@Override
  public int getIntrinsicWidth() {
    int width = -1;
    for (int i = 0; i < mLayers.length; i++) {
      Drawable drawable = mLayers[i];
      if (drawable != null) {
        width = Math.max(width, drawable.getIntrinsicWidth());
      }
    }
    return width > 0 ? width : -1;
  }
Sets a new drawable at the specified index, and return the previous drawable, if any.
drawee/src/main/java/com/facebook/drawee/drawable/ArrayDrawable.java