saveInstanceState 始终为空

Question

我目前有一个附加到活动的片段。当我旋转我的设备时，希望在再次创建视图时保存和恢复网格的详细信息和位置。 onSavedStateInstance() 运行良好，我捆绑了所有内容，但是当调用片段的onCreateView() 时，stateInstance 为null。我知道之前有人问过并回答过类似的问题，但对我来说并没有真正的帮助。以下是一些可能对调试有用的 sn-ps。

MainActivityFragment

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.fragment_main, container, false);

    if (savedInstanceState != null) {
        gridViewObjects = (List<GridViewObject>) savedInstanceState.get(movieKey);
        position = savedInstanceState.getInt("position");
    } else {
        gridViewObjects = new ArrayList<>();
    }
    return view;
}

@Override
public void onSaveInstanceState(Bundle outState) {
    outState.putParcelableArrayList(movieKey, (ArrayList) gridViewObjects);
    outState.putInt("position", gridView.getFirstVisiblePosition());
    super.onSaveInstanceState(outState);
}

fragment_main.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="app.sunshine.android.example.com.popmovies.MainActivityFragment">

    <GridView
        android:id="@+id/fragment_main_gridView"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:clickable="true"
        android:gravity="center"
        android:numColumns="2"
        android:stretchMode="columnWidth"
        android:verticalSpacing="5dp" />

</FrameLayout>

主活动

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ActionBar actionBar = getSupportActionBar();
    actionBar.setBackgroundDrawable(new ColorDrawable(getResources().getColor(R.color.indigo_500)));
    setContentView(R.layout.activity_main);
}

编辑：在调试时，我看到在设备方向更改时，活动被重新创建，OnCreate() 方法中的 savedInstanceState 不为空。捆绑包详细信息完好无损。只有在创建fragment时，OnCreateView()中的savedInstanceState为null。

任何帮助表示赞赏！

Answer 1

试试这个

@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
  super.onRestoreInstanceState(savedInstanceState);    

         if (savedInstanceState != null) {
            gridViewObjects = (List<GridViewObject>) savedInstanceState.get(movieKey);
            position = savedInstanceState.getInt("position");
        } else {
            gridViewObjects = new ArrayList<>();
        }
    }

还有

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.fragment_main, null);
    return view;
}

Answer 2

在片段中，通过覆盖onSaveInstanceState保存实例状态并在onActivityCreated上恢复：

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    ...
    if (savedInstanceState != null) {
        //Restore the fragment's state here
    }
}
...
@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

//Save the fragment's state here



}

很重要的一点，在活动中，你必须将片段的实例保存在onSaveInstanceState并恢复到onCreate。

public void onCreate(Bundle savedInstanceState) {
    ...
    if (savedInstanceState != null) {
        //Restore the fragment's instance
        mContent = getSupportFragmentManager().getFragment(
                    savedInstanceState, "mContent");
        ...
    }
    ...
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

//Save the fragment's instance
getSupportFragmentManager().putFragment(outState, "mContent", mContent);



}

所以要正确保存 Fragment 的实例状态，您应该执行以下代码。