Android如何保存状态数组列表

Question

我正在制作一个 3 片段页面应用程序，在第一个片段上，它从 http 加载 json，但是当我转到 fragment3 并返回到 fragment1 时，它消失并从 http 再次加载。如何正确设置片段中的保存/恢复状态。

片段1代码：

    public class Fragment1 extends Fragment  {
 private ArrayList<FeedItem> feedList = null;
    private ProgressBar progressbar = null;
    private ListView feedListView = null;



  @Override  
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {  
      View rootView = inflater.inflate(R.layout.activity_post_list, container, false);

      progressbar = (ProgressBar)rootView.findViewById(R.id.progressBar);
      String url = "";
      new DownloadFilesTask().execute(url);
    return rootView;


  } 


  public void updateList() {
      feedListView= (ListView)getActivity().findViewById(R.id.custom_list);

      feedListView.setVisibility(View.VISIBLE);
      if (progressbar.isShown()) {
          progressbar.setVisibility(View.GONE); 
      }


      feedListView.setAdapter(new CustomListAdapter(getActivity(), feedList));
      feedListView.setOnItemClickListener(new OnItemClickListener() {



              @Override
              public void onItemClick(AdapterView<?> a, View v, int position, long id) {
                      Object o = feedListView.getItemAtPosition(position);
                      FeedItem newsData = (FeedItem) o;


                      Intent intent = new Intent(getActivity(), FeedDetailsActivity.class);
                      intent.putExtra("feed", newsData);
                      startActivity(intent);
              }
      });
        }

       public class DownloadFilesTask extends AsyncTask<String, Integer, Void> {

      @Override
      protected void onProgressUpdate(Integer... values) {
      }

      @Override
      protected void onPostExecute(Void result) {
              if (null != feedList) {
                      updateList();
              }
      }

      @Override
      protected Void doInBackground(String... params) {
              String url = params[0];

              // getting JSON string from URL
              JSONObject json = getJSONFromUrl(url);

              //parsing json data
              parseJson(json);
              return null;
      }
        }


       public JSONObject getJSONFromUrl(String url) {
      InputStream is = null;
      JSONObject jObj = null;
      String json = null;

      // Making HTTP request
      try {
              // defaultHttpClient
              DefaultHttpClient httpClient = new DefaultHttpClient();
              HttpPost httpPost = new HttpPost(url);

              HttpResponse httpResponse = httpClient.execute(httpPost);
              HttpEntity httpEntity = httpResponse.getEntity();
              is = httpEntity.getContent();

              BufferedReader reader = new BufferedReader(new InputStreamReader(
                              is, "iso-8859-1"), 8);
              StringBuilder sb = new StringBuilder();
              String line = null;
              while ((line = reader.readLine()) != null) {
                      sb.append(line + "\n");
              }
              is.close();
              json = sb.toString();
      } catch (UnsupportedEncodingException e) {
              e.printStackTrace();
      } catch (ClientProtocolException e) {
              e.printStackTrace();
      } catch (IOException e) {
              e.printStackTrace();
      }

      try {
              jObj = new JSONObject(json);
       } catch (JSONException e) {
              Log.e("JSON Parser", "Error parsing data " + e.toString());
       }

             // return JSON String
           return jObj;

          }

             public void parseJson(JSONObject json) {
            try {

              // parsing json object
              if (json.getString("status").equalsIgnoreCase("ok")) {
                      JSONArray posts = json.getJSONArray("posts");


                      feedList = new ArrayList<FeedItem>();

                      for (int i = 0; i < posts.length(); i++) {
                              JSONObject post = (JSONObject) posts.getJSONObject(i);
                              FeedItem item = new FeedItem();
                              item.setTitle(post.getString("title"));
                              item.setDate(post.getString("description"));
                              item.setId(post.getString("id"));
                              item.setUrl(post.getString("url"));
                              item.setContent(post.getString("description"));
                              item.setInfoz(post.getString("description"));
                              JSONArray attachments = post.getJSONArray("attachments");

                              if (null != attachments && attachments.length() > 0) {
                                      JSONObject attachment = attachments.getJSONObject(0);
                                      if (attachment != null)
                                              item.setAttachmentUrl(attachment.getString("url"));
                              }

                              feedList.add(item); 

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

Answer 1

这很简单：您可以覆盖方法onSaveInstanceState(bundle outState) 并将您想要的任何状态保存到outState。然后，在onCreateView() 中，您可以从对象savedInstanceState 中读取状态（如果有的话 - 它可能并且在首次启动时将为空），