在后退按鈕上獲取Android片段的先前狀態

Question

在一個Android應用程序中，我有多個片段，在片段之一（片段A）中，我使用布爾變量在按鈕單擊的GridView中切換兩組圖像。 GridView項目點擊導致第二個片段（片段B）。 在按下片段B上的“返回”按鈕時，片段A內的網格視圖將加載默認的圖像集，而不是在進入下一個片段片段B之前的設置圖像。

請指導我如何恢復上一組圖像而不是默認的圖像集？

在MainActivity中，我在BackPressed上實現了這樣的：

@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

你應該在片段的onCreate方法中調用setRetainInstance(true) ，或者在onSaveInstanceState和onRetainInstanceState保存和加載適當的值

編輯：我通常做這樣的事情：

@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;
}