與Asynctask和自定義適配器的ListFragment

我的問題是非常基本的，但我看不到解決方案。這是我在Android上的第三個項目。到目前爲止，我使用的是帶有在其中聲明的ListView的片段，onCreateView，其中我正在充氣我的ListView和onActivityCreated以初始化佈局。現在我想要做同樣的事情，但使用ListFragment。與Asynctask和自定義適配器的ListFragment

我用這個〔實施例作爲參考：http://developer.android.com/training/basics/fragments/creating.html

下面被修改，我用於片段與一個ListView代碼。我改變了這個與ListFragment一起工作，但沒有成功。有人可以幫我嗎？先謝謝你。

public class PlayersListFragment extends ListFragment { 
    OnPlayerSelectedListener mCallback; 

    // URL to make request 
    private static String URL = Utils.URL; 
    private static int userID; 
    ArrayList<HashMap<String, Object>> playersList; 
    ListView playerView; 
    private Dialog pDialog; 

    // The container Activity must implement this interface so the frag can 
    // deliver messages 
    public interface OnPlayerSelectedListener { 
     /** Called by HeadlinesFragment when a list item is selected */ 
     public void onPlayerSelected(int position); 
    } 

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

     // We need to use a different list item layout for devices older than 
     // Honeycomb 
     int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ? android.R.layout.simple_list_item_activated_1 
       : android.R.layout.simple_list_item_1; 

     // Create an array adapter for the list view, using the Ipsum headlines 
     // array 
     setRetainInstance(true); 
     new PlayersLoadTask().execute(); 
    } 


    @Override 
    public void onActivityCreated(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     initLayout(); 
    } 

    public boolean onOptionsItemSelected(MenuItem item) { 
     return false; 
    } 


    private void initLayout() {   
     if(getActivity().getIntent()!=null) { 
      userID = getActivity().getIntent().getIntExtra("id", 0); 
     } else { 
      return; 
     } 
     playerView = (ListView) getActivity().findViewById(R.id.list); 
     playersList = new ArrayList<HashMap<String, Object>>(); 
     int[] colors = {0, 0xFFFF0000, 0}; // red for the example 

    } 
    @Override 
    public void onStart() { 
     super.onStart(); 

     // When in two-pane layout, set the listview to highlight the selected 
     // list item 
     // (We do this during onStart because at the point the listview is 
     // available.) 
     if (getFragmentManager().findFragmentById(R.id.playerDetailFragment) != null) { 
      getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE); 
     } 
    } 


    @Override 
    public void onAttach(Activity activity) { 
     super.onAttach(activity); 

     // This makes sure that the container activity has implemented 
     // the callback interface. If not, it throws an exception. 
     try { 
      mCallback = (OnPlayerSelectedListener) activity; 
     } catch (ClassCastException e) { 
      throw new ClassCastException(activity.toString() 
        + " must implement OnPlayerSelectedListener"); 
     } 
    } 

    @Override 
    public void onListItemClick(ListView l, View v, int position, long id) { 
     // Notify the parent activity of selected item 
     mCallback.onPlayerSelected(position); 

     // Set the item as checked to be highlighted when in two-pane layout 
     getListView().setItemChecked(position, true); 
    } 

    class PlayersLoadTask extends AsyncTask<String, String, String> { 

     @Override 
     protected void onPreExecute() { 
      pDialog = ProgressDialog.show(getActivity(), "", 
        "Loading. Please wait...", true); 
     } 

     @Override 
     protected String doInBackground(String... params) { 
      try { 

       ArrayList<BasicNameValuePair> parameters = new ArrayList<BasicNameValuePair>(); 
       parameters.add(new BasicNameValuePair("request", "getPlayers")); 
       parameters.add(new BasicNameValuePair("clubid", Integer 
         .toString(userID))); 

       DefaultHttpClient httpClient = new DefaultHttpClient(); 
       HttpPost httpPost = new HttpPost(URL); 
       httpPost.setEntity(new UrlEncodedFormEntity(parameters, 
         ("ISO-8859-1"))); 
       HttpResponse httpResponse = httpClient.execute(httpPost); 
       HttpEntity httpEntity = httpResponse.getEntity(); 

       // if this is null the web service returned an empty page 
       if (httpEntity == null) // response is empty so exit out 
        return null; 

       String jsonString = EntityUtils.toString(httpEntity); 

       if (jsonString != null && jsonString.length() != 0) 
       { 
        JSONArray jsonArray = new JSONArray(jsonString); 
        for (int i = 0; i < jsonArray.length(); i++) { 
         HashMap<String, Object> map = new HashMap<String, Object>(); 
         JSONObject jsonObject = (JSONObject) jsonArray.get(i); 
         int id = jsonObject.getInt("id"); 
         String name = jsonObject.getString("name"); 

         map.put("id", id); 
         map.put("name", name); 
         playersList.add(map); 

        } 
       } 
      } catch (UnsupportedEncodingException e) { 
       e.printStackTrace(); 
      } catch (ClientProtocolException e) { 
       e.printStackTrace(); 
      } catch (IOException e) { 
       e.printStackTrace(); 
      } catch (JSONException e) { 
       e.printStackTrace(); 
      } catch (Exception e) { 
       Log.e("ERROR SOMEWHERE!!!! ", e.toString()); 
      } 
      return null; 

     } 

     @Override 
     protected void onPostExecute(String file_url) { 
      if (pDialog.isShowing()) 
       pDialog.dismiss(); 
      if (playersList.size() == 0) { 
       Toast.makeText(getActivity(), "No players in a list", 
         Toast.LENGTH_SHORT).show(); 
      } else { 
       playerView.setAdapter(new PlayerListAdapter(// <<== EXCEPTION HERE 
         getActivity(), R.id.player_list_id, 
         playersList)); 
      } 

     } 
    } 
}

和關閉過程從哪個點上這條線logcat的堆棧跟蹤：playerView.setAdapter(new PlayerListAdapter(

12-18 11:34:30.181: E/AndroidRuntime(16436): FATAL EXCEPTION: main 
12-18 11:34:30.181: E/AndroidRuntime(16436): java.lang.NullPointerException 
12-18 11:34:30.181: E/AndroidRuntime(16436): at com.statsports.statisticalandroid.PlayersListFragment$PlayersLoadTask.onPostExecute(PlayersListFragment.java:199) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at com.statsports.statisticalandroid.PlayersListFragment$PlayersLoadTask.onPostExecute(PlayersListFragment.java:1) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at android.os.AsyncTask.finish(AsyncTask.java:631) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at android.os.AsyncTask.access$600(AsyncTask.java:177) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at android.os.Handler.dispatchMessage(Handler.java:99) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at android.os.Looper.loop(Looper.java:137) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at android.app.ActivityThread.main(ActivityThread.java:5103) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at java.lang.reflect.Method.invokeNative(Native Method) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at java.lang.reflect.Method.invoke(Method.java:525) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
12-18 11:34:30.181: E/AndroidRuntime(16436): at dalvik.system.NativeStart.main(Native Method)

來源

2013-12-18 Jakubee

這就是我解決我的問題的方法。看來你必須在onCreate（）或onActivityCreated（）中包含setListAdapter（）。代碼以供將來參考：

public class PlayersListFragment extends ListFragment { 
OnPlayerSelectedListener mCallback; 

// URL to make request 
private static String URL = Utils.URL; 
private static int userID; 
ArrayList<HashMap<String, Object>> playersList; 
ListView playerView; 
private ProgressDialog pDialog; 

// The container Activity must implement this interface so the frag can 
// deliver messages 
public interface OnPlayerSelectedListener { 
    /** Called by HeadlinesFragment when a list item is selected */ 
    public void onPlayerSelected(int position); 
} 




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

    new PlayersLoadTask().execute(); 
    int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ? 
      android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1; 
    setListAdapter(new PlayerListAdapter(getActivity(), layout, playersList)); 

} 

public boolean onOptionsItemSelected(MenuItem item) { 
    return false; 
} 


private void initLayout() {   
    if(getActivity().getIntent()!=null) { 
     userID = getActivity().getIntent().getIntExtra("id", 0); 
    } else { 
     return; 
    } 
    playerView = getListView(); 
    playersList = new ArrayList<HashMap<String, Object>>(); 

} 
@Override 
public void onStart() { 
    super.onStart(); 

    // When in two-pane layout, set the listview to highlight the selected 
    // list item 
    // (We do this during onStart because at the point the listview is 
    // available.) 
    if (getFragmentManager().findFragmentById(R.id.playerDetailFragment) != null) { 
     playerView.setChoiceMode(ListView.CHOICE_MODE_SINGLE); 
    } 
} 


@Override 
public void onAttach(Activity activity) { 
    super.onAttach(activity); 

    // This makes sure that the container activity has implemented 
    // the callback interface. If not, it throws an exception. 
    try { 
     mCallback = (OnPlayerSelectedListener) activity; 
    } catch (ClassCastException e) { 
     throw new ClassCastException(activity.toString() 
       + " must implement OnPlayerSelectedListener"); 
    } 
} 

@Override 
public void onListItemClick(ListView l, View v, int position, long id) { 
    // Notify the parent activity of selected item 
    mCallback.onPlayerSelected(position); 

    // Set the item as checked to be highlighted when in two-pane layout 
    playerView.setItemChecked(position, true); 
} 

class PlayersLoadTask extends AsyncTask<String, String, String> { 

    @Override 
    protected void onPreExecute() { 
     pDialog = ProgressDialog.show(getActivity(), "", 
       "Loading. Please wait...", true); 
    } 

    @Override 
    protected String doInBackground(String... params) { 
     try { 

      ArrayList<BasicNameValuePair> parameters = new ArrayList<BasicNameValuePair>(); 
      parameters.add(new BasicNameValuePair("request", "getPlayers")); 
      parameters.add(new BasicNameValuePair("clubid", Integer 
        .toString(userID))); 

      DefaultHttpClient httpClient = new DefaultHttpClient(); 
      HttpPost httpPost = new HttpPost(URL); 
      httpPost.setEntity(new UrlEncodedFormEntity(parameters, 
        ("ISO-8859-1"))); 
      HttpResponse httpResponse = httpClient.execute(httpPost); 
      HttpEntity httpEntity = httpResponse.getEntity(); 

      // if this is null the web service returned an empty page 
      if (httpEntity == null) // response is empty so exit out 
       return null; 

      String jsonString = EntityUtils.toString(httpEntity); 

      if (jsonString != null && jsonString.length() != 0) 
      { 
       JSONArray jsonArray = new JSONArray(jsonString); 
       for (int i = 0; i < jsonArray.length(); i++) { 
        HashMap<String, Object> map = new HashMap<String, Object>(); 
        JSONObject jsonObject = (JSONObject) jsonArray.get(i); 
        int id = jsonObject.getInt("id"); 
        String name = jsonObject.getString("name"); 

        map.put("id", id); 
        map.put("name", name); 
        playersList.add(map); 

       } 
      } 
     } catch (UnsupportedEncodingException e) { 
      e.printStackTrace(); 
     } catch (ClientProtocolException e) { 
      e.printStackTrace(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } catch (Exception e) { 
      Log.e("ERROR SOMEWHERE!!!! ", e.toString()); 
     } 
     return null; 

    } 

    @Override 
    protected void onPostExecute(String file_url) { 
     if (pDialog.isShowing()) 
      pDialog.dismiss(); 
     if (playersList.size() == 0) { 
      Toast.makeText(getActivity(), "No players in a list", 
        Toast.LENGTH_SHORT).show(); 

     } else if(playerView != null) { 
      setListAdapter(new PlayerListAdapter(getActivity(), R.id.player_list_id, playersList)); 
      /*playerView.setAdapter(new PlayerListAdapter(
        getActivity(), R.id.player_list_id, 
        playersList));*/ 
     } 
    } 
}

來源

2013-12-20 14:44:20 Jakubee

在onActivtiyCreated調用中，你有以上的下方

playerView = (ListView) getActivity().findViewById(R.id.list);

是initLayout()造成什麼原因NullPointerException

因此改爲

playerView = getListView(); // since you extend ListFragment

來源

2013-12-18 11:42:53 Raghunandan

@Jakubee這意味着你在運行時生成列表視圖，而不是在XML文件 –

創建它運行的AsyncTask，並顯示進度條，但之後就死機秒，並指出對onPostExecute（），但是，方法之外的'}'之一。 – Jakubee

@Jakubee到stacktrace你的playerView爲null。需要重新運行並重新發布堆棧跟蹤 – Raghunandan

與Asynctask和自定義適配器的ListFragment

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