator());
animator.start();
cardPicked = false;
}
// when your item is not floating anymore
if (reset){
ViewPropertyAnimator animator = viewHolder.itemView.animate();
animator.translationZ(0);
animator.setDuration(200);
animator.setInterpolator(new AccelerateInterpolator());
animator.start();
cardPicked = true;
reset = false;
}
super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}
// As the doc says
// Called by the ItemTouchHelper when the user interaction with an element is over and it also completed its animation.
#Override
public void clearView(#NonNull RecyclerView recyclerView, #NonNull RecyclerView.ViewHolder viewHolder) {
super.clearView(recyclerView, viewHolder);
// interaction is over, time to reset our elevation
reset = true;
}
}
Ok so I solved it, kindof. I think for some other reason its not working by default, however I managed to write a workaround.
private boolean first = true; //first draw of cardView?
private boolean last = false; //last draw of cardView?
#Override
public void onChildDraw(#NonNull Canvas c, #NonNull RecyclerView recyclerView, #NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
//add elevation on first draw
if (first) {
ViewPropertyAnimator animator = viewHolder.itemView.animate();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) { //consider SDK version
viewHolder.itemView.setTranslationZ(7);
animator.start();
}
first = false;
}
//remove translationZ in last edit
if (last) {
ViewPropertyAnimator animator = viewHolder.itemView.animate();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) { //consider SDK version
viewHolder.itemView.setTranslationZ(0);
animator.start();
}
//reset values
last=false;
first=true;
}
super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}
#Override
public void clearView(#NonNull RecyclerView recyclerView, #NonNull RecyclerView.ViewHolder viewHolder) {
super.clearView(recyclerView, viewHolder);
last = true; //only one more OnChildDrawWillBeCalled
}
The above code is added to your ItemTouchHelper.Callback and all should work.
The basic idea is to manually control the drawing of the translationz.
For that I figure out when is the first canvas drawn, and when the last, whereas the cancas will show the shadow.
Maxbe one more comment: the ViewPropertyAnimator in combination with the xml layout file is incredibly unintuitive and buggy, so if you can avoided I would reccomend to do so, and instead try programmatically animating the view changes and effects.
Hope this can help someone.
I have a list view with different item types: header, folder and file like this:
Now I 'd like to implement drag file item and drop it into folder item and get the source and target position.I don't want to change the target position (rearrange) while dragging like some drag sort list view libraries.
Is there any suggestion to start with?
Switching your ListView to RecyclerView will make things a lot easier.
You can find the whole article on Styling Android and the whole code here.
This code uses OnItemTouchListener to detect when an item should be dragged. There is an ImageView above the RecyclerView with an image of the item being moved to cheaply animate it.
The OnItemTouckListener (DragController.java):
public class DragController implements RecyclerView.OnItemTouchListener {
private RecyclerView recyclerView;
private ImageView overlay;
private final GestureDetectorCompat gestureDetector;
private boolean isDragging = false;
public DragController(RecyclerView recyclerView, ImageView overlay) {
this.recyclerView = recyclerView;
this.overlay = overlay;
GestureDetector.SimpleOnGestureListener longClickGestureListener = new GestureDetector.SimpleOnGestureListener() {
#Override
public void onLongPress(MotionEvent e) {
super.onLongPress(e);
isDragging = true;
dragStart(e.getX(), e.getY());
}
};
this.gestureDetector = new GestureDetectorCompat(recyclerView.getContext(), longClickGestureListener);
}
#Override
public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {
if (isDragging) {
return true;
}
gestureDetector.onTouchEvent(e);
return false;
}
#Override
public void onTouchEvent(RecyclerView rv, MotionEvent e) {
int x = (int) e.getX();
int y = (int) e.getY();
View view = recyclerView.findChildViewUnder(x, y);
if (e.getAction() == MotionEvent.ACTION_UP) {
dragEnd(view);
isDragging = false;
} else {
drag(y, view);
}
}
Starting and ending the drag (DragController.java):
private boolean isFirst = true;
private static final int ANIMATION_DURATION = 100;
private int draggingItem = -1;
private float startY = 0f;
private Rect startBounds = null;
private void dragStart(float x, float y) {
View draggingView = recyclerView.findChildViewUnder(x, y);
View first = recyclerView.getChildAt(0);
isFirst = draggingView == first;
startY = (y - draggingView.getTop());
paintViewToOverlay(draggingView);
overlay.setTranslationY(y - startY);
draggingView.setVisibility(View.INVISIBLE);
draggingItem = recyclerView.indexOfChild(draggingView);
startBounds = new Rect(draggingView.getLeft(), draggingView.getTop(), draggingView.getRight(), draggingView.getBottom());
}
private void drag(int y, View view) {
overlay.setTranslationY(y - startY);
}
private void dragEnd(View view) {
overlay.setImageBitmap(null);
view.setVisibility(View.VISIBLE);
view.setTranslationY(overlay.getTranslationY() - view.getTop());
view.animate().translationY(0f).setDuration(ANIMATION_DURATION).start();
}
private void paintViewToOverlay(View view) {
Bitmap bitmap = Bitmap.createBitmap(view.getWidth(), view.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
view.draw(canvas);
overlay.setImageBitmap(bitmap);
overlay.setTop(0);
}
The code is written by Mark Allison on StylingAndroid.
Edit:
But I don't know how to get the position of item when dragging is end
The answer is located in part 7 on Styling Android.
View view = recyclerView.findChildViewUnder(0, y);
And how can I disable drag on Folder and Header item? Just allow dragging File item?
You can do this by using multiple ViewTypes (file, folder & header). Then you can use getItemViewType in DragController to start the movement only for files.
Use RecyclerView and ItemTouchHelper.SimpleCallback.
You can setup it like that in your activity:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list); // Your layout with RecyclerView
RecyclerView itemRecyclerView = findViewById(R.id.itemRecyclerView);
LinearLayoutManager itemLayoutManager = new LinearLayoutManager(this);
itemRecyclerView.setLayoutManager(itemLayoutManager);
itemAdapter = new ItemAdapter(); // Your adapter which extends RecyclerView.Adapter
itemRecyclerView.setAdapter(itemAdapter);
itemRecyclerView.setHasFixedSize(true);
itemDragAndDropCallback = new ItemDragAndDropCallback(this, itemRecyclerView);
// Your class which extends ItemTouchHelper.SimpleCallback
// It will be shown in the next code sample
new ItemTouchHelper(itemDragAndDropCallback)
.attachToRecyclerView(itemRecyclerView);
}
You can use default functionality for item dragging provided by ItemTouchHelper.SimpleCallback.
The following class will demonstrate changing the background color of a folder. An item will be dropped into that folder.
class ItemDragAndDropCallback extends ItemTouchHelper.SimpleCallback {
ItemDragAndDropCallback() {
// Choose drag and swipe directions
// Up and down is chosen for dragging
// Right and left is chosen for swiping
super(ItemTouchHelper.UP | ItemTouchHelper.DOWN, ItemTouchHelper.RIGHT | ItemTouchHelper.LEFT);
}
#Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
// You can reorder items here
// Do nothing in your case
return true;
}
#Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
// You can react for swiping items here
// Do nothing in your case
}
// An item will be dropped into this folder
private View folder;
#Override
public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
super.onSelectedChanged(viewHolder, actionState);
if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) {
// Here you are notified that the drag operation began
if (folder != null) {
folder.setBackgroundResource(0); // Clear former folder background
}
} else if (actionState == ItemTouchHelper.ACTION_STATE_IDLE) {
// Here you are notified that the last operation ended
if (folder != null) {
// Set folder background to a color indicating
// that an item was dropped into it
folder.setBackgroundColor(
ContextCompat.getColor(
recyclerView.getContext(), android.R.color.holo_green_dark
)
);
}
}
}
#Override
public void onChildDraw(
Canvas c,
RecyclerView recyclerView,
RecyclerView.ViewHolder viewHolder,
float dX,
float dY,
int actionState,
boolean isCurrentlyActive
) {
if (actionState == ItemTouchHelper.ACTION_STATE_DRAG && isCurrentlyActive) {
// Here you are notified that the drag operation is in progress
if (folder != null) {
folder.setBackgroundResource(0); // Clear former folder background
}
float itemActualPosition = viewHolder.itemView.getTop() + dY;
// Find folder under dragged item
for (int i = 0; i < recyclerView.getChildCount(); i++) {
folder = recyclerView.getChildAt(i);
// Exclude dragged item from detection
if (!folder.equals(viewHolder.itemView)) {
// Accept folder which encloses item position
if (folder.getTop() < itemActualPosition && itemActualPosition < folder.getBottom()) {
// Set folder background to a color indicating
// that an item will be dropped into it upon release
folder.setBackgroundColor(
ContextCompat.getColor(
recyclerView.getContext(), android.R.color.holo_green_light
)
);
break;
}
}
}
}
super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}
}
When you drag an item over folders then the folder's background under the item will be light green.
When you drop the item into a folder then its background will be dark green.
I made a custom LayoutManager to smooth scroll after clicking a left or right button. Everything works when scrolling left only! For right, computeScrollVectorForPosition never event gets called. What gives? I've tried setting mReverseLayout when going right, but that hasn't help. Anything I'm not doing/overlooking?
public class SmoothScrollLayoutManager extends LinearLayoutManager {
private static final float MILLISECONDS_PER_INCH = 50f;
private Context context;
public boolean shouldGoRight = false;
public SmoothScrollLayoutManager(Context context, int orientation, boolean reverseLayout) {
super(context, orientation, reverseLayout);
this.context = context;
}
#Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
LinearSmoothScroller smoothScroller = new LinearSmoothScroller(context) {
#Override
public PointF computeScrollVectorForPosition(int targetPosition) {
if (getChildCount() == 0) {
return null;
}
final int firstChildPos = getPosition(getChildAt(0));
final int direction = targetPosition < firstChildPos != shouldGoRight ? -1 : 1;
return new PointF(direction, 0);
}
#Override
protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
}
};
smoothScroller.setTargetPosition(position);
startSmoothScroll(smoothScroller);
}
}
comupteScrollVectorForPosition is only called to find out the direction into which the LinearSmoothScroller has to scroll to eventually find the element. If the LinearSmoothScroller already thinks to know where the element is, it will not call this function. This is the case for elements that are already loaded to be shown, like your elements to the right.
I implemented a collapsingtoolbar layout with a recyclerview as shown in the sample code attached. My issue is that, when I fling the list downward, it does not go all the way to the top.
What happens is that, the scrolling stops right at the point where the AppBarLayout is supposed to end.
The effect that I want is upon flinging the list downward, the list will go all the way to the top AND reveal/expand the AppBarLayout
My minSdk is 14. Any help or suggestion is greatly appreciated.
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.AppBarLayout>
<android.support.design.widget.CollapsingToolbarLayout
app:layout_scrollFlags="scroll|exitUntilCollapsed">
<LinearLayout
app:layout_collapseMode="parallax">
//some elements
</LinearLayout>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.v7.widget.RecyclerView
app:layout_behavior="#string/appbar_scrolling_view_behavior"/> //value android.support.design.widget.AppBarLayout$ScrollingViewBehavior
<android.support.v7.widget.Toolbar
app:popupTheme="#style/AppTheme.PopupOverlay"
app:layout_collapseMode="parallax" />
I had similar problem and I used a simple trick to expand AppBarLayout when RecyclerView fling to top (you need to have support library >= 23.x.x)
mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
if (newState == RecyclerView.SCROLL_STATE_IDLE) {
int firstVisiblePosition = linearLayoutManager.findFirstCompletelyVisibleItemPosition();
if (firstVisiblePosition == 0) {
mAppBarLayout.setExpanded(true, true);
}
}
}
});
You can fully expand or collapse the App Bar with the setExpanded() method. One implementation could involve overriding dispatchTouchEvent() in your Activity class, and auto-collapsing/expanding your App Bar based on whether it is collapsed past the halfway point:
#Override
public boolean dispatchTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_UP) {
float per = Math.abs(mAppBarLayout.getY()) / mAppBarLayout.getTotalScrollRange();
boolean setExpanded = (per <= 0.5F);
mAppBarLayout.setExpanded(setExpanded, true);
}
return super.dispatchTouchEvent(event);
}
In respect to automatically scrolling to the last position on a fling, I have put some code on GitHub that shows how to programmatically smooth scroll to a specific location that may help. Calling a scroll to list.size() - 1 on a fling for instance could replicate the behaviour. Parts of this code by the way are adapted from the StylingAndroid and Novoda blogs:
public class RecyclerLayoutManager extends LinearLayoutManager {
private AppBarManager mAppBarManager;
private int visibleHeightForRecyclerView;
public RecyclerLayoutManager(Context context) {
super(context);
}
#Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
View firstVisibleChild = recyclerView.getChildAt(0);
final int childHeight = firstVisibleChild.getHeight();
int distanceInPixels = ((findFirstVisibleItemPosition() - position) * childHeight);
if (distanceInPixels == 0) {
distanceInPixels = (int) Math.abs(firstVisibleChild.getY());
}
//Called Once
if (visibleHeightForRecyclerView == 0) {
visibleHeightForRecyclerView = mAppBarManager.getVisibleHeightForRecyclerViewInPx();
}
//Subtract one as adapter position 0 based
final int visibleChildCount = visibleHeightForRecyclerView/childHeight - 1;
if (position <= visibleChildCount) {
//Scroll to the very top and expand the app bar
position = 0;
mAppBarManager.expandAppBar();
} else {
mAppBarManager.collapseAppBar();
}
SmoothScroller smoothScroller = new SmoothScroller(recyclerView.getContext(), Math.abs(distanceInPixels), 1000);
smoothScroller.setTargetPosition(position);
startSmoothScroll(smoothScroller);
}
public void setAppBarManager(AppBarManager appBarManager) {
mAppBarManager = appBarManager;
}
private class SmoothScroller extends LinearSmoothScroller {
private static final int TARGET_SEEK_SCROLL_DISTANCE_PX = 10000;
private final float distanceInPixels;
private final float duration;
public SmoothScroller(Context context, int distanceInPixels, int duration) {
super(context);
this.distanceInPixels = distanceInPixels;
float millisecondsPerPx = calculateSpeedPerPixel(context.getResources().getDisplayMetrics());
this.duration = distanceInPixels < TARGET_SEEK_SCROLL_DISTANCE_PX ?
(int) (Math.abs(distanceInPixels) * millisecondsPerPx) : duration;
}
#Override
public PointF computeScrollVectorForPosition(int targetPosition) {
return RecyclerLayoutManager.this
.computeScrollVectorForPosition(targetPosition);
}
#Override
protected int calculateTimeForScrolling(int dx) {
float proportion = (float) dx / distanceInPixels;
return (int) (duration * proportion);
}
}
}
Edit:
AppBarManager in the above code snippet refers to an interface used to communicate with the AppBarLayout in an Activity. Collapse/expand app bar methods do just that, with animations. The final method is used to calculate the number of RecyclerView rows visible on screen:
AppBarManager.java
public interface AppBarManager {
void collapseAppBar();
void expandAppBar();
int getVisibleHeightForRecyclerViewInPx();
}
MainActivity.java
public class MainActivity extends AppCompatActivity implements AppBarManager{
#Override
public void collapseAppBar() {
mAppBarLayout.setExpanded(false, true);
}
#Override
public void expandAppBar() {
mAppBarLayout.setExpanded(true, true);
}
#Override
public int getVisibleHeightForRecyclerViewInPx() {
if (mRecyclerFragment == null) mRecyclerFragment =
(RecyclerFragment) getSupportFragmentManager().findFragmentByTag(RecyclerFragment.TAG);
int windowHeight, appBarHeight, headerViewHeight;
windowHeight = getWindow().getDecorView().getHeight();
appBarHeight = mAppBarLayout.getHeight();
headerViewHeight = mRecyclerFragment.getHeaderView().getHeight();
return windowHeight - (appBarHeight + headerViewHeight);
}
I'm a newbie in Android development, and I would just like to know a little bit about the Scroller widget (android.widget.Scroller). How does it animate the view? Can the Animation object, if it exists, be accessed? If so, how? I've read the source code, but could find no clues, or maybe I'm too new?
I just wanted to do some operations after a Scroller finishes scrolling, something like
m_scroller.getAnimation().setAnimationListener(...);
The Scroller widget doesn't actually do much of the work at all for you. It doesn't fire any callbacks, it doesn't animate anything, it just responds to various method calls.
So what good is it? Well, it does all of the calculation for e.g. a fling for you, which is handy. So what you'd generally do is create a Runnable that repeatedly asks the Scroller, "What should my scroll position be now? Are we done flinging yet?" Then you repost that runnable on a Handler (usually on the View) until the fling is done.
Here's an example from a Fragment I'm working on right now:
private class Flinger implements Runnable {
private final Scroller scroller;
private int lastX = 0;
Flinger() {
scroller = new Scroller(getActivity());
}
void start(int initialVelocity) {
int initialX = scrollingView.getScrollX();
int maxX = Integer.MAX_VALUE; // or some appropriate max value in your code
scroller.fling(initialX, 0, initialVelocity, 0, 0, maxX, 0, 10);
Log.i(TAG, "starting fling at " + initialX + ", velocity is " + initialVelocity + "");
lastX = initialX;
getView().post(this);
}
public void run() {
if (scroller.isFinished()) {
Log.i(TAG, "scroller is finished, done with fling");
return;
}
boolean more = scroller.computeScrollOffset();
int x = scroller.getCurrX();
int diff = lastX - x;
if (diff != 0) {
scrollingView.scrollBy(diff, 0);
lastX = x;
}
if (more) {
getView().post(this);
}
}
boolean isFlinging() {
return !scroller.isFinished();
}
void forceFinished() {
if (!scroller.isFinished()) {
scroller.forceFinished(true);
}
}
}
The details of using Scroller.startScroll should be similar.
like Bill Phillips said, Scroller is just an Android SDK class helping with calculating scrolling positions. I have a full working example here:
public class SimpleScrollableView extends TextView {
private Scroller mScrollEventChecker;
private int mLastFlingY;
private float mLastY;
private float mDeltaY;
public SimpleScrollableView(Context context) {
this(context, null, 0);
}
public SimpleScrollableView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public SimpleScrollableView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
#Override
public boolean onTouchEvent(MotionEvent event) {
if (mScrollEventChecker != null && !mScrollEventChecker.isFinished()) {
return super.onTouchEvent(event);
}
final int action = event.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
mLastY = event.getY();
return true;
case MotionEvent.ACTION_MOVE:
int movingDelta = (int) (event.getY() - mLastY);
mDeltaY += movingDelta;
offsetTopAndBottom(movingDelta);
invalidate();
return true;
case MotionEvent.ACTION_UP:
mScrollEventChecker = new Scroller(getContext());
mScrollEventChecker.startScroll(0, 0, 0, (int) -mDeltaY, 1000);
post(new Runnable() {
#Override
public void run() {
if (mScrollEventChecker.computeScrollOffset()) {
int curY = mScrollEventChecker.getCurrY();
int delta = curY - mLastFlingY;
offsetTopAndBottom(delta); // this is the method make this view move
invalidate();
mLastFlingY = curY;
post(this);
} else {
mLastFlingY = 0;
mDeltaY = 0;
}
}
});
return super.onTouchEvent(event);
}
return super.onTouchEvent(event);
}
}
The demo custom view above will scroll back to original position after the user release the view. When user release the view, then startScroll() method is invoked and we can know what the distance value should be for every single message post.
Full working example: Github repository
Great answer above. Scroller#startScroll(...) indeed works the same way.
For example, the source for a custom scrolling TextView at:
http://bear-polka.blogspot.com/2009/01/scrolltextview-scrolling-textview-for.html
Sets a Scroller on a TextView using TextView#setScroller(Scroller).
The source for the SDK's TextView at:
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/2.2_r1.1/android/widget/TextView.java#TextView.0mScroller
Shows that TextView#setScroller(Scroller) sets a class field which is used in situations like bringPointIntoView(int) where Scroller#scrollTo(int, int, int, int) is called.
bringPointIntoView() adjusts mScrollX and mScrollY (with some SDK fragmentation code), then calls invalidate(). The point of all this is that mScrollX and mScrollY are used in methods like onPreDraw(...) to affect the position of the drawn contents of the view.
We can extend the Scroller class then intercept corresponding animation start methods to mark that was started, after computeScrollOffset() return false which means animation finished's value, we inform by a Listener to caller :
public class ScrollerImpl extends Scroller {
...Constructor...
private boolean mIsStarted;
private OnFinishListener mOnFinishListener;
#Override
public boolean computeScrollOffset() {
boolean result = super.computeScrollOffset();
if (!result && mIsStarted) {
try { // Don't let any exception impact the scroll animation.
mOnFinishListener.onFinish();
} catch (Exception e) {}
mIsStarted = false;
}
return result;
}
#Override
public void startScroll(int startX, int startY, int dx, int dy) {
super.startScroll(startX, startY, dx, dy);
mIsStarted = true;
}
#Override
public void startScroll(int startX, int startY, int dx, int dy, int duration) {
super.startScroll(startX, startY, dx, dy, duration);
mIsStarted = true;
}
#Override
public void fling(int startX, int startY, int velocityX, int velocityY, int minX, int maxX, int minY, int maxY) {
super.fling(startX, startY, velocityX, velocityY, minX, maxX, minY, maxY);
mIsStarted = true;
}
public void setOnFinishListener(OnFinishListener onFinishListener) {
mOnFinishListener = onFinishListener;
}
public static interface OnFinishListener {
void onFinish();
}
}