解决 IllegalStateException: Can not perform this action after onSaveInstanceState

今天在修复外网崩溃时，发现有这个错误 IllegalStateException: Can not perform this action after onSaveInstanceState，详细堆栈信息如下：

java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager:1377) at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager:504) at android.support.v4.app.FragmentActivity.onBackPressed(FragmentActivity:178) at android.app.Activity.onKeyUp(Activity.java:2207) at android.view.KeyEvent.dispatch(KeyEvent.java:2664) at android.app.Activity.dispatchKeyEvent(Activity.java:2437) at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1975) at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:4013) at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3987) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3553) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3603) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3572) at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3679) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3580) at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3736) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3553) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3603) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3572) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3580) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3553) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3603) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3572) at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3712) at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:3877) at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:2027) at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:1721) at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:1712) at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:2004) at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:141) at android.os.MessageQueue.nativePollOnce(Native Method) at android.os.MessageQueue.next(MessageQueue.java:138) at android.os.Looper.loop(Looper.java:123) at android.app.ActivityThread.main(ActivityThread.java:5028) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:788) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:604) at dalvik.system.NativeStart.main(Native Method) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 通过堆栈信息可以看出，异常是发生在onBackPressed时，发现onSaveInstanceState 方法被调用了。了解异常如何产生，首先必须弄明白onSaveInstanceState方法的调用时机，onSaveInstanceState api 介绍如下： onSaveInstanceState api

概括的讲，onSaveInstanceState 这个方法会在activity 将要被kill之前被调用以保存每个实例的状态，以保证在将来的某个时刻回来时可以恢复到原来的状态，但和activity 的生命周期方法onStop 和 onPause 不一样，与两者并没有绝对的先后调用顺序，或者说并非所有场景都会调用onSaveInstanceState 方法。那么onSaveInstanceState 方法何时会被调用呢，或者这么问，什么时候activity 会被系统kill 掉呢？有以下几种比较常见的场景：（1）用户主动按下home 键，系统不能确认activity 是否会被销毁，实际上此刻系统也无法预测将来的场景，比如说内存占用，应用运行情况等，所以系统会调用onSaveInstanceState保存activity状态；（2）activity位于前台，按下电源键，直接锁屏；（3）横竖屏切换；（4）activity B启动后位于activity A之前，在某个时刻activity A因为系统回收资源的问题要被kill掉，A通过onSaveInstanceState保存状态。

那么，为什么会抛出异常呢？原因在于我们的activity在某种场景下处于被kill 掉的边缘，系统就调用了onSaveInstanceState 方法，这个方法里面会调用 FragmentManager saveAllState 方法，将fragment 的状态保存，在状态保存后用户又主动调了 onBackPressed ，而这个方法的超类super.onBackPressed 方法会判断FragmentManager 是否保存了状态，如果已经保存就会抛出IllegalStateException 的异常。

此外，还有一个比较类似的异常堆栈信息：

最后，谈谈如何避免这一类的崩溃问题。 1、关于commit 方法的调用异常处理方法（1）在activity生命周期函数内谨慎使用commit 方法，一般情况下如果能在onCreate 中调用，基本不会出现问题，但是如果在onResume onStart 等方法中调用就需要格外注意，比如说FragmetActivity 的onResume 方法，在某些场景下onResume 方法被调用之前，可能依然保存着之前的状态导致异常。

Dispatch onResume() to fragments. Note that for better inter-operation with older versions of the platform, at the point of this call the fragments attached to the activity are not resumed. This means that in some cases the previous state may still be saved, not allowing fragment transactions that modify the state. 1 2 3 （2）尽可能避免在一些和生命周期函数异步的方法中调用commit，如AsyncTask 等。（3）实在没法确定调用时机时，可以用commitAllowingStateLoss 代替 commit ，commitAllowingStateLoss 在状态丢失时不会抛出任何异常，但也正因为如此在一些必须确保状态被保存的场合，最好不要使用 commitAllowingStateLoss 方法。

2、针对onbackpress 导致的异常，也有几种解决手段（1）在api11 以上不调用super 的onSaveInstanceState 方法

protected void onSaveInstanceState(Bundle outState) { //No call for super(). Bug on API Level > 11. } 1 2 3 这样做的后果会导致activity 和 fragment 的所有状态，在activity 被系统杀死掉后无法保存，所以如果有保存状态的需要，这个方法是不适用的。

（2）重写 onBackPressed 方法，不调用super.onBackPressed ,直接调用finish 。原因很简单，super.onBackPressed 里面会调用FragmentManager popBackStackImmediate() 方法，如果直接掉finish 就不会触发异常，但这种情况只建议在没有使用 Fragments api时调用。

（3）通过反射手段在onSaveInstanceState 方法里调用 FragmentManagerImpl noteStateNotSaved方法将 mStateSaved 变量置为false ，这样既不会导致activity状态丢失，也能确保退出时不会抛出异常，算是比较优雅的处理途径，代码如下：

private Method noteStateNotSavedMethod;
private Object fragmentMgr;
private String[] activityClassName = {"Activity", "FragmentActivity"};

[@Override](https://my.oschina.net/u/1162528)
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    invokeFragmentManagerNoteStateNotSaved();
}

private void invokeFragmentManagerNoteStateNotSaved() {
    //java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
        return;
    }
    try {
        if (noteStateNotSavedMethod != null && fragmentMgr != null) {
            noteStateNotSavedMethod.invoke(fragmentMgr);                
            return;
        }
        Class cls = getClass();
        do {
            cls = cls.getSuperclass();
        } while (!(activityClassName[0].equals(cls.getSimpleName())
                || activityClassName[1].equals(cls.getSimpleName())));

        Field fragmentMgrField = prepareField(cls, "mFragments");
        if (fragmentMgrField != null) {
            fragmentMgr = fragmentMgrField.get(this);
            noteStateNotSavedMethod = getDeclaredMethod(fragmentMgr, "noteStateNotSaved");
            if (noteStateNotSavedMethod != null) {
                noteStateNotSavedMethod.invoke(fragmentMgr);                    
            }
        }

    } catch (Exception ex) {            
    }
}

private Field prepareField(Class<?> c, String fieldName) throws NoSuchFieldException {
    while (c != null) {
        try {
            Field f = c.getDeclaredField(fieldName);
            f.setAccessible(true);
            return f;
        } finally {
            c = c.getSuperclass();
        }
    }
    throw new NoSuchFieldException();
}

private Method getDeclaredMethod(Object object, String methodName, Class<?>... parameterTypes) {
    Method method = null;
    for (Class<?> clazz = object.getClass(); clazz != Object.class; clazz = clazz.getSuperclass()) {
        try {
            method = clazz.getDeclaredMethod(methodName, parameterTypes);
            return method;
        } catch (Exception e) {
        }
    }
    return null;
}

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 到这里已经介绍完了，如果对于文章内容有兴趣的话，可以多多交流。

解决 IllegalStateException: Can not perform this action after onSaveInstanceState

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