Android四大组件的启动

四大组件的启动

Activity的启动

1.startActivity

• 通常使用startActivity函数来启动一个Activity

public void startActivity(Intent intent) {this.startActivity(intent ,null);
}public void startActivity(Intent intent, @Nullable Bundle options) {...if (options != null) {startActivityForResult(intent, -1, options);else {startActivityForResult(intent, -1);}
}pulic void startActivityForResult(Intent intent, int requestCode) {startActivityForResult(intent, requestCode, null);
}

2.startActivityForResult

public void startActivityForResult(Intent intent, int requestCode, Bundle options) {if (mParent == null) { // 应用第一次创建Activity, 此时不存在父类的Activityoptions = transferSpringboardActivityOptions(options);Instrumenttation.execStartActivity(this, mMainTread.getApplicationThread(), mToken, this, intent, requestCode, options);else {if (options != null) {mParents.startActivityFromChild(this, intent, requestCode, options);} else {mParents.startActivityFromChidl(this, intent, requestCode);}}

3.Instrumentation.execStartActivity

• 这个工具类用来监视应用进程和系统交互的，调用该方法，其内部实际调用了ActivityTaskManager.getService().startActivity函数，这个类是在SystemServer里面的，看到这个进程，就知道这是个系统级别的东西，很重要

public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, Activity tartget, Intent intent, Int requestCode, Bundle otions) {IApplicationTread whoThread = (IApplicationThread) contextThread;...try {int result = ActivityTaskManager.getService().startActivity(.......);} catch (RemoteException e) {.......return null;
}

4.ATMS.startActivity

• ATMS就是ActivityTaskManagerService
• 类似的ConnectivityManager, ConnectivityService, 都是在Manager中定义一堆接口，然后在service中是具体的实现

pulic int startActivityAsUser(......) {return startActivityAsUser(........, UserHandle.getCallingUserId());
}

• 这个函数的作用就是检查包名和userId是否一致等安全权限问题

pulic int startActivityAsUser(........., int userId) {return startActivityAsUser(..........,userId, true);
}pulic int startActivityAsUser(........., int userId, boolean validateIncomingUser) {asserPackageMatchesCallingUid(callingPackage);enforceNotIsolatedCaller("startActivityAsUser");// 上面两个是一堆检查，没什么必要了解return getActivityStartController().obtainStarter(intent, "startActivityAsUser").setCaller(caller).setCallingPackage(callingPackage).setCallingFeatureId(callingFeatureId)...........setUser(userId).execute();
}

5.ActivityStarter.execute

• execute -> executRequest
• 因为内部代码比较复杂，这里就不放，总之干了一件事，把上面含有一堆信息Build出的对象，封装成了一个ActivityRecord 对象，然后调用它的startActivityUnchecked方法

pulic int startActivityUnchecked(.........) {int result = START_CANCELED;..........result = startActivityInner(.......);.........return result;
}int startActivityInner(...........) {.......mRootWindowContainer.resumeFocusedStacksTopActivities(......)return START_SUCCESS;
}

6.中间的一系列省略掉，最后调用了Activity.performCreate

final void performCreate(Bundle icicle, PersistableBundle persistentState) {dispatchActivityPreCreated(icicle);mCanEnterPictureInPicture = true;// initialize mIsInMultiWindowMode and mIsInPictureInPictureMode before onCreatefinal int windowingMode = getResources().getConfiguration().windowConfiguration.getWindowingMode();mIsInMultiWindowMode = inMultiWindowMode(windowingMode);mIsInPictureInPictureMode = windowingMode == WINDOWING_MODE_PINNED;restoreHasCurrentPermissionRequest(icicle);if (persistentState != null) {onCreate(icicle, persistentState);} else {onCreate(icicle);}EventLogTags.writeWmOnCreateCalled(mIdent, getComponentName().getClassName(),"performCreate");mActivityTransitionState.readState(icicle);mVisibleFromClient = !mWindow.getWindowStyle().getBoolean(com.android.internal.R.styleable.Window_windowNoDisplay, false);mFragments.dispatchActivityCreated();mActivityTransitionState.setEnterActivityOptions(this, getActivityOptions());dispatchActivityPostCreated(icicle);
}