Framework学习系列第一篇｜基于Android 13分析几个特殊场景下的Activity启动流程背景在唤端过程中

背景

在唤端过程中有个有趣的现象。同一个 activity Task

Activity A打开B接着打开C

打开B间隔一段时间打开C,按顺序正常走B和C的onCreate 和onResume
打开B和C的时间很接近只会走C的 onCreate 和onResume, 按返回键走到B的onCreate和onResume
1的状态下在后台去打开B和C B和C均不走生命周期方法 ,回到前台走到C的onCreate 和onResume，按返回键走到B的onCreate和onResume
2的状态下代码内finish A，然后在后台5s内去打开B和C ，C会被直接调起走C的 onCreate 和onResume。

分析

基于Android 13.0.0-r11源码调试分析

场景1

走正常的acitivity 启动流程按顺序启动B和启动C

未命名文件 (3).jpg

场景2

相对于场景1 两个activity启动时间接近。启动第二个activity C时 C加入了Task 但是没通过allPausedActivitiesComplete 所以没有走后续相关流程，resumeTopActivity时获取到Top的activity是C 所以走了C的生命周期 B就没有走了等点击返回键时resumeTopActivity获取到了B又走了一遍B的生命周期。

final boolean allPausedComplete = mRootWindowContainer.allPausedActivitiesComplete();

if (!allPausedComplete) {

ProtoLog.v(WM_DEBUG_STATES,

"resumeTopActivity: Skip resume: some activity pausing.");

return false;

}

场景3

应用在后台调用startActivity时并不会去创建对应Activity，在system_server进程会有是否允许后台进程启动activity的判断 shouldAbortBackgroundActivityStart ****如果不允许，把Activity加入相应task后就不去走相应Acitivity的流程了，在这个例子中按顺序把B和C加入Task, 点击app icon后，home进程调用startActivity A resumeTopActivity后发现C在最上层就会先去走C的创建和生命周期流程，点击返回键后发现B在最上层就去走B的创建和生命周期流程

未命名文件 (3).png

场景4

有几个关键字段

lastActivityLaunchTime：A Activity的Launch时间

lastActivityFinishTime: A Activity的finish时间

lastStopAppSwitchesTime:这个字段是全局的任意 app 按home键都会更新这个时间

条件1:当前时间不超过lastActivityLaunchTime或者不超过lastActivityFinishTime时间的10s

条件2: lastActivityLaunchTime或lastActivityFinishTime之后没有更改lastStopAppSwitchesTime

满足上面两个条件 activity能够正常起来。

if (appSwitchState == APP_SWITCH_ALLOW) {
    // Allow if any activity in the caller has either started or finished very recently, and
    // it must be started or finished after last stop app switches time.
    final long now = SystemClock.uptimeMillis();
    if (now - lastActivityLaunchTime < ACTIVITY_BG_START_GRACE_PERIOD_MS
            || now - lastActivityFinishTime < ACTIVITY_BG_START_GRACE_PERIOD_MS) {
        // If activity is started and finished before stop app switch time, we should not
        // let app to be able to start background activity even it's in grace period.
        if (lastActivityLaunchTime > lastStopAppSwitchesTime
                || lastActivityFinishTime > lastStopAppSwitchesTime) {
            if (DEBUG_ACTIVITY_STARTS) {
                Slog.d(TAG, "[Process(" + pid
                        + ")] Activity start allowed: within "
                        + ACTIVITY_BG_START_GRACE_PERIOD_MS + "ms grace period");
            }
            return true;
        }
        if (DEBUG_ACTIVITY_STARTS) {
            Slog.d(TAG, "[Process(" + pid + ")] Activity start within "
                    + ACTIVITY_BG_START_GRACE_PERIOD_MS
                    + "ms grace period but also within stop app switch window");
        }

    }
}

堆栈记录

System_server进程 startActivity调用堆栈

        at com.android.server.wm.TaskFragment.schedulePauseActivity(TaskFragment.java:1665)
        at com.android.server.wm.TaskFragment.startPausing(TaskFragment.java:1608)
        at com.android.server.wm.TaskFragment.resumeTopActivity(TaskFragment.java:1198)
        at com.android.server.wm.Task.resumeTopActivityInnerLocked(Task.java:5003)
        at com.android.server.wm.Task.resumeTopActivityUncheckedLocked(Task.java:4938)
        at com.android.server.wm.RootWindowContainer.resumeFocusedTasksTopActivities(RootWindowContainer.java:2260)
        at com.android.server.wm.ActivityStarter.startActivityInner(ActivityStarter.java:1935)
        at com.android.server.wm.ActivityStarter.startActivityUnchecked(ActivityStarter.java:1661)
        at com.android.server.wm.ActivityStarter.executeRequest(ActivityStarter.java:1216)
        at com.android.server.wm.ActivityStarter.execute(ActivityStarter.java:702)
        at com.android.server.wm.ActivityTaskManagerService.startActivityAsUser(ActivityTaskManagerService.java:1260)
        at com.android.server.wm.ActivityTaskManagerService.startActivityAsUser(ActivityTaskManagerService.java:1223)
        at com.android.server.wm.ActivityTaskManagerService.startActivity(ActivityTaskManagerService.java:1198)
        at android.app.IActivityTaskManager$Stub.onTransact(IActivityTaskManager.java:893)
        at com.android.server.wm.ActivityTaskManagerService.onTransact(ActivityTaskManagerService.java:5222)
        at android.os.Binder.execTransactInternal(Binder.java:1280)
        at android.os.Binder.execTransact(Binder.java:1244)

System_server进程 com.android.server.wm.Task addChild调用堆栈

        at com.android.server.wm.WindowContainer.addChild(WindowContainer.java:742)
        at com.android.server.wm.TaskFragment.addChild(TaskFragment.java:1835)
        at com.android.server.wm.Task.addChild(Task.java:1429)
        at com.android.server.wm.ActivityStarter.addOrReparentStartingActivity(ActivityStarter.java:2927)
        at com.android.server.wm.ActivityStarter.startActivityInner(ActivityStarter.java:1866)
        at com.android.server.wm.ActivityStarter.startActivityUnchecked(ActivityStarter.java:1661)
        at com.android.server.wm.ActivityStarter.executeRequest(ActivityStarter.java:1216)
        at com.android.server.wm.ActivityStarter.execute(ActivityStarter.java:702)
        at com.android.server.wm.ActivityTaskManagerService.startActivityAsUser(ActivityTaskManagerService.java:1260)
        at com.android.server.wm.ActivityTaskManagerService.startActivityAsUser(ActivityTaskManagerService.java:1223)
        at com.android.server.wm.ActivityTaskManagerService.startActivity(ActivityTaskManagerService.java:1198)
        at android.app.IActivityTaskManager$Stub.onTransact(IActivityTaskManager.java:893)
        at com.android.server.wm.ActivityTaskManagerService.onTransact(ActivityTaskManagerService.java:5222)
        at android.os.Binder.execTransactInternal(Binder.java:1280)
        at android.os.Binder.execTransact(Binder.java:1244)

System_server进程 activityPaused调用堆栈

        at com.android.server.wm.ActivityTaskSupervisor.realStartActivityLocked(ActivityTaskSupervisor.java:924)
        at com.android.server.wm.ActivityTaskSupervisor.startSpecificActivity(ActivityTaskSupervisor.java:1042)
        at com.android.server.wm.TaskFragment.resumeTopActivity(TaskFragment.java:1483)
        at com.android.server.wm.Task.resumeTopActivityInnerLocked(Task.java:5003)
        at com.android.server.wm.Task.resumeTopActivityUncheckedLocked(Task.java:4938)
        at com.android.server.wm.RootWindowContainer.resumeFocusedTasksTopActivities(RootWindowContainer.java:2260)
        at com.android.server.wm.RootWindowContainer.resumeFocusedTasksTopActivities(RootWindowContainer.java:2246)
        at com.android.server.wm.TaskFragment.completePause(TaskFragment.java:1735)
        at com.android.server.wm.ActivityRecord.activityPaused(ActivityRecord.java:5992)
        at com.android.server.wm.ActivityClientController.activityPaused(ActivityClientController.java:178)
        at android.app.IActivityClientController$Stub.onTransact(IActivityClientController.java:574)
        at com.android.server.wm.ActivityClientController.onTransact(ActivityClientController.java:124)
        at android.os.Binder.execTransactInternal(Binder.java:1280)
        at android.os.Binder.execTransact(Binder.java:1244)

总结

事实上调用startActivity后，还是需要很多个步骤才能去完成activity的创建以及生命周期流程的走完，平常开发时也需要注意一些细节，比如连续调用两个activity 可能是后面的activity更早创建，如果有些逻辑依赖了前一个activity就可能出现问题。