為什么在銷毀活動時調用 onRestoreInstanceState 以獲取視圖？

Question

在下面的堆棧跟蹤中，您可以注意到，由於 Activity 被銷毀，視圖的 onRestoreInstanceState 被調用。 為什么這是必要的？

    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

編輯：

View.onRestoreInstanceState接收任何View.onSaveInstanceState產生。 onSaveInstanceState 的文檔說：“鈎子允許視圖生成其內部狀態的表示，以后可用於創建具有相同狀態的新實例。” - 當執行 onDestroy 時，不需要重新創建視圖，那么為什么要調用 onRestoreInstanceState 呢？

Answer 1

您的Fragment的onRestoreInstanceState作為Activity的onDestroy的一部分發生。

這是FragmentManagerImpl的行為：

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;
    }
}

如果片段的狀態被改變（移動）並且片段的視圖不為空，那么作為這個過程的一部分，restoreViewState 總是被調用。

也許您沒有將super.onDestroy()稱為onDestroy的第一條語句？

Answer 2

我想問題應該是：為什么片段銷毀后savedInstanceState不為null ？