以下是android.view的调用堆栈：

Thread [<3> main] (Suspended (breakpoint at line 12 in MyContentView))
MyContentView.onDraw(Canvas) line: 12
MyContentView(View).draw(Canvas) line: 6535
FrameLayout(ViewGroup).drawChild(Canvas, View, long) line: 1531
FrameLayout(ViewGroup).dispatchDraw(Canvas) line: 1258
FrameLayout(View).draw(Canvas) line: 6538 

如何理解FrameLayout(ViewGroup)和FrameLayout(View)？