深入理解WMS（二）：Dialog与Toast源码解析

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Activity的启动过程很复杂，最终是有ActivityThread中的performLaunchActivity方法来完成的，看上图源码可以看出performLaunchActivity是通过类加载器获得Activity的实例的。然后调动Activity的attach方法为其关联运行过程中所依赖的一系列上下文环境变量。

在Activity的attach方法里，

• 系统会创建Activity所属的Window对象并为其设置回调接口，这里Window对象实际上是PhoneWindow。

• 给Activity初始化各种参数，如mUiThread等

• 给PhoneWindow设置WindowManager，实际上设置的是WindowManagerImpl：

下图给出一部分源码，有兴趣的同学还是直接看源码。

…

mWindow = new PhoneWindow(this, window, activityConfigCallback);

mWindow.setWindowControllerCallback(this);

mWindow.setCallback(this);

mWindow.setOnWindowDismissedCallback(this);

mWindow.getLayoutInflater().setPrivateFactory(this);

if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {

mWindow.setSoftInputMode(info.softInputMode);

}

if (info.uiOptions != 0) {

mWindow.setUiOptions(info.uiOptions);

}

mUiThread = Thread.currentThread();

mMainThread = aThread;

mInstrumentation = instr;

mToken = token;

mIdent = ident;

mApplication = application;

mIntent = intent;

mReferrer = referrer;

mComponent = intent.getComponent();

mActivityInfo = info;

mTitle = title;

mParent = parent;

mEmbeddedID = id;

mLastNonConfigurationInstances = lastNonConfigurationInstances;

if (voiceInteractor != null) {

if (lastNonConfigurationInstances != null) {

mVoiceInteractor = lastNonConfigurationInstances.voiceInteractor;

} else {

mVoiceInteractor = new VoiceInteractor(voiceInteractor, this, this,

Looper.myLooper());

}

}

mWindow.setWindowManager(

(WindowManager)context.getSystemService(Context.WINDOW_SERVICE),

mToken, mComponent.flattenToString(),

(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);

if (mParent != null) {

mWindow.setContainer(mParent.getWindow());

}

mWindowManager = mWindow.getWindowManager();

mCurrentConfig = config;\

mWindow.setColorMode(info.colorMode);

…

由于Activity实现了Window的Callback接口，因此当Window接收到外界的状态改变时就会回调Activity的方法。Callback接口中的方法很多，但是有几个却是我们都非常熟悉的，比如onAttachedToWindow、onDetachedFromWindow、dispatchTouchEvent，等等。

public interface Callback {

public boolean dispatchKeyEvent(KeyEvent event);

public boolean dispatchKeyShortcutEvent(KeyEvent event);

public boolean dispatchTouchEvent(MotionEvent event);

public boolean dispatchTrackballEvent(MotionEvent event);

public boolean dispatchGenericMotionEvent(MotionEvent event);

…

到这里Window已经创建完成了，但是像之前文章说过的一样，只有Window其实只是一个空的架子，还需要View才能真正是出现视图。Activity的视图是怎么加到Window中的呢？这里就得说道一个我们很熟悉的方法setContentView。

…

/**

• Set the activity content from a layout resource. The resource will be

• inflated, adding all top-level views to the activity.

• @param layoutResID Resource ID to be inflated.

• @see #setContentView(android.view.View)