View.AttachInfo的前世今生

View所持有的AttachInfo来自于根布局的ViewRootImpl。

同一个window下的view，持有的AttachInfo都是同一份。

1、View#AttachInfo：当view 被跟父window关联起来时，被设置给view的一系列信息。

A set of information given to a view when it is attached to its parent window.

@UnsupportedAppUsage

final IWindowSession mSession;

@UnsupportedAppUsage

final IWindow mWindow;

final IBinder mWindowToken;

Display mDisplay;

final Callbacks mRootCallbacks;

IWindowId mIWindowId;

WindowId mWindowId;

/**

* The top view of the hierarchy.

*/

View mRootView;

IBinder mPanelParentWindowToken;

boolean mHardwareAccelerated;

boolean mHardwareAccelerationRequested;

ThreadedRenderer mThreadedRenderer;

List<RenderNode> mPendingAnimatingRenderNodes;

...

2、何时、哪里生成的：ViewRootImpl

ViewRootImpl的构造函数中：

ViewRootImpl(Context context, Display display, IWindowSession session, boolean useSfChoreographer){

mAttachInfo = new View.AttachInfo(mWindowSession, mWindow, display, this, mHandler, this, context);

}

3、何时设置给View？

①activity启动时，渲染布局：

--> ViewRootImpl#doTraversal()

--> ViewRootImpl#performTraversals()

--> Decorview#dispatchAttachedToWindow(AttachInfo info, int visibility)

--> ViewGroup#dispatchAttachedToWindow(AttachInfo info, int visibility)

--> View#dispatchAttachedToWindow(AttachInfo info, int visibility): the android.view.View.AttachInfo to associated with this view

②动态添加View：比如点击button时，给root添加子View。

示例代码：

LinearLayout root = findViewById(R.id.root);

Button btn = findViewById(R.id.btn_add);

btn.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

View view = new View(DispatchAttachInfoTestActivity.this);

view.setBackgroundColor(getResources().getColor(R.color.background_info));

LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(300, 300);

root.addView(view, lp);

}

});

调用栈：

--> View.OnClickListener#onClick(View v)

--> ViewGroup#addView(View child, LayoutParams params)

--> ViewGroup#addView(View child, int index, LayoutParams params)

--> ViewGroup#addViewInner(View child, int index, LayoutParams params, boolean preventRequestLayout)

--> View#dispatchAttachedToWindow(AttachInfo info, int visibility)

总结

①View#AttachInfo由ViewRootImpl生成，mAttachInfo实例维护在ViewRootImpl中。

②最先设置给根root。

③当view树中添加新的View时，会由parent将其mAttachInfo设置给child。

最终保证了整个View数中的View#AttachInfo是同一个对象。