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。我不知道为什么我收到此错误，因为TextView和Button正在显示各自的信息。
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;
}
}
logcat的：
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)您可以尝试此链接：
http://abhishekpnf.my3gb.com/test/uploads/180px-Lamborghini_Logo.svg.png
请帮助我找到解决方案..
先谢谢..
答案 0 :(得分：0)
你知道什么导致NullPointer？是代码中的视图还是其他东西在进行下载？
答案 1 :(得分：0)
有一件事你没有在convertView中设置标签来设置持有者对象。
<强>被修改
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{
........
如果你得到同样的错误，请在此之后检查，然后在该行注释为//错误更新你的问题