在使用自定義列表的同時獲取NPE

Question

我有一個ListFragment，我想使用自定義佈局。佈局非常好，所有資源都在他們的地方。但我仍然得到空指針異常。

列表片段編碼：

public class InboxFragment extends ListFragment { 

protected List<ParseObject> mMessages; 

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

    return rootView; 
} 

@Override 
public void onResume() { 
    super.onResume(); 

    getActivity().setProgressBarIndeterminateVisibility(true); 

    ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(ParseConstants.CLASS_MESSAGES); 
    query.whereEqualTo(ParseConstants.KEY_RECIPIENT_IDS, ParseUser.getCurrentUser().getObjectId()); 
    query.addDescendingOrder(ParseConstants.KEY_CREATED_AT); 
    query.findInBackground(new FindCallback<ParseObject>() { 
     @Override 
     public void done(List<ParseObject> messages, ParseException e) { 
      getActivity().setProgressBarIndeterminateVisibility(false); 

      if (e == null) { 
       // We found messages! 
       mMessages = messages; 

       String[] usernames = new String[mMessages.size()]; 
       int i = 0; 
       for(ParseObject message : mMessages) { 
        usernames[i] = message.getString(ParseConstants.KEY_SENDER_NAME); 
        i++; 
       } 
       MessageAdapter adapter = new MessageAdapter(
         getListView().getContext(), 
         mMessages); 
       setListAdapter(adapter); 
      } 
     } 
    }); 
} 

@Override 
public void onListItemClick(ListView l, View v, int position, long id) { 
    super.onListItemClick(l, v, position, id); 

    ParseObject message = mMessages.get(position); 
    String messageType = message.getString(ParseConstants.KEY_FILE_TYPE); 
    ParseFile file = message.getParseFile(ParseConstants.KEY_FILE); 
    Uri fileUri = Uri.parse(file.getUrl()); 

    if (messageType.equals(ParseConstants.TYPE_IMAGE)) { 
     // view the image 
     Intent intent = new Intent(getActivity(), ViewImageActivity.class); 
     intent.setData(fileUri); 
     startActivity(intent); 
    } 
    else { 
     // view the video 
     Intent intent = new Intent(Intent.ACTION_VIEW, fileUri); 
     intent.setDataAndType(fileUri, "video/*"); 
     startActivity(intent); 
    } 
} 

}

我與該片段中所使用的適配器：

public class MessageAdapter extends ArrayAdapter<ParseObject> { 

protected Context mContext; 
protected List<ParseObject> mMessages; 

public MessageAdapter(Context context, List<ParseObject> messages) { 
    super(context, R.layout.message_item, messages); 
    mContext = context; 
    mMessages = messages; 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    ViewHolder holder; 

    if (convertView == null) { 
     convertView = LayoutInflater.from(mContext).inflate(R.layout.message_item, null); 
     holder = new ViewHolder(); 
     holder.iconImageView = (ImageView)convertView.findViewById(R.id.messageIcon); 
     holder.nameLabel = (TextView)convertView.findViewById(R.id.senderLabel); 
    } 
    else { 
     holder = (ViewHolder)convertView.getTag(); 
    } 

    ParseObject message = mMessages.get(position); 
    if (message.getString(ParseConstants.KEY_FILE_TYPE).equals(ParseConstants.TYPE_IMAGE)) { 
     holder.iconImageView.setImageResource(R.drawable.ic_action_picture); 
    } 
    else { 
     holder.iconImageView.setImageResource(R.drawable.ic_action_play_over_video); 
    } 
    holder.nameLabel.setText(message.getString(ParseConstants.KEY_SENDER_NAME)); 

    return convertView; 
} 

private static class ViewHolder { 
    ImageView iconImageView; 
    TextView nameLabel; 
} 

}

此處是LogCat : Image

圖像

的第45行是這一行：

holder.iconImageView.setImageResource(R.drawable.ic_action_picture); 

這裏是佈局的XML文件：

<ImageView 
    android:id="@+id/messageIcon" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentLeft="true" 
    android:layout_alignParentTop="true" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/message_list_item_vertical_margin" 
    android:paddingBottom="@dimen/message_list_item_vertical_margin" 
    android:src="@drawable/ic_action_picture" /> 

<TextView 
    android:id="@+id/senderLabel" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_centerVertical="true" 
    android:layout_toRightOf="@+id/messageIcon" 
    android:textAppearance="?android:attr/textAppearanceMedium" 
    android:paddingLeft="@dimen/activity_horizontal_margin" /> 

    </RelativeLayout> 

我的圖片在我的繪製文件夾，但我仍然得到這個錯誤。任何人都可以請建議，這個代碼有什麼問題。

Answer 1

缺少getView）主要的事情（這會導致holder=null

public View getView(int position, View convertView, ViewGroup parent) { 
    ViewHolder holder; 

    if (convertView == null) { 
     convertView = LayoutInflater.from(mContext).inflate(R.layout.message_item, null); 
     holder = new ViewHolder(); 
     holder.iconImageView = (ImageView)convertView.findViewById(R.id.messageIcon); 
     holder.nameLabel = (TextView)convertView.findViewById(R.id.senderLabel); 

     convertView.setTag(holder) // this line 
    } 
    else { 
     holder = (ViewHolder)convertView.getTag(); 
    } 

遵循@CommonsWare