Fragment系列之Can not perform this action after onSaveInstanceState

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 onSaveInstanceStateat 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 :@Overrideprotected 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:@Overrideprotected 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

1. 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）

2. 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;        }    }    @Override    protected void onSaveInstanceState(Bundle outState) {        super.onSaveInstanceState(outState);          //保存事务 给mTransactionEvent赋值    }

虽说方案一所说的Activity被强杀情况下没有执行到commitAllowingStateLoss()方法有可能发生，但是概率很低，我们使用这个方法基本不会有什么问题，方案二虽然麻烦些都是稳一些，用哪个看你自己了。