在后退按钮上获取 Android 片段的先前状态

Question

在一个 android 应用程序中，我有多个片段，在一个片段（片段 A）中，我使用布尔变量在按钮单击时在 GridView 中的两组图像之间切换。 Th GridView 项目单击导致第二个片段（片段 B）。在 Fragment B 上按下 Back 按钮时，Fragment A 中的 gridview 会加载默认的图像集，而不是在继续下一个 Fragment Fragment B 之前设置的图像。

请指导如何恢复以前的图像集而不是默认图像集？

在 MainActivity 中，我在 BackPressed 上实现如下：

@Override
    public void onBackPressed() {
        if (frag instanceof SettingsFragment)
            loadGridViewFragment();
        else if (frag instanceof SingleDuaViewPagerFragment) {
            boolean keyIsFavSel = new SharedPreferencesSupplication().read(SingletonClass.keyIsFavSelected, false);
            if (keyIsFavSel)
                loadDuasListFragment();
            else
                loadGridViewFragment();
        }
        else if (frag instanceof DuasListFragment) {
            boolean keyIsFavSel = new SharedPreferencesSupplication().read(SingletonClass.keyIsFavSelected, false);
            if (keyIsFavSel)
                loadGridViewFragment();
            else
                loadSingleDuaFragment();
        }
        else
            super.onBackPressed();
    }

GridViewFragment.java的OnCreate方法

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    //  fragment = new GridViewFragment();
        context = inflater.getContext();
        View view = inflater.inflate(R.layout.fragment_gridview, container, false); 
        ga = new GridViewAdapter(context);
        Btn_lang_Ch = (Button) view.findViewById(R.id.lng_ch);
        Btn_Settings = (Button) view.findViewById(R.id.button_settings);
        favoriteDuas = (Button) view.findViewById(R.id.btn_favorite_duas);
        GridMenu =(GridView) view.findViewById(R.id.gridView1);
    float scalefactor = getResources().getDisplayMetrics().density * 150;
        @SuppressWarnings("deprecation")
        int number = getActivity().getWindowManager().getDefaultDisplay().getWidth();
        int columns = (int) ((float) number / (float) scalefactor);
        GridMenu.setAdapter(ga);
        GridMenu.setNumColumns(columns);    
        setRetainInstance(true);
        return view;

    }

Answer 1

您应该在片段的onCreate 方法中调用setRetainInstance(true) 或在onSaveInstanceState 和onRetainInstanceState 中保存并加载正确的值

编辑：我通常会这样做：

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setRetainInstance(true);
}

private View view;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    if (view == null) {
        context = inflater.getContext();
        view = inflater.inflate(R.layout.fragment_gridview, container, false); 
        ga = new GridViewAdapter(context);
        Btn_lang_Ch = (Button) view.findViewById(R.id.lng_ch);
        Btn_Settings = (Button) view.findViewById(R.id.button_settings);
        favoriteDuas = (Button) view.findViewById(R.id.btn_favorite_duas);
        GridMenu =(GridView) view.findViewById(R.id.gridView1);
        float scalefactor = getResources().getDisplayMetrics().density * 150;
        @SuppressWarnings("deprecation")
        int number = getActivity().getWindowManager().getDefaultDisplay().getWidth();
        int columns = (int) ((float) number / (float) scalefactor);
        GridMenu.setAdapter(ga);
        GridMenu.setNumColumns(columns);
    }
    else {
       // remove view from previously attached ViewGroup
       ViewGroup parent = (ViewGroup) view.getParent();
       parent.removeView(view);
    }    
    return view;
}