ViewHolder in ListView adapter not working

Question

I've been trying to make my ListView scroll smoother with ViewPager, but it keeps crashing. I've tried around 3 types of solution. The screen opens, the loading indicator shows but after a while (about 3-5 seconds) it crashes. To load images from URL do I use Universal-Image-Loader lib by nostra13. It all worked well without adding the ViewHolder.

My LogCat and getView + ViewHolder in Adapter class:

LogCat

    01-30 17:01:53.713: E/AndroidRuntime(12702): FATAL EXCEPTION: main
01-30 17:01:53.713: E/AndroidRuntime(12702): java.lang.NullPointerException
01-30 17:01:53.713: E/AndroidRuntime(12702):    at com.example.animalist.AnimalAdapter$1.onLoadingComplete(AnimalAdapter.java:123)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at com.nostra13.universalimageloader.core.DisplayBitmapTask.run(DisplayBitmapTask.java:74)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at android.os.Handler.handleCallback(Handler.java:587)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at android.os.Handler.dispatchMessage(Handler.java:92)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at android.os.Looper.loop(Looper.java:143)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at android.app.ActivityThread.main(ActivityThread.java:4263)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at java.lang.reflect.Method.invokeNative(Native Method)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at java.lang.reflect.Method.invoke(Method.java:507)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
01-30 17:01:53.713: E/AndroidRuntime(12702):    at dalvik.system.NativeStart.main(Native Method)
01-30 17:01:57.957: I/wpa_supplicant(15739): Reset vh_switch_counter due to receive LINKSPEED cmd

in AnimalAdapter.java - getView + ViewHolder

 static class ViewHolder{
        TextView animalView;
        TextView areaView;
        ImageView notfound;
        ImageView animalPic;
        ProgressBar indicator;
    }
    
    
    public View getView(int position, View convertView, ViewGroup parent){
        
        ViewHolder holder = null;
        
        
        
        if(convertView == null){
              LayoutInflater mLayoutInflater = LayoutInflater.from(mContext);
              convertView = mLayoutInflater.inflate(R.layout.animal_row_item, null);
              holder = new ViewHolder();
              
             holder.animalView = (TextView) convertView.findViewById(R.id.animal_text);
              holder.areaView = (TextView) convertView.findViewById(R.id.area_text);
            holder.notfound = (ImageView) convertView.findViewById(R.id.notfoundimg);
              holder.animalPic = (ImageView)convertView.findViewById(R.id.animal_pic);
              holder.indicator = (ProgressBar)convertView.findViewById(R.id.progress);
               convertView.setTag(holder);
          }
          
        else{
            holder = (ViewHolder) convertView.getTag();
                    
        }  
        
          final Animal animal = mAnimals.get(position);
          
          
          
          
          holder.notfound.setVisibility(View.INVISIBLE);
          holder.indicator.setVisibility(View.VISIBLE);
          holder.animalPic.setVisibility(View.INVISIBLE);
          
            //Setup a listener we can use to switch from the loading indicator to the Image once it's ready
            ImageLoadingListener listener = new ImageLoadingListener(){


                ViewHolder holder = null;
                @Override
                public void onLoadingStarted(String arg0, View arg1) {
                    // TODO Auto-generated method stub

                }

                @Override
                public void onLoadingCancelled(String arg0, View arg1) {
                    // TODO Auto-generated method stub

                }

                @Override
                public void onLoadingComplete(String arg0, View arg1, Bitmap arg2) {
                    holder.indicator.setVisibility(View.INVISIBLE);
                    holder.animalPic.setVisibility(View.VISIBLE);
                    holder.notfound.setVisibility(View.INVISIBLE);
                }

                @Override
                public void onLoadingFailed(String arg0, View view, FailReason arg2) {
                    holder.notfound.setVisibility(View.VISIBLE);
                    holder.indicator.setVisibility(View.INVISIBLE);
                    holder.animalPic.setVisibility(View.INVISIBLE);
                }

            };

            
            
          imageLoader.displayImage(animal.getImgUrl(), holder.animalPic,options, listener);
          holder.animalView.setText(animal.getAnimal());
          holder.areaView.setText(animal.getArea());
          
          
          
          
          
          convertView.setOnClickListener(new OnClickListener() {
              
                @Override
                public void onClick(View view) {
                    
                    Intent intent = new Intent(getContext(), MoreActivity.class);
                    
                    intent.putExtra("about", animal.getAbout());
                    intent.putExtra("animal", animal.getAnimal());
                    intent.putExtra("imgUrl", animal.getImgUrl());
                    getContext().startActivity(intent);
                }
          });
          
          return convertView;
      }

Do you have any idea, how to improve it?

Thanks in advance

Answer 1

I think your logic is not right, in your getView() method you test:

if (vi == null){

But there you should test whether:

if (convertView == null) {

Try changing it, should work this way.

---- EDIT ----

The way you initialize your ViewHolder seems ok to me, afterwards you assign each instance a View via findViewById(), which is ok - If you're getting a NullPointerException setting the visibility, that means that for some reason the findViewById() returned a null object - i.e., it didn't find an id with the name R.id.progress (probably there is no such element in your layout with that name).

---- EDIT ----

Here goes an example of my adapter's getView() method:

public static class vhItem {
  TextView maintext;
  TextView topictext; 
  ImageView mainimage;
  TextView users; 
}

@Override
public View getView(final int position, View convertView, final ViewGroup parent) {
  vhItem viewHolder;

  if (convertView == null) {
    final LayoutInflater inflater = ((Activity) context).getLayoutInflater();
    convertView = inflater.inflate(resourceId, parent, false);

    viewHolder = new vhItem();
    viewHolder.maintext = (TextView) convertView.findViewById(R.id.chanlist_chan);
    viewHolder.topictext = (TextView) convertView.findViewById(R.id.chanlist_topic);
    viewHolder.mainimage = (ImageView) convertView.findViewById(R.id.chanlist_featured);
    viewHolder.users = (TextView) convertView.findViewById(R.id.chanlist_usercount);

    // I've set a contextual menu for each row this way, but it's not required
    ((Activity) context).registerForContextMenu(convertView);
  }
  else
    viewHolder = (vhItem) convertView.getTag();

  viewHolder.maintext.setText((String) getItem(position));
  viewHolder.mainimage.setTag(getItem(position));
  viewHolder.mainimage.setOnClickListener(new View.OnClickListener() {
    public void onClick(final View v) {
      AlertDialog.Builder builder = new AlertDialog.Builder(context);
      ...
      dialog.show();
    }
  });

  return convertView; 
}

Answer 2

the fact the in the stacktrace you have

01-30 16:45:09.003: E/AndroidRuntime(12533):    at android.widget.ListView.measureHeightOfChildren(ListView.java:1264)
01-30 16:45:09.003: E/AndroidRuntime(12533):    at android.widget.ListView.onMeasure(ListView.java:1127)

suggests that the convertView you are returning is null.

About your second issue, your ViewHolder instance inside ImageLoadingListener is always null. You should take care to initialise it accordingly