前言
很久没有发表文章了，今天来一篇，大家撒花～～～
本文打算分析下Android中点击事件的来源，顺便提及下ViewRootImpl。
Android中点击事件的来源
这个问题，也许你会说“这还用你说吗？我可是看过艺术探索的人”，我知道艺术探索中的确是详细介绍了点击事件的传递流程，反正大致就是点击事件从Activity传递给PhoneWindow，然后PhoneWindow再传递给DecorView，接着DecorView就进行后续的遍历式的传递。这都没错，但是点击事件是谁传递给Activity的呢？这个大家可能不清楚吧？那本文就是分析这个问题的。
首先看Activity的实现，如下，Activity实现了一个特殊的接口：Window.Callback。
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public class Activity extends ContextThemeWrapper implements LayoutInflater.Factory2, Window.Callback, KeyEvent.Callback, OnCreateContextMenuListener, ComponentCallbacks2, Window.OnWindowDismissedCallback { private static final String TAG = "Activity"; private static final boolean DEBUG_LIFECYCLE = false; |
那么Window.Callback到底是什么东西呢？如下：
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/** * API from a Window back to its caller. This allows the client to * intercept key dispatching, panels and menus, etc. */ public interface Callback { /** * Called to process key events. At the very least your * implementation must call * {<a href="http://www.jobbole.com/members/57845349" data-mce-href="http://www.jobbole.com/members/57845349">@link</a> android.view.Window#superDispatchKeyEvent} to do the * standard key processing. * * @param event The key event. * * @return boolean Return true if this event was consumed. */ public boolean dispatchKeyEvent(KeyEvent event); /** * Called to process touch screen events. At the very least your * implementation must call * {<a href="http://www.jobbole.com/members/57845349" data-mce-href="http://www.jobbole.com/members/57845349">@link</a> android.view.Window#superDispatchTouchEvent} to do the * standard touch screen processing. * * @param event The touch screen event. * * @return boolean Return true if this event was consumed. */ public boolean dispatchTouchEvent(MotionEvent event); /** * Called to process trackball events. At the very least your * implementation must call * {<a href="http://www.jobbole.com/members/57845349" data-mce-href="http://www.jobbole.com/members/57845349">@link</a> android.view.Window#superDispatchTrackballEvent} to do the * standard trackball processing. * * @param event The trackball event. * * @return boolean Return true if this event was consumed. */ public boolean dispatchTrackballEvent(MotionEvent event); ...（省略若干代码，下同） |
然后我们似乎看出了一些端倪，难道这个接口和点击事件的传递有关？嗯，你猜对了。在艺术探索这本书中，并没有描述事件是如何传递给Activity的，但是这里我们可以猜测，如果外界想要传递点击事件给Activity，那么它就必须持有Activity的引用，这没错，在Activity的attach方法中，有如下一段：
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final void attach(Context context, ActivityThread aThread, Instrumentation instr, IBinder token, int ident, Application application, Intent intent, ActivityInfo info, CharSequence title, Activity parent, String id, NonConfigurationInstances lastNonConfigurationInstances, Configuration config, String referrer, IVoiceInteractor voiceInteractor) { attachBaseContext(context); mFragments.attachHost(null /*parent*/); mWindow = new PhoneWindow(this); mWindow.setCallback(this); mWindow.setOnWindowDismissedCallback(this); mWindow.getLayoutInflater().setPrivateFactory(this); |
显然，mWindow持有了Activity的引用，它通过setCallback方法来持有Activity，因此，事件是从Window传递给了Activity。也许你会说：“我不信，这理由不充分！”，没关系，我们继续分析。
我们知道，Activity启动以后，在它的onResume以后，DecorView才开始attach给WindowManager从而显示出来。（什么？你不知道？回去看艺术探索第8章），请看Activity的makeVisible方法，代码如下：
