Fragment系列之Can not perform this action after onSaveInstanceState

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使用fragment过程当中产生异常的日志信息：

java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
at android.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1109)
at android.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:399)
at android.app.Activity.onBackPressed(Activity.java:2066)
at android.app.Activity.onKeyUp(Activity.java:2044)
at android.view.KeyEvent.dispatch(KeyEvent.java:2529)
at android.app.Activity.dispatchKeyEvent(Activity.java:2274)
......

从日志信息我们可以定位到onSaveInstanceState()方法，可以了解到异常原因：在onSaveInstanceState行为之后，app执行某个不能响应的行为而导致异常发生。

stackoverflow上有个解释：

Please check my answer here. Basically I just had to :@Override
protected void onSaveInstanceState(Bundle outState) {//No call for super(). Bug on API Level > 11.
}
Don't make the call to super() on the saveInstanceState method. This was messing things up...This is a known bug in the support package.If you need to save the instance and add something to your outState Bundle you can use the following:@Override
protected void onSaveInstanceState(Bundle outState) {outState.putString("WORKAROUND_FOR_BUG_19917_KEY", "WORKAROUND_FOR_BUG_19917_VALUE");super.onSaveInstanceState(outState);
}
In the end the proper solution was (as seen in the comments) to use :transaction.commitAllowingStateLoss();
when adding or performing the FragmentTransaction that was causing the Exception.

意思就是：当Activity销毁前调用onSaveInstanceState()方法之后，我们就不能添加或者执行FragmentTransaction ，会导致异常。“This was messing things up…”意思是这样做会丢失状态值可能导致UI状态丢失。（场景：“内存重启”有疑问参见上一篇博文）

解决方案

上文已经贴出来了，建议尽量在 super.onSaveInstanceState(outState)方法之前添加数据，使用commitAllowingStateLoss()替换commit()提交事务，允许状态丢失的提交。（恰巧Activity被强杀时可能导致该次提交无效）
请参考你可能漏掉的知识点: onResumeFragments
这里处理的方法就是保存期它的FragmentTransaction 对象等Activity重新恢复的时候再执行事务，能确保事务不会丢失。

@Override// 如果是在Fragment内， 则复写onResumeFragments()改为onResume()即可protected void onResumeFragments() {super.onResumeFragments();if (mTransactionEvent != null) {// 这里执行事务mTransactionEvent = null;}}@Overrideprotected void onSaveInstanceState(Bundle outState) {super.onSaveInstanceState(outState);//保存事务 给mTransactionEvent赋值}