如何从Android中的JSON在BaseAdapter中加载图像

Question

我创建了一个包含TextView，ImageView和Button的自定义列表。现在我试图从JSON URL显示图像，但是当我运行我的代码时，我收到一个NullPointerException。我不知道为什么我得到这个错误，因为TextView和Button正在显示它们各自的信息。

以下是BaseAdapter的代码：

public class SearchAdapter extends BaseAdapter { 

    Context context; 
    LayoutInflater inflater; 
    View vw; 
    ArrayList<String> unameList = new ArrayList<String>(); 
    ArrayList<String> statusList = new ArrayList<String>(); 
    ArrayList<String> uidList = new ArrayList<String>(); 
    ArrayList<String> picList = new ArrayList<String>(); 
    String id, message, url; 
    boolean status; 
    ConnectionStatus cs; 

    public SearchAdapter(Context context, LayoutInflater inflater, ArrayList<String> list1, ArrayList<String> list2, 
      ArrayList<String> list3, ArrayList<String> list4, String id) { 
     // TODO Auto-generated constructor stub 
     this.context = context; 
     this.inflater = inflater; 
     unameList.clear(); 
     statusList.clear(); 
     uidList.clear(); 
     picList.clear(); 
     unameList = list1; 
     statusList = list2; 
     uidList = list3; 
     picList = list4; 
     Log.v("srch", String.valueOf(picList)); 
     this.id = id; 
    } 

    public int getCount() { 
     // TODO Auto-generated method stub 
     return unameList.size(); 
    } 

    public Object getItem(int position) { 
     // TODO Auto-generated method stub 
     return position; 
    } 

    public long getItemId(int position) { 
     // TODO Auto-generated method stub 
     return 0; 
    } 
    private class ViewHolder { 
     ImageView img; 
     TextView tv; 
     Button btn; 
    } 
    public View getView(final int position, View convertView, ViewGroup parent) { 
     // TODO Auto-generated method stub 
     final ViewHolder holder; 
     if(convertView == null) 
     { 
      convertView = inflater.inflate(R.layout.list_items, null); 
      holder = new ViewHolder(); 
      holder.img = (ImageView)convertView.findViewById(R.id.imageView1); 
      holder.tv = (TextView)convertView.findViewById(R.id.textView1); 
      holder.btn = (Button)convertView.findViewById(R.id.button1); 
     } 
     else 
     { 
      holder = (ViewHolder)convertView.getTag(); 
     } 
     if(picList.get(position).startsWith("http:")) 
     { 
      try 
      { 
       URL url = new URL(picList.get(position)); 
       Log.v("url", url.toString()); 
       URLConnection conn = url.openConnection(); 
       conn.connect(); 
       InputStream is = conn.getInputStream(); 
       BufferedInputStream bis = new BufferedInputStream(is); 
       Bitmap bm = BitmapFactory.decodeStream(bis); 
       holder.img.setImageBitmap(bm); 
       bis.close(); 
       is.close(); 
      } 
      catch (IOException e) 
      { 
       e.printStackTrace(); 
       Log.e("Exception",e.getMessage()); 
      } 
     } 
     holder.tv.setText(unameList.get(position)); 
     if(statusList.get(position).contains("1")) 
     { 
      holder.btn.setText("listening"); 
     } 
     else 
     { 
      holder.btn.setText("listen"); 
     } 
     return convertView; 
    } 
} 

的logcat：

09-26 14:13:34.294: E/AndroidRuntime(1376): FATAL EXCEPTION: main 
09-26 14:13:34.294: E/AndroidRuntime(1376): java.lang.NullPointerException 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at com.pnf.flutterr.SearchAdapter.getView(SearchAdapter.java:105) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.AbsListView.obtainView(AbsListView.java:1315) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.ListView.makeAndAddView(ListView.java:1727) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.ListView.fillDown(ListView.java:652) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.ListView.fillFromTop(ListView.java:709) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.ListView.layoutChildren(ListView.java:1580) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.AbsListView.onLayout(AbsListView.java:1147) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.view.View.layout(View.java:7035) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.RelativeLayout.onLayout(RelativeLayout.java:909) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.view.View.layout(View.java:7035) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.FrameLayout.onLayout(FrameLayout.java:333) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.view.View.layout(View.java:7035) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1249) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1125) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.LinearLayout.onLayout(LinearLayout.java:1042) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.view.View.layout(View.java:7035) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.widget.FrameLayout.onLayout(FrameLayout.java:333) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.view.View.layout(View.java:7035) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.view.ViewRoot.performTraversals(ViewRoot.java:1045) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1727) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.os.Handler.dispatchMessage(Handler.java:99) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.os.Looper.loop(Looper.java:123) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at android.app.ActivityThread.main(ActivityThread.java:4627) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at java.lang.reflect.Method.invokeNative(Native Method) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at java.lang.reflect.Method.invoke(Method.java:521) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
09-26 14:13:34.294: E/AndroidRuntime(1376):  at dalvik.system.NativeStart.main(Native Method) 

相反，如果picList.get(position)你可以试试这个链接：

http://abhishekpnf.my3gb.com /test/uploads/180px-Lamborghini_Logo.svg.png

请帮我在寻找解决办法..

在此先感谢..

Answer 1

你知道什么导致空指针？在代码中进行下载的观点还是什么？

Answer 2

有一件事，你没有在convertView中设置标签，以便设置持有者对象。

编辑

final ViewHolder holder; 
    if(convertView == null) 
    { 
     convertView = inflater.inflate(R.layout.list_items, null); 
     holder = new ViewHolder(); 
     holder.img = (ImageView)convertView.findViewById(R.id.imageView1); 
     holder.tv = (TextView)convertView.findViewById(R.id.textView1); 
     holder.btn = (Button)convertView.findViewById(R.id.button1); 

     convertView.setTag(holder); // missing write this statement in if block at the end 
    } 
    else{ 
     ........ 

检查这一点，如果你得到同样的错误后，然后就在这里评论的//错误在该行更新您的问题