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Android View系统分析之三Activity的启动与显示
前言
Activity的启动过程
我们知道,在Android系统启动时,第一个启动起来的进程就是zygote进程,然后由zygote启动SystemServer,再然后就是启动例如ActivityManagerService、WindowManagerService等系统核心服务,这些服务承载着整个Android系统与客户端程序交互的重担。zygote除了启动系统服务与进程之外,普通的用户进程也由zygote进程fork而来,当一个应用进程启动起来后,就会加载用户在AndroidManifest.xml中配置的默认加载的Activity。此时加载的入口是ActivityThread.main(String[] args)方法,这个方法就是类似于C语言中的main方法一样,是整个应用程序的入口。
在ActivityThread.main(String[] args)这个方法中,主要的功能就是创建Application和创建Activity,并且调用Activity的一些生命周期函数,例如onCreate、onResume等。下面我们就从ActivityThread.main(String[] args)这个入口开始学习吧。
public static final void main(String[] args) { SamplingProfilerIntegration.start(); Process.setArgV0("<pre-initialized>"); // 1、创建UI线程的Looper Looper.prepareMainLooper(); if (sMainThreadHandler == null) { sMainThreadHandler = new Handler(); } // 2、创建ActivityThread对象,但它并不是线程感觉是封装了UI线程消息循环与操作Activity生命周期的工具类 ActivityThread thread = new ActivityThread(); // 3、调用ActivityThread的attach方法,这是核心方法,Application、Activity的创建入口就在这里 thread.attach(false); if (false) { Looper.myLooper().setMessageLogging(new LogPrinter(Log.DEBUG, "ActivityThread")); } // 4、启动UI线程消息循环 Looper.loop(); if (Process.supportsProcesses()) { throw new RuntimeException("Main thread loop unexpectedly exited"); } thread.detach(); String name = (thread.mInitialApplication != null) ? thread.mInitialApplication.getPackageName() : "<unknown>"; Slog.i(TAG, "Main thread of " + name + " is now exiting"); } // UI线程与Application关联 private final void attach(boolean system) { sThreadLocal.set(this); mSystemThread = system; // 不是系统进程 if (!system) { ViewRoot.addFirstDrawHandler(new Runnable() { public void run() { ensureJitEnabled(); } }); android.ddm.DdmHandleAppName.setAppName("<pre-initialized>"); RuntimeInit.setApplicationObject(mAppActivityManagerNativeThread.asBinder()); // 5、获取ActivityManagerService实例 IActivityManager mgr = ActivityManagerNative.getDefault(); try { // 6、注意这里,将mAppThread与Application进行管理 mgr.attachApplication(mAppThread); } catch (RemoteException ex) { } } else { // 代码省略 } // 代码省略 }可以看到,在ActivityThread.main中主要的功能就是创建了UI线程消息循环,并且启动了消息循环。最重要的是创建了ActivityThread,并调用了attach方法。在attach方法中又调用了ActivityManagerService中的attachApplication(mAppThread)方法,这个才是我们的重点。mAppThread是ApplicationThread类型,它也不是一个Thread,而是一个Binder,负责与远程的ActivityManagerService进行交互。在了解attachApplication之前,我们先来了解一下ApplicationThread与ActivityThread的关联。代码如下 :
public final class ActivityThread { // 定义mAppThread与mH final ApplicationThread mAppThread = new ApplicationThread(); final Looper mLooper = Looper.myLooper(); final H mH = new H(); // if the thread hasn‘t started yet, we don‘t have the handler, so just // save the messages until we‘re ready. private final void queueOrSendMessage(int what, Object obj) { queueOrSendMessage(what, obj, 0, 0); } private final void queueOrSendMessage(int what, Object obj, int arg1) { queueOrSendMessage(what, obj, arg1, 0); } private final void queueOrSendMessage(int what, Object obj, int arg1, int arg2) { synchronized (this) { if (DEBUG_MESSAGES) Slog.v( TAG, "SCHEDULE " + what + " " + mH.codeToString(what) + ": " + arg1 + " / " + obj); Message msg = Message.obtain(); msg.what = what; msg.obj = obj; msg.arg1 = arg1; msg.arg2 = arg2; // 通过mH来发消息, 处理也在H类中的handleMessage函数中 mH.sendMessage(msg); } } /// AppcationThread 内部类,负责与ActivityManagerService交互 private final class ApplicationThread extends ApplicationThreadNative { private static final String HEAP_COLUMN = "%17s %8s %8s %8s %8s"; private static final String ONE_COUNT_COLUMN = "%17s %8d"; private static final String TWO_COUNT_COLUMNS = "%17s %8d %17s %8d"; private static final String TWO_COUNT_COLUMNS_DB = "%20s %8d %20s %8d"; private static final String DB_INFO_FORMAT = " %8d %8d %14d %s"; // Formatting for checkin service - update version if row format changes private static final int ACTIVITY_THREAD_CHECKIN_VERSION = 1; // 向UI线程发一个resume activity的消息 public final void scheduleResumeActivity(IBinder token, boolean isForward) { queueOrSendMessage(H.RESUME_ACTIVITY, token, isForward ? 1 : 0); } // we use token to identify this activity without having to send the // activity itself back to the activity manager. (matters more with ipc) public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident, ActivityInfo info, Bundle state, List<ResultInfo> pendingResults, List<Intent> pendingNewIntents, boolean notResumed, boolean isForward) { ActivityClientRecord r = new ActivityClientRecord(); r.token = token; r.ident = ident; r.intent = intent; r.activityInfo = info; r.state = state; r.pendingResults = pendingResults; r.pendingIntents = pendingNewIntents; r.startsNotResumed = notResumed; r.isForward = isForward; // 向UI线程发一个H.LAUNCH_ACTIVITY的消息 queueOrSendMessage(H.LAUNCH_ACTIVITY, r); } // 省略代码 } // end ApplicationThread // H内部类, ApplicationThread通过H类型的对象向UI线程投递消息 private final class H extends Handler { public static final int LAUNCH_ACTIVITY = 100; public static final int PAUSE_ACTIVITY = 101; public static final int PAUSE_ACTIVITY_FINISHING= 102; // 其他code省略 String codeToString(int code) { if (DEBUG_MESSAGES) { switch (code) { case LAUNCH_ACTIVITY: return "LAUNCH_ACTIVITY"; case PAUSE_ACTIVITY: return "PAUSE_ACTIVITY"; case PAUSE_ACTIVITY_FINISHING: return "PAUSE_ACTIVITY_FINISHING"; // 代码省略 } } return "(unknown)"; } public void handleMessage(Message msg) { if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + msg.what); switch (msg.what) { case LAUNCH_ACTIVITY: { ActivityClientRecord r = (ActivityClientRecord)msg.obj; r.packageInfo = getPackageInfoNoCheck( r.activityInfo.applicationInfo); // 加载Activity handleLaunchActivity(r, null); } break; // activity pause case PAUSE_ACTIVITY: handlePauseActivity((IBinder)msg.obj, false, msg.arg1 != 0, msg.arg2); maybeSnapshot(); break; // 代码省略 } if (DEBUG_MESSAGES) Slog.v(TAG, "<<< done: " + msg.what); } } // end H } // end ActivityThreadApplicationThread与ActivityManagerService进行交互,然后通过H类的对象mH来发送消息,并且在H类的handleMessage函数中进行处理,然后handleMessage根据消息的类型调用ActivityThread中对应的方法,比如handleResumeActivity来使Activity变得可见等。因为H的消息队列就是主线程的消息队列,因此这些过程都在UI线程中处理。
好的,我们现在继续关注ActivityManagerService中的attachApplication( mAppThread )。
public final void attachApplication(IApplicationThread thread) { synchronized (this) { int callingPid = Binder.getCallingPid(); final long origId = Binder.clearCallingIdentity(); // 1、转到了attachApplicationLocked attachApplicationLocked(thread, callingPid); Binder.restoreCallingIdentity(origId); } } private final boolean attachApplicationLocked(IApplicationThread thread, int pid) { // 代码省略 if (localLOGV) Slog.v( TAG, "New app record " + app + " thread=" + thread.asBinder() + " pid=" + pid); try { // 2、ApplicationThread绑定Application thread.bindApplication(processName, app.instrumentationInfo != null ? app.instrumentationInfo : app.info, providers, app.instrumentationClass, app.instrumentationProfileFile, app.instrumentationArguments, app.instrumentationWatcher, testMode, isRestrictedBackupMode || !normalMode, mConfiguration, getCommonServicesLocked()); updateLruProcessLocked(app, false, true); app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis(); } catch (Exception e) { return false; } // 代码省略 // See if the top visible activity is waiting to run in this process... ActivityRecord hr = mMainStack.topRunningActivityLocked(null); if (hr != null && normalMode) { if (hr.app == null && app.info.uid == hr.info.applicationInfo.uid && processName.equals(hr.processName)) { try { // 3、正确启动Activity if (mMainStack.realStartActivityLocked(hr, app, true, true)) { didSomething = true; } } catch (Exception e) { Slog.w(TAG, "Exception in new application when starting activity " + hr.intent.getComponent().flattenToShortString(), e); badApp = true; } } else { mMainStack.ensureActivitiesVisibleLocked(hr, null, processName, 0); } } return true; }在省略了一大波代码之后,我们抓住了我们需要关心的点,即注释3处,这里才是真正启动activity的地方,这名字真是起得实诚。mMainStack的类型为ActivityStack,我们看看realStartActivityLocked吧。
// 3中的ActivityStack中的realStartActivityLocked方法 final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app, boolean andResume, boolean checkConfig) throws RemoteException { // 代码省略 try { // 代码省略 // 设置app的dex文件的所在位置,指定包名 mService.ensurePackageDexOpt(r.intent.getComponent().getPackageName()); // 1、注意这里调用了ApplicationThread中的scheduleLaunchActivity方法, 这个方法中会给UI线程发一个 // LAUNCH_ACTIVITY消息,然后会调用ActivityThread的handleLaunchActivity(ActivityClientRecord r, Intent customIntent)函数 // 在这个函数中会创建Activity,并且调用Activity的onCreate、onResume函数 app.thread.scheduleLaunchActivity(new Intent(r.intent), r, System.identityHashCode(r), r.info, r.icicle, results, newIntents, !andResume, mService.isNextTransitionForward()); // 代码省略 } catch (RemoteException e) { } // 代码省略 return true; }好嘛,绕来绕去,最终调用了ActiivityThread中的内部类的ApplicationThread中的scheduleLaunchActivity函数。该函数会发一个这个方法中会给UI线程发一个
H.LAUNCH_ACTIVITY消息,然后会调用ActivityThread的handleLaunchActivity(ActivityClientRecord r, Intent customIntent)函数,在这个函数中会创建将要启动的Activity,并且调用其生命周期函数onCreate、onResume,至此,Activity就启动,并且显示在我们的设备上了。
// ActivityThread中的handleLaunchActivity private final void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) { // If we are getting ready to gc after going to the background, well // we are back active so skip it. unscheduleGcIdler(); if (localLOGV) Slog.v( TAG, "Handling launch of " + r); // 1、创建并且加载Activity,调用其onCreate函数 Activity a = performLaunchActivity(r, customIntent); if (a != null) { r.createdConfig = new Configuration(mConfiguration); Bundle oldState = r.state; // 2、调用Activity的onResume方法,使Activity变得可见 handleResumeActivity(r.token, false, r.isForward); } } private final Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) { // System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")"); ActivityInfo aInfo = r.activityInfo; if (r.packageInfo == null) { r.packageInfo = getPackageInfo(aInfo.applicationInfo, Context.CONTEXT_INCLUDE_CODE); } ComponentName component = r.intent.getComponent(); if (component == null) { component = r.intent.resolveActivity( mInitialApplication.getPackageManager()); r.intent.setComponent(component); } if (r.activityInfo.targetActivity != null) { component = new ComponentName(r.activityInfo.packageName, r.activityInfo.targetActivity); } Activity activity = null; try { java.lang.ClassLoader cl = r.packageInfo.getClassLoader(); // 1、创建Activity activity = mInstrumentation.newActivity( cl, component.getClassName(), r.intent); r.intent.setExtrasClassLoader(cl); if (r.state != null) { r.state.setClassLoader(cl); } } catch (Exception e) { if (!mInstrumentation.onException(activity, e)) { throw new RuntimeException( "Unable to instantiate activity " + component + ": " + e.toString(), e); } } try { // 2、创建Application Application app = r.packageInfo.makeApplication(false, mInstrumentation); if (localLOGV) Slog.v(TAG, "Performing launch of " + r); if (localLOGV) Slog.v( TAG, r + ": app=" + app + ", appName=" + app.getPackageName() + ", pkg=" + r.packageInfo.getPackageName() + ", comp=" + r.intent.getComponent().toShortString() + ", dir=" + r.packageInfo.getAppDir()); if (activity != null) { // 构建Context ContextImpl appContext = new ContextImpl(); appContext.init(r.packageInfo, r.token, this); appContext.setOuterContext(activity); // 获取Activity的title CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager()); Configuration config = new Configuration(mConfiguration); // 3、Activity与context, Application关联起来 activity.attach(appContext, this, getInstrumentation(), r.token, r.ident, app, r.intent, r.activityInfo, title, r.parent, r.embeddedID, r.lastNonConfigurationInstance, r.lastNonConfigurationChildInstances, config); if (customIntent != null) { activity.mIntent = customIntent; } r.lastNonConfigurationInstance = null; r.lastNonConfigurationChildInstances = null; activity.mStartedActivity = false; int theme = r.activityInfo.getThemeResource(); if (theme != 0) { activity.setTheme(theme); } activity.mCalled = false; // 4、回调Activity的onCreate方法 mInstrumentation.callActivityOnCreate(activity, r.state); if (!activity.mCalled) { throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onCreate()"); } r.activity = activity; r.stopped = true; // 5、执行Activity的onStart方法 if (!r.activity.mFinished) { activity.performStart(); r.stopped = false; } // 代码省略 } r.paused = true; mActivities.put(r.token, r); } catch (SuperNotCalledException e) { throw e; } catch (Exception e) { } return activity; } final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward) { // If we are getting ready to gc after going to the background, well // we are back active so skip it. unscheduleGcIdler(); // 1、最终调用Activity的onResume方法 ActivityClientRecord r = performResumeActivity(token, clearHide); if (r != null) { final Activity a = r.activity; final int forwardBit = isForward ? WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0; // If the window hasn‘t yet been added to the window manager, // and this guy didn‘t finish itself or start another activity, // then go ahead and add the window. boolean willBeVisible = !a.mStartedActivity; if (!willBeVisible) { try { willBeVisible = ActivityManagerNative.getDefault().willActivityBeVisible( a.getActivityToken()); } catch (RemoteException e) { } } // 2、这里是重点,在这里使DecorView变得可见 if (r.window == null && !a.mFinished && willBeVisible) { // 获取Window,即PhoneWindow类型 r.window = r.activity.getWindow(); // 3、获取Window的顶级视图,并且使它可见 View decor = r.window.getDecorView(); decor.setVisibility(View.INVISIBLE); // 4、获取WindowManager ViewManager wm = a.getWindowManager(); // 5、构建LayoutParams参数 WindowManager.LayoutParams l = r.window.getAttributes(); a.mDecor = decor; l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION; l.softInputMode |= forwardBit; if (a.mVisibleFromClient) { a.mWindowAdded = true; // 6、将DecorView添加到WindowManager中,最终的操作是通过WindowManagerService的addView来操作 wm.addView(decor, l); } // If the window has already been added, but during resume // we started another activity, then don‘t yet make the // window visible. } else if (!willBeVisible) { if (localLOGV) Slog.v( TAG, "Launch " + r + " mStartedActivity set"); r.hideForNow = true; } // 代码省略 } // public final ActivityClientRecord performResumeActivity(IBinder token, boolean clearHide) { ActivityClientRecord r = mActivities.get(token); if (r != null && !r.activity.mFinished) { try { // 代码省略 // 执行onResume r.activity.performResume(); r.paused = false; r.stopped = false; r.state = null; } catch (Exception e) { } } return r; }
如上述代码,在调用ActivityThread的handleLaunchActivity(ActivityClientRecord r, Intent customIntent)后会调用performLaunchActivity函数来创建Activity,并且将Activity与Application关联上,然后调用Activity的onCreate、onStart函数。再之后是调用handleResumeActivity函数,handleResumeActivity函数又调用performResumeActivity函数来回调Activity的onResume函数,之后将Activity的DecorView设置为可见,并且添加到WindowManager中,此时Activity也就显示在屏幕上了。
由此,我们可以得出,在Activity的onResume方法中,Activity的内容还是没有可见,执行完OnResume之后才会可见。那么Activity的DecorView又是如何通过WindowManager显示在屏幕上的呢?我们下篇文章再来学习吧~
Android View系统分析之三Activity的启动与显示