为什么在销毁活动时调用 onRestoreInstanceState 以获取视图？

Question

在下面的堆栈跟踪中，您可以注意到，由于 Activity 被销毁，视图的 onRestoreInstanceState 被调用。 为什么这是必要的？

    at com.mypackage.MyView.onRestoreInstanceState(Unknown Source)
    at android.view.View.dispatchRestoreInstanceState(View.java:13758)
    at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2889)
    at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2895)
    at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2895)
    at android.view.View.restoreHierarchyState(View.java:13736)
    at android.support.v4.app.Fragment.restoreViewState(Unknown Source)
    at android.support.v4.app.FragmentManagerImpl.moveToState(Unknown Source)
    at android.support.v4.app.FragmentManagerImpl.moveToState(Unknown Source)
    at android.support.v4.app.FragmentManagerImpl.moveToState(Unknown Source)
    at android.support.v4.app.FragmentManagerImpl.dispatchReallyStop(Unknown Source)
    at android.support.v4.app.FragmentActivity.onReallyStop(Unknown Source)
    at android.support.v4.app.FragmentActivity.doReallyStop(Unknown Source)
    at android.support.v4.app.FragmentActivity.onDestroy(Unknown Source)
    at android.support.v7.app.o.onDestroy(Unknown Source)
    at android.app.Activity.performDestroy(Activity.java:6189)
    at android.app.Instrumentation.callActivityOnDestroy(Instrumentation.java:1164)
    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3778)
    ... 10 more

编辑：

View.onRestoreInstanceState接收任何View.onSaveInstanceState产生。 onSaveInstanceState 的文档说：“钩子允许视图生成其内部状态的表示，以后可用于创建具有相同状态的新实例。” - 当执行 onDestroy 时，不需要重新创建视图，那么为什么要调用 onRestoreInstanceState 呢？

Answer 1

您的Fragment的onRestoreInstanceState作为Activity的onDestroy的一部分发生。

这是FragmentManagerImpl的行为：

void moveToState(Fragment f, int newState, int transit, int transitionStyle, boolean keepActive) {
    //...
    case Fragment.CREATED:
    if (newState > Fragment.CREATED) {
    //...
        f.performActivityCreated(f.mSavedFragmentState);
        if (f.mView != null) {
            f.restoreViewState(f.mSavedFragmentState);
        }
        f.mSavedFragmentState = null;
    }
}

如果片段的状态被改变（移动）并且片段的视图不为空，那么作为这个过程的一部分，restoreViewState 总是被调用。

也许您没有将super.onDestroy()称为onDestroy的第一条语句？

Answer 2

我想问题应该是：为什么片段销毁后savedInstanceState不为null ？