android - 当我按下后退按钮时，如何阻止 GridView 再次加载？

Question

我用两个 fragment 创建了一个 Android 应用程序，MainFragment --> WebviewFragment。 MainFragment 是 GridView，它从 Json 链接中获取 Grid Item。当我通过按后退按钮从 WebviewFragment 导航回 MainFragment 时，Gridview 再次获取数据。有解决办法吗？

主要 fragment

public class MainFragment extends Fragment {


    // Log tag

    private static final String TAG = MainActivity.class.getSimpleName();

    // Movies json url

    private static final String url = "http://api....";
    private ProgressDialog pDialog;
    private List<Movie> movieList;
    private GridView gridView;
    private TextView scrollingtext;
    private AppController appController;





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

        movieList  = new ArrayList<Movie>();

        View view = inflater.inflate(R.layout.main_fragment, container, false);
        scrollingtext = (TextView) view.findViewById(R.id.scroll_annouc);
        scrollingtext.setSelected(true);
        gridView = (GridView) view.findViewById(R.id.Grid_view);
        final CustomListAdapter adapter = new CustomListAdapter(getActivity(), movieList);
        gridView.setAdapter(adapter);



            gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {



                    Bundle bundle = new Bundle();
                    bundle.putString("LINK","http://www.kalerkantho.com/");

                    Fragment newFragment = new WebviewFragment();
                    FragmentTransaction transaction = getFragmentManager().beginTransaction();
                    newFragment.setArguments(bundle);

                    transaction.replace(R.id.main_fragment_container, newFragment);
                    transaction.addToBackStack(null);
                    transaction.commit();


                }
            });


        pDialog = new ProgressDialog(getActivity());
        // Showing progress dialog before making http request
        pDialog.setMessage(" Loading ...");
        pDialog.show();

        // Creating volley request obj
        JsonArrayRequest movieReq = new JsonArrayRequest(url, new Response.Listener<JSONArray>() {
            @Override
            public void onResponse(JSONArray response) {
                Log.d(TAG, response.toString());
                hidePDialog();

                // Parsing json
                for (int i = 0; i < response.length(); i++) {
                    try {

                        JSONObject obj = response.getJSONObject(i);
                        Movie movie = new Movie();
                        movie.setTitle(obj.getString("title"));
                        movie.setThumbnailUrl(obj.getString("image"));


                        // adding movie to movies array
                        movieList.add(movie);

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }

                }

                // notifying list adapter about data changes
                // so that it renders the list view with updated data
               adapter.notifyDataSetChanged();
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                VolleyLog.d(TAG, "Error: " + error.getMessage());
                hidePDialog();

            }
        });



        // Adding request to request queue
        appController.getInstance().addToRequestQueue(movieReq);

        return view;
    }



    @Override
    public void onDestroy() {
        super.onDestroy();
        hidePDialog();
    }

    private void hidePDialog() {
        if (pDialog != null) {
            pDialog.dismiss();
            pDialog = null;
        }
    }

网页 View fragment

public class WebviewFragment extends Fragment {


    WebView webView;
    String newslink;

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

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

        newslink = getArguments().getString("LINK");

        webView = (WebView) view.findViewById(R.id.webView);
        webView.loadUrl(newslink);
        webView.getSettings().setJavaScriptEnabled(true);


        return view;
    }
}


     }

Answer 1

您可以使用 SharedPreferences 来保留您是否已加载数据的标志，然后在 fragment 之间切换时检查此标志。

如果您的标志处于 Activity 状态，您还应该将数据保存在 SharedPreferences 中，或者维护一个内部数据库并加载它，而不是再次转换您的 JSON。