四.Activity的启动流程-ActivityThread启动Activity的过程

Activity的启动一般分为普通Activity的启动,根Activity的启动.而根Activity是指应用启动的第一个Activity过程,所以也可以理解为应用的启动过程.

相关内容链接：android系统启动流程

应用的启动流程大致分为如下四个阶段:

一.应用进程(Launcher)调用ATMS系统进程的过程

二.ActivityTaskManagerService到ApplicationThread的调用过程

三.AMS向Zygote发送启动应用进程的过程

四.ActivityThread启动Activity的过程

Activity启动过程涉及到进程之间的关系:

四.ActivityThread启动Activity的过程

类名: android.app.ActivityThread.ApplicationThread

ApplicationThread类可以看作是AMS所在进程(SystemServer进程)和应用进程通信的桥梁,通过Binder的方式来执行

ActivityThread主要用来处理Activity生命周期等一些逻辑,ActivityThread继承自抽象类ClientTransactionHandler,将以前ActivityThread里面的handleLaunchActivity、handleStartActivity、handleResumeActivity和handleStopActivity等方法抽取出来,作为ClientTransactionHandler类的抽象方法.

1. scheduleTransaction

ApplicationThread继承自IApplicationThread.Stub,第二阶段中IApplicationThread的Binder调用就会执行到这里,这块代码比较简单,调用ActivityThread的scheduleTransaction方法,而ActivityThread是继承自抽象类ClientTransactionHandler, ActivityThread没有重写该方法,所以这里就会调用到ClientTransactionHandler的scheduleTransaction方法.

    @Overridepublic void scheduleTransaction(ClientTransaction transaction) throws RemoteException {ActivityThread.this.scheduleTransaction(transaction);}

类名: android.app.ClientTransactionHandler:

2. scheduleTransaction

    void scheduleTransaction(ClientTransaction transaction) {transaction.preExecute(this);sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);}

类名: android.app.ActivityThread.H

3. handleMessage()

        class H extends Handler {public void handleMessage(Message msg) {// ... ...case EXECUTE_TRANSACTION:final ClientTransaction transaction = (ClientTransaction) msg.obj;mTransactionExecutor.execute(transaction);if (isSystem()) {// Client transactions inside system process are recycled on the client side// instead of ClientLifecycleManager to avoid being cleared before this// message is handled.transaction.recycle();}// TODO(lifecycler): Recycle locally scheduled transactions.break;// ... ...}}

类名: android.app.servertransaction.TransactionExecutor

4: execute(ClientTransaction)

这里的executeCallbacks主要是用来实例化和初始化activity,而executeLifecycleState主要是回调Activity的声明周期方法.

 public void execute(ClientTransaction transaction) {// ... ...executeCallbacks(transaction);executeLifecycleState(transaction);mPendingActions.clear();if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "End resolving transaction");}

5. executeCallbacks()

这里callbacks列表中存放的是第二阶段(序号15.realStartActivityLocked方法)中创建事务时设置进去的,即LaunchActivityItem.所以这里是执行LaunchActivityItem对象的execute方法

 public void executeCallbacks(ClientTransaction transaction) {final List<ClientTransactionItem> callbacks = transaction.getCallbacks();// ... ...final int size = callbacks.size();for (int i = 0; i < size; ++i) {final ClientTransactionItem item = callbacks.get(i);    // LaunchActivityItem是继承自LaunchActivityItemif (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "Resolving callback: " + item);final int postExecutionState = item.getPostExecutionState();final int closestPreExecutionState = mHelper.getClosestPreExecutionState(r,item.getPostExecutionState());if (closestPreExecutionState != UNDEFINED) {cycleToPath(r, closestPreExecutionState, transaction);}item.execute(mTransactionHandler, token, mPendingActions);item.postExecute(mTransactionHandler, token, mPendingActions);if (r == null) {// Launch activity request will create an activity record.r = mTransactionHandler.getActivityClient(token);}if (postExecutionState != UNDEFINED && r != null) {// Skip the very last transition and perform it by explicit state request instead.final boolean shouldExcludeLastTransition =i == lastCallbackRequestingState && finalState == postExecutionState;cycleToPath(r, postExecutionState, shouldExcludeLastTransition, transaction);}}}

类名: android.app.servertransaction.LaunchActivityItem

6. execute(ClientTransactionHandler, IBinder, PendingTransactionActions)

类名: android.app.ActivityThread

7. handleLaunchActivity(ActivityClientRecord , PendingTransactionActions, Intent)

类名: android.app.ActivityThread

8. performLaunchActivity()

这里主要是获取当前Activity的信息,创建Activity的上下文和实例,创建Application,调用Activity的attach方法初始化activity,在attach方法中会创建Window对象(PhoneWindow)并与Activity关联起来,最后调用callActivityOnCreate()方法来启动Activity.

    /**  Core implementation of activity launch. */private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {ActivityInfo aInfo = r.activityInfo;    //记录Manifest设置的Activity和Receiver节点信息,比如theme和launchModeif (r.packageInfo == null) {r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,Context.CONTEXT_INCLUDE_CODE);  //获取APK文件描述类LoadedApk}ComponentName component = r.intent.getComponent();  // 获取Activity的ComponentName(记录了包名和类名)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);}ContextImpl appContext = createBaseContextForActivity(r);   // 创建启动Activity的上下文Activity activity = null;try {java.lang.ClassLoader cl = appContext.getClassLoader();activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);    // 使用ClassLoader创建Activity实例StrictMode.incrementExpectedActivityCount(activity.getClass());r.intent.setExtrasClassLoader(cl);r.intent.prepareToEnterProcess();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 {Application app = r.packageInfo.makeApplication(false, mInstrumentation);   // 创建Applicationif (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) {CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());Configuration config = new Configuration(mCompatConfiguration);if (r.overrideConfig != null) {config.updateFrom(r.overrideConfig);}if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "+ r.activityInfo.name + " with config " + config);Window window = null;if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {window = r.mPendingRemoveWindow;r.mPendingRemoveWindow = null;r.mPendingRemoveWindowManager = null;}appContext.setOuterContext(activity);activity.attach(appContext, this, getInstrumentation(), r.token,r.ident, app, r.intent, r.activityInfo, title, r.parent,r.embeddedID, r.lastNonConfigurationInstances, config,r.referrer, r.voiceInteractor, window, r.configCallback,r.assistToken); // 初始化Activityif (customIntent != null) {activity.mIntent = customIntent;}r.lastNonConfigurationInstances = null;checkAndBlockForNetworkAccess();activity.mStartedActivity = false;int theme = r.activityInfo.getThemeResource();if (theme != 0) {activity.setTheme(theme);}activity.mCalled = false;if (r.isPersistable()) {mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);} else {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.setState(ON_CREATE);// updatePendingActivityConfiguration() reads from mActivities to update// ActivityClientRecord which runs in a different thread. Protect modifications to// mActivities to avoid race.synchronized (mResourcesManager) {mActivities.put(r.token, r);}} catch (SuperNotCalledException e) {throw e;} catch (Exception e) {if (!mInstrumentation.onException(activity, e)) {throw new RuntimeException("Unable to start activity " + component+ ": " + e.toString(), e);}}return activity;}

类名: android.app.Instrumentation

9. callActivityOnCreate(Activity, Bundle, PersistableBundle)

类名: android.app.Activity

10. performCreate(Bundle)()

performCreate中会调用Activity的onCreate.Activity的启动就完成了,应用也就启动了.

    @UnsupportedAppUsagefinal void performCreate(Bundle icicle, PersistableBundle persistentState) {dispatchActivityPreCreated(icicle);mCanEnterPictureInPicture = true;restoreHasCurrentPermissionRequest(icicle);if (persistentState != null) {onCreate(icicle, persistentState);} else {onCreate(icicle);}writeEventLog(LOG_AM_ON_CREATE_CALLED, "performCreate");mActivityTransitionState.readState(icicle);mVisibleFromClient = !mWindow.getWindowStyle().getBoolean(com.android.internal.R.styleable.Window_windowNoDisplay, false);mFragments.dispatchActivityCreated();mActivityTransitionState.setEnterActivityOptions(this, getActivityOptions());dispatchActivityPostCreated(icicle);}

代码跟到了Activity的onCreate方法,那onStart和onResume呢? 继续来看序号4: execute方法中的executeLifecycleState方法.

android.app.servertransaction.TransactionExecutor

11. executeLifecycleState()

这段代码首先会取出lifecycleItem,而它是在第二阶段(序号15.realStartActivityLocked方法)中设置进去的,即ResumeActivityItem.所以这里会执行ResumeActivityItem对象的execute方法,ResumeActivityItem跟之前的LaunchActivityItem类似,所以执行lifecycleItem.execute最后也会调用到Activity的onResume方法,所以这里就不贴出来调用过程了.

在跟回调onResume方法的代码过程中,看到ActivityThread的handleResumeActivity方法里面会获取Activity的DecorView的过程.

private void executeLifecycleState(ClientTransaction transaction) {final ActivityLifecycleItem lifecycleItem = transaction.getLifecycleStateRequest();if (lifecycleItem == null) {// No lifecycle request, return early.return;}final IBinder token = transaction.getActivityToken();final ActivityClientRecord r = mTransactionHandler.getActivityClient(token);if (DEBUG_RESOLVER) {Slog.d(TAG, tId(transaction) + "Resolving lifecycle state: "+ lifecycleItem + " for activity: "+ getShortActivityName(token, mTransactionHandler));}if (r == null) {// Ignore requests for non-existent client records for now.return;}// Cycle to the state right before the final requested state.cycleToPath(r, lifecycleItem.getTargetState(), true /* excludeLastState */, transaction);// Execute the final transition with proper parameters.lifecycleItem.execute(mTransactionHandler, token, mPendingActions);lifecycleItem.postExecute(mTransactionHandler, token, mPendingActions);}

12. cycleToPath(ActivityClientRecord, int, boolean, ClientTransaction)

13. performLifecycleSequence(ActivityClientRecord, IntArray, ClientTransaction)

跟到这里,Activity onStart生命周期的回调就找到了.

/** Transition the client through previously initialized state sequence. */private void performLifecycleSequence(ActivityClientRecord r, IntArray path,ClientTransaction transaction) {final int size = path.size();for (int i = 0, state; i < size; i++) {state = path.get(i);if (DEBUG_RESOLVER) {Slog.d(TAG, tId(transaction) + "Transitioning activity: "+ getShortActivityName(r.token, mTransactionHandler)+ " to state: " + getStateName(state));}switch (state) {case ON_CREATE:mTransactionHandler.handleLaunchActivity(r, mPendingActions,null /* customIntent */);break;case ON_START:mTransactionHandler.handleStartActivity(r, mPendingActions);break;case ON_RESUME:mTransactionHandler.handleResumeActivity(r.token, false /* finalStateRequest */,r.isForward, "LIFECYCLER_RESUME_ACTIVITY");break;case ON_PAUSE:mTransactionHandler.handlePauseActivity(r.token, false /* finished */,false /* userLeaving */, 0 /* configChanges */, mPendingActions,"LIFECYCLER_PAUSE_ACTIVITY");break;case ON_STOP:mTransactionHandler.handleStopActivity(r.token, false /* show */,0 /* configChanges */, mPendingActions, false /* finalStateRequest */,"LIFECYCLER_STOP_ACTIVITY");break;case ON_DESTROY:mTransactionHandler.handleDestroyActivity(r.token, false /* finishing */,0 /* configChanges */, false /* getNonConfigInstance */,"performLifecycleSequence. cycling to:" + path.get(size - 1));break;case ON_RESTART:mTransactionHandler.performRestartActivity(r.token, false /* start */);break;default:throw new IllegalArgumentException("Unexpected lifecycle state: " + state);}}}

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