Android ListView適配器返回NullPointerException

Question

當試圖將圖像填充到持有人的ImageView中或當我嘗試將持有人圖像視圖設置爲onclick偵聽器時，該應用崩潰。它實際上崩潰，如果我試圖做什麼與持有人的imageview相關。

圖片URL不爲空，我查

的ImageView的存在，我查

適配器代碼（它的重要位）：

public class FeedAdapter extends BaseAdapter { 

    static private Activity activity; 
    private static LayoutInflater inflater = null; 
    ArrayList<ActivityTable> actList = new ArrayList<ActivityTable>(); 
    Holder holder; 

    public FeedAdapter(Activity a, ArrayList<ActivityTable> actList) { 
      activity = a; 
      inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
      this.actList = actList; 
    } 

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

      View vi = convertView; 
      final ActivityTable act = actList.get(position); 

      if (vi == null) { 
        vi = inflater.inflate(R.layout.feed_single_picture, parent, false); 
        holder = new Holder(); 
        holder.media = (ImageView) vi.findViewById(R.id.postphoto); 
        //can't set an image to it either. it crashes. 
      } 
      else { 
        holder = (Holder) vi.getTag(); 
      } 

      //This is where it crashes 
      holder.media.setOnClickListener(new View.OnClickListener() { 
         @Override 
         public void onClick(View v) { 

           //other on Click related Code 

         } 
      }); 
     return vi; 
    } 

    public static class Holder { 
      ImageView media; 
    } 
} 

爲什麼Holder的ImageView崩潰了嗎？我嘗試添加一個TextView，ImageButton等，所有這些都正常工作。只是這個特定的imageview崩潰。我究竟做錯了什麼？

編輯：崩潰日誌

FATAL EXCEPTION: main 
    Process: com.metalproject.metalprojectmobile, PID: 5737 
    java.lang.NullPointerException 
      at Adapter.FeedAdapter.getView(FeedAdapter.java:456) 
      at android.widget.AbsListView.obtainView(AbsListView.java:2689) 
      at android.widget.ListView.makeAndAddView(ListView.java:1801) 
      at android.widget.ListView.fillDown(ListView.java:697) 
      at android.widget.ListView.fillGap(ListView.java:661) 

以上線：456分 - > holder.media.setOnClickListener（新View.OnClickListener（）{

Answer 1

您應該修改代碼如下所示：

if (vi == null) { 
    vi = inflater.inflate(R.layout.feed_single_picture, parent, false); 
    holder = new Holder(); 
    holder.media = (ImageView) vi.findViewById(R.id.postphoto); 
} 

並且還將它們從外部代碼中移除if if

Answer 2

修復將是這樣的：

public View getView(int position, View convertView, ViewGroup parent) { 
    View vi = convertView; 
    final ActivityTable act = actList.get(position); 

    if (vi == null) { 
     vi = inflater.inflate(R.layout.feed_single_picture, parent, false); 
     holder = new Holder(); 
     vi.setTag(holder); 
    }else { 
     holder = (Holder) vi.getTag(); 
    } 

    holder.media.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
     } 
    }); 
    return vi; 
} 

static class Holder { 

    private ImageView media; 

    Holder(View view){ 
     this.media = (ImageView) view.findViewById(R.id.postphoto); 
    } 

}