bottomSheetDialogFragment full screen

In your custom BottomSheetDialogFragment you can use something like:

  @NonNull @Override public Dialog onCreateDialog(Bundle savedInstanceState) {
    Dialog dialog = super.onCreateDialog(savedInstanceState);
    dialog.setOnShowListener(new DialogInterface.OnShowListener() {
      @Override public void onShow(DialogInterface dialogInterface) {
        BottomSheetDialog bottomSheetDialog = (BottomSheetDialog) dialogInterface;
        setupFullHeight(bottomSheetDialog);
      }
    });
    return  dialog;
  }


  private void setupFullHeight(BottomSheetDialog bottomSheetDialog) {
    FrameLayout bottomSheet = (FrameLayout) bottomSheetDialog.findViewById(R.id.design_bottom_sheet);
    BottomSheetBehavior behavior = BottomSheetBehavior.from(bottomSheet);
    ViewGroup.LayoutParams layoutParams = bottomSheet.getLayoutParams();

    int windowHeight = getWindowHeight();
    if (layoutParams != null) {
      layoutParams.height = windowHeight;
    }
    bottomSheet.setLayoutParams(layoutParams);
    behavior.setState(BottomSheetBehavior.STATE_EXPANDED);
  }

  private int getWindowHeight() {
    // Calculate window height for fullscreen use
    DisplayMetrics displayMetrics = new DisplayMetrics();
    ((Activity) getContext()).getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
    return displayMetrics.heightPixels;
  }

Sorry for the late answer but in your custom BottomSheetDialogFragment you can set match_parent to layout params of bottom sheet view like this:

override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    val dialog = BottomSheetDialog(requireContext(), theme)
    dialog.setOnShowListener {

        val bottomSheetDialog = it as BottomSheetDialog
        val parentLayout =
            bottomSheetDialog.findViewById<View>(com.google.android.material.R.id.design_bottom_sheet)
        parentLayout?.let { it ->
            val behaviour = BottomSheetBehavior.from(it)
            setupFullHeight(it)
            behaviour.state = BottomSheetBehavior.STATE_EXPANDED
        }
    }
    return dialog
}

private fun setupFullHeight(bottomSheet: View) {
    val layoutParams = bottomSheet.layoutParams
    layoutParams.height = WindowManager.LayoutParams.MATCH_PARENT
    bottomSheet.layoutParams = layoutParams
}

Setting height to match_parent helps your dialog to be drawn above the inset of Navigation bar

You can do it by setting peekHeight of BottomSheetBehavior to be equal to Resources.getSystem().getDisplayMetrics().heightPixels:

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    BottomSheetDialog bottomSheetDialog=(BottomSheetDialog)super.onCreateDialog(savedInstanceState);
    bottomSheetDialog.setOnShowListener(dialog -> {
        BottomSheetDialog dialogc = (BottomSheetDialog) dialog;
        // When using AndroidX the resource can be found at com.google.android.material.R.id.design_bottom_sheet
        FrameLayout bottomSheet =  dialogc.findViewById(android.support.design.R.id.design_bottom_sheet);

        BottomSheetBehavior bottomSheetBehavior = BottomSheetBehavior.from(bottomSheet);
        bottomSheetBehavior.setPeekHeight(Resources.getSystem().getDisplayMetrics().heightPixels);
        bottomSheetBehavior.setState(BottomSheetBehavior.STATE_EXPANDED);
    });
    return bottomSheetDialog;
}

Proposed solutions are based on using an internal id, since it is not on purpose exposed it could change without warning.

My solution set the layout height to the FrameLayout but in a more abstract way, so if it changes it shouldn't break, even if the ViewGroup type change.

override fun onStart() {
    super.onStart()
    val sheetContainer = requireView().parent as? ViewGroup ?: return
    sheetContainer.layoutParams.height = ViewGroup.LayoutParams.MATCH_PARENT
}

If you take a look at the BottomSheetDialog the private View wrapInBottomSheet method you will see this happens to guarantee the sheet behavior. Some extra debugging, allowed me to figure the fragment View is the direct child from the FrameLayout everybody is finding by id.

In this way, you don't need to rely on the ID. I'm using onStart because is defined at the point when the fragment is ready for interactions, so all should be ready.

And if you need it full height from the start (most probably)

override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    return BottomSheetDialog(requireContext(), theme).apply {
        behavior.state = BottomSheetBehavior.STATE_EXPANDED
        behavior.peekHeight = //your harcoded or dimen height
    }
}