Android Bottom Sheet after state changed

Question

I have an screen with a bottomsheet, but for the transition animation to work between activites I need the bottomsheet to be collapsed when the user goes on back pressed. I tried this

@Override
public void onBackPressed(){
    if (mBottomSheetBehavior.getState() == BottomSheetBehavior.STATE_COLLAPSED) {
        super.onBackPressed();
    } else {
        mBottomSheetBehavior.setState(BottomSheetBehavior.STATE_COLLAPSED);
        super.onBackPressed();
    }

    mShowingBack = false;
}

However that doesnt work as the activity goes back while the bottomsheet is only half way down.

Answer 1

BottomSheetBehavior.STATE_COLLAPSED doesn't hide all the BottomSheet, it just sets the height of the view to whatever you set with setPeekHeight() or behavior_peekHeight in the xml :) but putting that aside... you should call super.onBackPressed() inside a BottomSheetBehaviorCallback when the state of the BottomSheet is STATE_COLLAPSED, like this:

BottomSheetBehavior behavior = BottomSheetBehavior.from(mBottomSheetBehavior);  
behavior.addBottomSheetCallback(new BottomSheetCallback() {  
   @Override  
   public void onStateChanged(@NonNull View bottomSheet, int newState) {  
     if (newState == BottomSheetBehavior.STATE_COLLAPSED && mIsCollapsedFromBackPress){
        mIsCollapsedFromBackPress = false;
        super.onBackPressed();
     }
   }  

  @Override  
  public void onSlide(@NonNull View bottomSheet, float slideOffset) {  
     // React to dragging events  
  }  
});

and your backPressed() method should look like this:

@Override
public void onBackPressed(){
    mIsCollapsedFromBackPress = true;
    mBottomSheetBehavior.setState(BottomSheetBehavior.STATE_COLLAPSED);
}

Answer 2

behavior.setBottomSheetCallback(); 

Is now deprecated. Use this one instead.

BottomSheetBehavior.from(nearbyBottomSheet).addBottomSheetCallback(object :BottomSheetBehavior.BottomSheetCallback() {
        override fun onStateChanged(bottomSheet: View, newState: Int) {

        }

        override fun onSlide(bottomSheet: View, slideOffset: Float) {
                
        }
})