自定义控件基础 requestLayout()和invalidate()区别

1. requestLayout():
   重新布局整个ViewTree，开始调用measure()方法。
   requestLayout()是view的方法，view也可以调用该方法。

   Call this when something has changed which has invalidated the layout of this view. 
   This will schedule a layout pass of the view tree. This should not be called while the view hierarchy is currently in a layout pass.
   

2. invalidate():
   如果当前View可见，onDraw()方法将会被调用。

   Invalidate the whole view. If the view is visible, onDraw() will be called at some point in the future.
   This must be called from a UI thread. To call from a non-UI thread, call postInvalidate().
   

在写SimpleIndicator时，并不是一定不会走onMeasure()方法，在某种条件下会走该方法的。可以搜其他的源码分析文章，具体查看。源码分析