code: public final void setDialogBackground(@Nullable final Bitmap background) {
          this.dialogBackground = new BitmapDrawable(getContext().getResources(), background);
          this.dialogBackgroundBitmap = background;
          this.dialogBackgroundId = -1;
          this.dialogBackgroundColor = -1;
      }
docs: Sets the background of the preference's dialog.
  
  @param background
  The background, which should be set, as an instance of the class {@link Bitmap} or
  null, if no custom background should be set