BottomSheetDialog with transparent background

BottomSheetDialog bottomSheetDialog =new BottomSheetDialog(this,R.style.SheetDialog);

<style name="SheetDialog" parent="Theme.Design.Light.BottomSheetDialog">
    <!--<item name="android:windowCloseOnTouchOutside">false</item>-->
    <item name="android:windowIsTranslucent">true</item>
    <item name="android:windowContentOverlay">@null</item>
    <item name="android:colorBackground">     @android:color/transparent</item>
    <item name="android:backgroundDimEnabled">true</item>
    <item name="android:backgroundDimAmount">0.3</item>
    <item name="android:windowFrame">@null</item>
    <item name="android:windowIsFloating">true</item>
</style>

This is simplest solution for set transparent background of BottomSheetDialogFragment

It makes use of the following line of code:

 ((View) contentView.getParent()).setBackgroundColor(getResources().getColor(android.R.color.transparent));

Example in context:

public class ShareOneTouchAlertNewBottom extends BottomSheetDialogFragment {
    @Override
    public void setupDialog(Dialog dialog, int style) {
        super.setupDialog(dialog, style);
        View contentView = View.inflate(getContext(), R.layout.fragment_bottom_sheet, null);
        dialog.setContentView(contentView);

        CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams) ((View) contentView.getParent())
                .getLayoutParams();
        CoordinatorLayout.Behavior behavior = params.getBehavior();
        ((View) contentView.getParent()).setBackgroundColor(Color.TRANSPARENT);
    }
}

This worked for me when using BottomSheetDialogFragment:

public class CustomDialogFragment extends BottomSheetDialogFragment {

  @Override
  public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setStyle(BottomSheetDialogFragment.STYLE_NORMAL, R.style.CustomBottomSheetDialogTheme);
  }
  
  ...
}

Also add this to your styles.xml

<style name="CustomBottomSheetDialogTheme" parent="Theme.Design.Light.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/CustomBottomSheetStyle</item>
</style>

<style name="CustomBottomSheetStyle" parent="Widget.Design.BottomSheet.Modal">
    <item name="android:background">@android:color/transparent</item>
</style>

Option 2:

override fun getTheme() = R.style.CustomBottomSheetDialogTheme