Setting Listview Row Images Asynchrourously in Android

public class AsyncImageSetter extends AsyncTask<Void, Void, Bitmap> {  
  
private ImageView img;  
private int image_resId;  
private Context c;  
private boolean cancel = false;  
private int sampleSize;  
  
  
public AsyncImageSetter(Context c, ImageView img, int image_ResId) {  
  
    this.img = img;  
    this.image_resId = image_ResId;  
    this.c = c;  
  
}  
  
public void cancel() {  
    cancel = true;  
}  
  
@Override  
protected void onPreExecute() {  
    /*--- we hide the Views from the user until the content is ready. This will prevent 
     * the user from seeing an image being "transformed" into the next one (as a result of 
     * View recycling) on slow devices.  
     */  
    //img.setVisibility(View.GONE);  
 super.onPreExecute();  
}  
  
@Override  
protected Bitmap doInBackground(Void... params) {  
  
    if (!cancel) {  
        try {  
            return decodeAndScale();  
        } catch (Exception e) {  
            e.printStackTrace();  
        }  
    }  
    return null;  
}  
  
@Override  
protected void onPostExecute(Bitmap result) {  
  
    //img.setVisibility(View.VISIBLE);  
 try {  
        img.setImageBitmap(result);  
    } catch (Exception e) {  
        /*--- show an error icon in case something went wrong ---*/  
 img.setImageResource(R.drawable.close);  
    }  
  
    super.onPostExecute(result);  
}  
  
private Bitmap decodeAndScale() {  
  
    final BitmapFactory.Options options = new BitmapFactory.Options();  
    options.inSampleSize = setSampleSize();  
  
    return BitmapFactory.decodeResource(c.getResources(), image_resId,  
            options);  
  
}  
  
private int setSampleSize() {  
  
    // TODO add multiple screens check  
/*--- modify this method to match your needs ---*/  
 if (getScreenWidth((Activity) c) >= 320) {  
        /*--- physical width >= 480px ---*/  
 sampleSize = 2;  
    }  
  
    return sampleSize;  
}  
    public static int getScreenWidth(Activity a) {  
  
        Display display = a.getWindowManager().getDefaultDisplay();  
        DisplayMetrics outMetrics = new DisplayMetrics();  
        display.getMetrics(outMetrics);  
  
        float density = a.getResources().getDisplayMetrics().density;  
        float dpWidth = outMetrics.widthPixels / density;  
  
        return (int) dpWidth;  
  
    }  
  
}  

cell.imageloader = new AsyncImageSetter(context, cell.doctorImage,  
        mImageResources[position]);