animateLayoutChanges=“true” in BottomSheetView showing unexpected behaviour

Question

I have a BottomSheetView which has animateLayoutChanges=\"true\". Initially it shows up fine. But if change the visibility of a view (insi

Answer 1

The question was asked more than two years ago, but unfortunately the problem persists.

I finally got a solution to keep the call to the addView and removeView functions in a BottomSheet, while having animateLayoutChanges="true".

BottomSheetBehavior cannot calculate the correct height when it changes, so the height must remain the same. To do this, I set the height of the BottomSheet to match_parent and divide it into two children: the content and a Space that changes height according to the height of the content.

To best mimic the true behavior of a BottomSheet, you also need to add a TouchToDismiss view that darkens the background when the BottomSheet is extended but also to close the BottomSheet when the user presses outside the content.

Here's the code:

activity.xml

activity.java

BottomSheetBehavior bottomSheetBehavior;
View touchToDismiss;
LinearLayout bottomSheet;
Button showBottomSheet;
Space space;
LinearLayout bottomSheetContent;
Button addOrRemoveAnotherView;
TextView anotherView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    touchToDismiss = findViewById(R.id.touch_to_dismiss);
    touchToDismiss.setVisibility(View.GONE);
    touchToDismiss.setOnClickListener(this);

    bottomSheet = findViewById(R.id.bottom_sheet);

    bottomSheetBehavior = BottomSheetBehavior.from(bottomSheet);
    bottomSheetBehavior.setPeekHeight(0);
    bottomSheetBehavior.setState(BottomSheetBehavior.STATE_HIDDEN);
    bottomSheetBehavior.setBottomSheetCallback(new BottomSheetBehavior.BottomSheetCallback() {
        @Override
        public void onStateChanged(@NonNull View bottomSheet, int newState) {
            if (newState == BottomSheetBehavior.STATE_HIDDEN || newState == BottomSheetBehavior.STATE_COLLAPSED) {
                touchToDismiss.setVisibility(View.GONE);
            }else {
                touchToDismiss.setVisibility(View.VISIBLE);
            }
        }

        @Override
        public void onSlide(@NonNull View bottomSheet, float slideOffset) {
            touchToDismiss.setAlpha(getRealOffset());
        }
    });

    showBottomSheet = findViewById(R.id.show_bottom_sheet);
    showBottomSheet.setOnClickListener(this);

    space = findViewById(R.id.space);

    bottomSheetContent = findViewById(R.id.bottom_sheet_content);

    addOrRemoveAnotherView = findViewById(R.id.add_or_remove_another_view);
    addOrRemoveAnotherView.setOnClickListener(this);

    anotherView = findViewById(R.id.another_view);
    bottomSheetContent.removeView(anotherView);
}

@Override
public void onClick(View v) {
    if (v == showBottomSheet)
        bottomSheetBehavior.setState(BottomSheetBehavior.STATE_EXPANDED);
    else if (v == addOrRemoveAnotherView) {
        if (anotherView.getParent() == null)
            bottomSheetContent.addView(anotherView);
        else
            bottomSheetContent.removeView(anotherView);
    }
    else if (v == touchToDismiss)
        bottomSheetBehavior.setState(BottomSheetBehavior.STATE_COLLAPSED);
}

/**
 * Since the height does not change and remains at match_parent, it is required to calculate the true offset.
 * @return Real offset of the BottomSheet content.
 */
public float getRealOffset() {
    float num = (space.getHeight() + bottomSheetContent.getHeight()) - (bottomSheet.getY() + space.getHeight());

    float den = bottomSheetContent.getHeight();

    return (num / den);
}

This is the result obtained with this code:

Hopefully it will be useful to someone since the problem is still there!