很多app都會將返回鍵模擬成home效果，代碼如下：

@Override

public boolean onKeyDown(int keyCode, KeyEvent event) {

if (keyCode == KeyEvent.KEYCODE_BACK) {

IntentWrapper.onBackPressed(this);

moveTaskToBack(true);

}

return true;

}

return super.onKeyDown(keyCode, event);

}

這是之前寫的代碼，但是在bugtags統(tǒng)計上出現(xiàn)很多異常：

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.android.server.am.TaskRecord.setTaskToReturnTo(int)' on a null object reference at android.os.Parcel.readException(Parcel.java:1565)

at android.os.Parcel.readException(Parcel.java:1512)

at android.app.ActivityManagerProxy.moveActivityTaskToBack(ActivityManagerNative.java:3291)

at android.app.Activity.moveTaskToBack(Activity.java:5088)

at com.icourt.alpha.activity.MainActivity.onKeyDown(MainActivity.java)

at android.view.KeyEvent.dispatch(KeyEvent.java:2651)

at android.app.Activity.dispatchKeyEvent(Activity.java:2785)

at android.support.v7.app.AppCompatActivity.dispatchKeyEvent(AppCompatActivity.java)

at android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java)

at android.support.v7.app.AppCompatDelegateImplBase$AppCompatWindowCallbackBase.dispatchKeyEvent(AppCompatDelegateImplBase.java)

at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:2331)

at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:4230)

at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4184)

at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3724)

at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3787)

at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3743)

at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3870)

at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3751)

at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3927)

at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3724)

at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3787)

at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3743)

at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3751)

at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3724)

at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3787)

at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3743)

at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3903)

at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:4064)

at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:2218)

at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:1859)

at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:1850)

at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:2195)

at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:141)

at android.os.MessageQueue.nativePollOnce(Native Method)

at android.os.MessageQueue.next(MessageQueue.java:150)

at android.os.Looper.loop(Looper.java:139)

at android.app.ActivityThread.main(ActivityThread.java:5532)

at java.lang.reflect.Method.invoke(Native Method)

at java.lang.reflect.Method.invoke(Method.java:372)

at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:964)

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:759)

在MainActivity.onKeyDown這個方法中出現(xiàn)的異常，看源碼：

/**

* Move the task containing this activity to the back of the activity

* stack. The activity's order within the task is unchanged.

*

* @param nonRoot If false then this only works if the activity is the root

* of a task; if true it will work for any activity in

* a task.

*

* @return If the task was moved (or it was already at the

* back) true is returned, else false.

*/

public boolean moveTaskToBack(boolean nonRoot) {

try {

return ActivityManagerNative.getDefault().moveActivityTaskToBack(

mToken, nonRoot);

} catch (RemoteException e) {

// Empty

}

return false;

}

大概意思是說，nonRoot 為 false 時，當(dāng)前activity必須為棧底，也就是最底層的activity，如果其他activity沒有及時finish掉，就會出現(xiàn)異常，導(dǎo)致崩潰；nonRoot 為 true 時，不需要考慮當(dāng)前activity是否在棧底。看完源碼瞬間柳暗花明又一村，nice。

在這記錄一下，出現(xiàn)的手機機型：android 5.1.1 (22)，OPPO:OPPO R7sm:arm64-v8a 特別注意！！！

補充說明：

經(jīng)過反復(fù)測試，如果設(shè)置為true，簽名打包之后會失效：

在第一次安裝后，activity管理棧似乎對進(jìn)入的activity不做任何判斷與標(biāo)記(是否是棧頂?shù)腶ctivity)，每次都會入棧，在將棧清空后又回復(fù)正常(就是Task對activity做記錄了，哪個處于棧頂，是否在棧里等)；

1、moveTaskToBack(true);不判斷當(dāng)前activity是否在棧底

2、moveTaskToBack(false);先判斷當(dāng)前activity是否在棧底

再根據(jù)第一次安裝，如果設(shè)為true，每次點擊icon，都會重啟app，如果設(shè)為false，則會找到棧內(nèi)的activity，直接顯示。

最終代碼：

@Override

public boolean onKeyDown(int keyCode, KeyEvent event) {

if (keyCode == KeyEvent.KEYCODE_BACK) {

IntentWrapper.onBackPressed(this);

try {

moveTaskToBack(false);

} catch (Exception e) {

bugSync("返回鍵模擬HOME出錯", e);

return super.onKeyDown(keyCode, event);

}

}

return super.onKeyDown(keyCode, event);

}

/**

* 防止華為機型未加入白名單時按返回鍵回到桌面再鎖屏后幾秒鐘進(jìn)程被殺

*/

public static void onBackPressed(Activity a) {

try {

Intent launcherIntent = new Intent(Intent.ACTION_MAIN);

launcherIntent.addCategory(Intent.CATEGORY_HOME);

a.startActivity(launcherIntent);

} catch (Throwable e) {

e.printStackTrace();

}

}

總結(jié)

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