Android- Loading Contacts with ViewHolder and AsyncTask- Thumbnail issue

问题

I am creating a custom contact app.. I use a ArrayAdapter with ViewHolder design pattern for optimization...Since it took a lot of time to load the thumbnail pics, I use AsyncTask class for loading images, for the first set of contacts in my screen, the pics are loading well but when I scroll down, the same set of pictures are being re-cycled at random for other contacts...I have searched this forumn and found a few solutions but none worked for me. I shall put my code below.. Someone pls tell me what is wrong in the code instead of marking it as duplicate qn...

public class CustomList extends ArrayAdapter<String>{

    private final Activity context;
    private final ArrayList<String> displayName,demoteValue,emergency;
    ArrayList<Long> contactId;

    public CustomList(Activity context,ArrayList<Long> contactId,ArrayList<String> displayName,ArrayList<String> demoteValue ,
            ArrayList<String> emergency) {
        super(context, R.layout.list_single, displayName);
        this.context = context;
        this.displayName = displayName;
        this.demoteValue = demoteValue;
        this.emergency = emergency;
        this.contactId=contactId;

    }

    class MyViewHolder
    {
        public QuickContactBadge imageView;
        public TextView txtTitle;
        int position;

        MyViewHolder(View v){
            txtTitle = (TextView) v.findViewById(R.id.txt);
            imageView = (QuickContactBadge) v.findViewById(R.id.contactimageentry);
        }
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View rowView=convertView;
        MyViewHolder holder=null;

        if(rowView==null)
        {
             LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
             rowView = inflater.inflate(R.layout.list_single, parent, false);
             holder=new MyViewHolder(rowView);
             rowView.setTag(holder);

        }else{
            holder= (MyViewHolder) rowView.getTag();
        }

        holder.txtTitle.setText(displayName.get(position));
        holder.txtTitle.setPadding(5, 5, 5, 5);
        //Some BLA BLA BLA work.
        if(emergency.get(position).equals("1")){

            holder.txtTitle.setTextSize(TypedValue.COMPLEX_UNIT_SP,25);
            holder.imageView.getLayoutParams().width=getPixels(TypedValue.COMPLEX_UNIT_DIP,50);

}            
        //Get and set the photo-HERE LIES THE CALL TO THE PROBLEM
        holder.position = position;
        new LoadContactImage(getContext(),holder,position,contactId.get(position))
        .executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, null);       
        return rowView;
    }   
}

And here is the code for my Async Task that loads the images based on the ID which I have passed while calling it

public class LoadContactImage extends AsyncTask<Object, Void, Bitmap> {

private long Path;
private MyViewHolder mHolder;
private int mposition;
Context ctx;

public LoadContactImage(Context context,MyViewHolder holder,int position,Long id) {
    this.mHolder= holder;
    this.Path = id;
    this.mposition=position;
    this.ctx= context;
}

@Override
protected Bitmap doInBackground(Object... params) {
    Uri my_uri = getPhotoUri(Path);
    ContentResolver cr = ctx.getContentResolver();
    InputStream in = null;
    try {
        in = cr.openInputStream(my_uri);
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    Bitmap bitmap = BitmapFactory.decodeStream(in);
    return bitmap;
}

@Override
protected void onPostExecute(Bitmap result) {

    super.onPostExecute(result);
    if (result != null && mposition == mHolder.position) {
        //imv.setImageBitmap(result);
        mHolder.imageView.setImageBitmap(result);
    }
}   
}

回答1:

Figured it out...Now its working..Soln given by Simon Meyer in Comments is correct..I need to initialize the imageView to a bitmap in getView() before I could call Async Task..Here is the change in code

holder.position = position;

holder.imageView.setImageURI( Uri.parse("android.resource://com.vishnu.demotingprototype/drawable/ic_contact_picture"));

new LoadContactImage(getContext(),holder,position,contactId.get(position)).execute();

回答2:

i think your customclass is not find out the context of lader image class. Declare context in yorr activity first.all is going well rather than this....Its works fine

来源：https://stackoverflow.com/questions/20173132/android-loading-contacts-with-viewholder-and-asynctask-thumbnail-issue