ViewPager+Fragment 或者 按钮切换Fragme引发的错误：No Activity

1.bug的log
java.lang.IllegalStateException: No activity
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1075)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1070)
at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1861)
at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1474)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:931)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:461)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1011)
at android.support.v4.view.ViewPager.populate(ViewPager.java:880)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1374)

2.出现场景
第一次启动程序能够正常运行，随便切换tab也不会有问题，第二次必崩！

3.bug出现的原理及如何修复
This seems to be a bug in the newly added support for nested fragments. Basically, the child FragmentManager ends up with a broken internal state when it is detached from the activity. A short-term workaround that fixed it for me is to add the following to onDetach() of every Fragment which you call getChildFragmentManager() on:

@Override
public void onDetach() {
super.onDetach();

1 2 3 4 5 6 7 8 9 10

try {    Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");    childFragmentManager.setAccessible(true);    childFragmentManager.set(this, null); } catch (NoSuchFieldException e) {    throw new RuntimeException(e); } catch (IllegalAccessException e) {    throw new RuntimeException(e); }

}

4.是什么引发的bug
If you look at the implementation of Fragment, you'll see that when moving to the detached state, it'll reset its internal state. However, it doesn't reset mChildFragmentManager (this is a bug in the current version of the support library). This causes it to not reattach the child fragment manager when the Fragment is reattached, causing the exception you saw.

参考资料：http://stackoverflow.com/questions/15207305/getting-the-error-java-lang-illegalstateexception-activity-has-been-destroyed