任务栏清除app导致app不执行onDestory"/>
最近任务栏清除app导致app不执行onDestory
问题
- 步骤:在计算器面板上出入数字,然后按Menu键进入最近任务界面,右滑清楚计算器,接着再进入计算器
- 期望结果:再次进入计算器,上面显示的内容和之前的一致
- 实际结果:没有保存
初步分析
开发计算器的工程师A说保存的代码写在了onDestory内,他说因为计算器的生命周期没有走完酒杯杀掉了,觉得是系统的问题,让系统的工程师看
我看了问题和工程师A的回复,我首先说,保存重要数据,不要保存在onStop和onDestory内,Android开发者文档中也有说明
至于为什么onDestory没有走完,我怀疑是并行的原因,需要在代码里去找证据
具体分析
removeTaskByIdLocked
文件:AMS
private boolean removeTaskByIdLocked(int taskId, boolean killProcess,boolean removeFromRecents) {......if (tr != null) {tr.removeTaskActivitiesLocked(); //清除Task中的activity,见 2cleanUpRemovedTaskLocked(tr, killProcess, removeFromRecents); //清除相关的进程,见3......}return false; }
在最近任务界面右滑时,会调用上面这个方法,里面有两个很重要的方法,分别是removeTaskActivitiesLocked和cleanUpRemovedTaskLocked,我们先来看看removeTaskActivitiesLocked
removeTaskActivitiesLocked
文件:TaskRecord.java
public void removeTaskActivitiesLocked() {// 见2.1performClearTaskAtIndexLocked(0); }
2.1 performClearTaskAtIndexLocked
文件:TaskRecord.java
final void performClearTaskAtIndexLocked(int activityNdx) {int numActivities = mActivities.size();for ( ; activityNdx < numActivities; ++activityNdx) {......else if (stack.finishActivityLocked(r, Activity.RESULT_CANCELED, null, "clear-task-index", false)) {);--activityNdx;--numActivities;}} }
上面会调用finishActivityLocked,我们继续往下看
2.2 finishActivityLocked
文件:ActivityStack.java
final boolean finishActivityLocked(ActivityRecord r, int resultCode, Intent resultData,String reason, boolean oomAdj) { ...... else if (r.state != ActivityState.PAUSING) {......// 见2.3return finishCurrentActivityLocked(r, (r.visible || r.nowVisible) ?FINISH_AFTER_VISIBLE : FINISH_AFTER_PAUSE, oomAdj) == null;}...... }
2.3 finishCurrentActivityLocked
文件:ActivityStack.java
final ActivityRecord finishCurrentActivityLocked(ActivityRecord r, int mode, boolean oomAdj) {......if (mode == FINISH_IMMEDIATELY|| (prevState == ActivityState.PAUSED&& (mode == FINISH_AFTER_PAUSE || mode == FINISH_AFTER_VISIBLE|| mStackId == PINNED_STACK_ID))|| prevState == ActivityState.STOPPED|| prevState == ActivityState.INITIALIZING) {r.makeFinishingLocked();// 见2.4boolean activityRemoved = destroyActivityLocked(r, true, "finish-imm");...... }
2.4 destroyActivityLocked
文件:ActivityStack.java
final boolean destroyActivityLocked(ActivityRecord r, boolean removeFromApp, String reason) { ......try {// 见2.5r.app.thread.scheduleDestroyActivity(r.appToken, r.finishing,r.configChangeFlags);}...... }
马上要开始进行Binder调用了,System Sever这边是客户端,所以接下来是着ApplicationThreadProxy.java中的scheduleDestroyActivity
2.5 scheduleDestroyActivity
public final void scheduleDestroyActivity(IBinder token, boolean finishing,int configChanges) throws RemoteException {......mRemote.transact(SCHEDULE_FINISH_ACTIVITY_TRANSACTION, data, null,IBinder.FLAG_ONEWAY);...... }
注意上面的IBinder.FLAG_ONEWAY参数,这说明该binder调用是非阻塞的,这样问题可以解释的通了,接下来系统进程这边的代码会继续跑,不会等App进程那边的反馈,就当App进程那边准备处理这个SCHEDULE_FINISH_ACTIVITY_TRANSACTION消息时,App已经被杀掉了,所以计算器写在onDestory内的代码也就没有机会执行了
cleanUpRemovedTaskLocked
文件:AMS
private void cleanUpRemovedTaskLocked(TaskRecord tr, boolean killProcess,boolean removeFromRecents) {......// Kill the running processes.for (int i = 0; i < procsToKill.size(); i++) {ProcessRecord pr = procsToKill.get(i);if (pr.setSchedGroup == ProcessList.SCHED_GROUP_BACKGROUND&& pr.curReceiver == null) {pr.kill("remove task", true);} else {// We delay killing processes that are not in the background or running a receiver.pr.waitingToKill = "remove task";}} }
这就是杀进程的方法
时序图
上面的方法中,除了ATN,ApplicationThread,ActivityThread是跑在App进程,其他都跑在System Sever进程
总结
其实前面都已经说了,这里再罗嗦一下,不要在onStop,onDestory中保存重要数据;最近任务栏清除app,app的onDestory不会掉用是因为该Binder调用是非阻塞的,导致App被杀死,所以onDestory没来得及调用
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最近任务栏清除app导致app不执行onDestory
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