Wocould anyone please try to explain to me why

Public void addView (View child ){
Child. setDrawingCacheEnabled (true );
Child. setWillNotCacheDrawing (false );
Child. setWillNotDraw (false );
Child. buildDrawingCache ();
If (child. getDrawingCache () = null) {// TODO Make this work!
Log. w ("View", "View child's drawing cache is null ");
}
SetImageBitmap (child. getDrawingCache (); // todo make this work !!!
}
ALWAYS logs that the drawing cache is null, and sets the bitmap to null?
Do I have to actually draw the view before the cache is set?
Thanks!