activity的启动过程 (ActivityThread, Activity, window, WindowManager, ViewRootImp)

之前只知道activity的生命周期, 不懂start, resume等在什么时候调用的, 还有第一次layout是什么时候.. 于是有了下面的记录:

一切从ActivityThread开始, ActivityThread 中的private Activity performLaunchActivity (ActivityClientRecord r,Intent customIntent) 启动一个activity.

ActivityThread里有 final ArrayMap mActivities = new ArrayMap<>();

1. handleMessage

ActivityThread里handleMessage(msg), 如果message是LAUNCH_ACTIVITY, 执行:

final ActivityClientRecord r = (ActivityClientRecord) msg.obj;

ActivityClientRecord是一个结构体, 里边有window, activity, parent, paused, stopped等.

然后调用handleLaunchActivity

2. handleLaunchActivity

先调用 WindowManagerGlobal.initialize()

然后调用performLaunchActivity, 见3

然后调用handleResumeActivity, 见4

3. performLaunchActivity

这里private Activity performLaunchActivity里, 根据已有参数, new一个activity, 然后调用:

Context appContext = createBaseContextForActivity(r,activity); 初始化context, 见3.0

activity.attach(appContext, ... ) 见 3.1

activity.performStart() 

3.0. createBaseContextForActivity

ContextImpl appContext =ContextImpl.createActivityContext(this, r.packageInfo,displayId, r.overrideConfig);

相当于new 一个ContextImpl. 

3.1 Activity.attach()

attachBaseContext(context): 

先生成mWindow, mWindow = new PhoneWindow();

mWindow.setCallback(this); 将mWindow中的mCallback设置为当前activity

然后调用mWindow的setWindowManager.  见3.2

mUiThread = Thread.currentThread() Thread.currentThread()  是指获取当前运行的线程对象

mMainThread= aThread;

3.2 Window.setWindowManager(WindowManager wm)

在window里面,会有一个WindowManager类型的成员叫做mWindowManager,它是在setWindowManager()里通过WindowManagerService这个binder通过远程调用来创建的一个WindowManagerImpl,而这个WindowManagerImpl内部会通过一个static的WindowManagerGlobal去做所有跟WindowManager有关的操作。 简而言之就是,activity中有个window,window中通过mGlobal来跟WMS交互。

mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);

createLocalWindowManager 就是 return一个新的new WindowManagerImpl(mDisplay,parentWindow);

4. handleResumeActivity

先调用performResumeActivity(这里主要调activity的performResume)

然后获得 window, decor,调用 decor的setvisibility, 然后Windowmanager的addView: wm.addView(decor,l); 见5

5. addView

WindowManager的addView是在WindowManagerGlobal里实现的:

new一个ViewRootImpl root; 然后最终调用: (这里的root是ViewRootImp, view是activity的decor)

mViews.add(view);

mRoots.add(root);

mParams.add(wparams);

然后:

root.setView(view) 见6

WindowsManagerGlobal里有重要的成员变量:

ArrayList mViews = new ArrayList();

ArrayList mRoots = new ArrayList();

ArrayList mParams = new ArrayList

6. setView

终于到ViewRootImp了. 

setView主要做的是: 

mAttachInfo.mRootView= view;

mView= view;

mAdded=true;

// Schedule the first layout -before- adding to the window

// manager, to make sure we do the relayout before receiving

// any other events from the system.

requestLayout();

后来requestLayout呢, 里边就是调用checkThread, 然后scheduleTraversals

7. 附:

VIew的 onWindowFocusChanged , 说明是这样的:

/**

* Called when the window containing this view gains or loses focus.  Note

* that this is separate from view focus: to receive key events, both

* your view and its window must have focus.  If a window is displayed

* on top of yours that takes input focus, then your own window will lose

* focus but the view focus will remain unchanged.

*

*@paramhasWindowFocusTrue if the window containing this view now has

*        focus, false otherwise.

*/

我猜: 所以是指的这个Window焦点变化, 而一个activity只有一个window, 它上面的任何一个view的这个方法都一样

Activity的onWindowFocusChanged:

* Called when the current {@linkWindow} of the activity gains or loses

* focus.  This is the best indicator of whether this activity is visible

* to the user.  The default implementation clears the key tracking

* state, so should always be called.

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