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Snap-to-Center RecyclerView Extension
// From: http://stackoverflow.com/a/37816976
public class SnappyRecyclerView extends RecyclerView {
// Use it with a horizontal LinearLayoutManager
// Based on http://stackoverflow.com/a/29171652/4034572
public SnappyRecyclerView(Context context) {
super(context);
}
public SnappyRecyclerView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}
public SnappyRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
// Returns the currently snapped item position
public int getFirstVisibleItemPosition() {
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) getLayoutManager();
return linearLayoutManager.findFirstCompletelyVisibleItemPosition();
}
@Override
public boolean fling(int velocityX, int velocityY) {
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) getLayoutManager();
int screenWidth = Resources.getSystem().getDisplayMetrics().widthPixels;
// views on the screen
int lastVisibleItemPosition = linearLayoutManager.findLastVisibleItemPosition();
View lastView = linearLayoutManager.findViewByPosition(lastVisibleItemPosition);
int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition();
View firstView = linearLayoutManager.findViewByPosition(firstVisibleItemPosition);
// distance we need to scroll
int leftMargin = (screenWidth - lastView.getWidth()) / 2;
int rightMargin = (screenWidth - firstView.getWidth()) / 2 + firstView.getWidth();
int leftEdge = lastView.getLeft();
int rightEdge = firstView.getRight();
int scrollDistanceLeft = leftEdge - leftMargin;
int scrollDistanceRight = rightMargin - rightEdge;
if (Math.abs(velocityX) < 1000) {
// The fling is slow -> stay at the current page if we are less than half through,
// or go to the next page if more than half through
if (leftEdge > screenWidth / 2) {
// go to next page
smoothScrollBy(-scrollDistanceRight, 0);
} else if (rightEdge < screenWidth / 2) {
// go to next page
smoothScrollBy(scrollDistanceLeft, 0);
} else {
// stay at current page
if (velocityX > 0) {
smoothScrollBy(-scrollDistanceRight, 0);
} else {
smoothScrollBy(scrollDistanceLeft, 0);
}
}
return true;
} else {
// The fling is fast -> go to next page
if (velocityX > 0) {
smoothScrollBy(scrollDistanceLeft, 0);
} else {
smoothScrollBy(-scrollDistanceRight, 0);
}
return true;
}
}
@Override
public void onScrollStateChanged(int state) {
super.onScrollStateChanged(state);
// If you tap on the phone while the RecyclerView is scrolling it will stop in the middle.
// This code fixes this. This code is not strictly necessary but it improves the behaviour.
if (state == SCROLL_STATE_IDLE) {
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) getLayoutManager();
int screenWidth = Resources.getSystem().getDisplayMetrics().widthPixels;
// views on the screen
int lastVisibleItemPosition = linearLayoutManager.findLastVisibleItemPosition();
View lastView = linearLayoutManager.findViewByPosition(lastVisibleItemPosition);
int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition();
View firstView = linearLayoutManager.findViewByPosition(firstVisibleItemPosition);
// distance we need to scroll
int leftMargin = (screenWidth - lastView.getWidth()) / 2;
int rightMargin = (screenWidth - firstView.getWidth()) / 2 + firstView.getWidth();
int leftEdge = lastView.getLeft();
int rightEdge = firstView.getRight();
int scrollDistanceLeft = leftEdge - leftMargin;
int scrollDistanceRight = rightMargin - rightEdge;
if (leftEdge > screenWidth / 2) {
smoothScrollBy(-scrollDistanceRight, 0);
} else if (rightEdge < screenWidth / 2) {
smoothScrollBy(scrollDistanceLeft, 0);
}
}
}
}
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