Android--view/viewgroup's "Life cycle"

The method invocation process in Title view and ViewGroup is summarized as follows:

1. First, the Activity oncreate and initializes the view

2. Then, after the Activity Onresume calls the view's Onattachedtowindow, it often does the initialization work in the Onattachedtowindow method, such as registering some broadcasts, starting the animation, etc...

3. Next, if the background is set, call OnDraw, and then call Dispatchdraw if it is viewgroup.

Description: Dispatchdraw () is mostly distributed to sub-assemblies for drawing, and we typically override the OnDraw () method when customizing components. It is noteworthy that the ViewGroup container component is drawn, and when it does not have a background, it calls the Dispatchdraw () method directly, bypassing the draw () method, invoking the draw () method when it has a background, and draw () The method contains a call to the Dispatchdraw () method. so the Dispatchdraw () method, rather than the OnDraw () method, is often overridden to draw something on ViewGroup , or a drawable is customized, the draw (Canvas C) is rewritten, and Getintrinsicwidth (), Getintrinsicheight () method, and then set as background.

4. Finally, when you click the fallback button, Activity OnDestroy after the call Ondetachedfromwindow, then we do some finishing work in this method, such as: Cancel broadcast registration, stop animation and so on.

Description: OnDraw and Dispatchdraw will probably be called multiple times due to setvisible or onresume, Onattachedtowindow and Ondetachedfromwindow are called only once during the creation and destruction of the view.

5. Onmeasure and OnLayout are also called multiple times during creation.

The following is a description of the log details, interested children to write their own demo

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Setting the background in the ViewGroup property

ViewGroup no background, viewgroup only calls Dispatchdraw and does not call OnDraw.

Onmeasure and OnLayout

Android--view/viewgroup's "Life cycle"