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Activity
		options = 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 onCreate
    final 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);
}