Android - png resource converted to a ColorDrawable on android < 4.0

Question

According to documentation here, A png resource should be converted to a BitmapDrawable. However I'm observing a strange behavior wherein a png file which has only black pixels in it is resulting in a crash because of ClassCastException (wrapped in InvocationTargetException) if I try to do the following in a Custom View's constructor :

  ...
  tempDrawable = typedArr.getDrawable(R.styleable.CustomView_src); // Source points to a png file
  Log.i("TestPNGToResource", "Canonical Class Name " + tempDrawable.getClass().getCanonicalName());
  tempBitmap = ((BitmapDrawable) tempDrawable).getBitmap();
  ...

I see the following logged on android 2.2 and 2.3

09-24 13:21:37.575: I/TestPNGToResource(532): Canonical Class Name android.graphics.drawable.ColorDrawable

Why is the resource not being converted to a BitmapDrawable?

Answer 1

This is an optimization performed by aapt. It is able to recognize images made of a single color and turn them into, well, a single color instead of a bitmap. This is more space-efficient, improves loading times, etc.