I trying a hand at ListViews and my current experiment is aimed at
displaying some data in a ListView. The data to be displayed in each
row is simple: an image and some text. The images come from a remote
server and the textual data is hardcoded.
I have a class that downloads images using AsyncTask and caches the
list of images fetched as SoftReferences in a LinkedHashMap. I am also
passing a reference of the view to this class, so when the image
download/cache read is complete the class will set appropriate Bitmap
in the view.
Following is my code:
//class BasicAdapter extends ArrayAdapter<RowData>
...
static class ViewHolder{
TextView text;
ImageView icon;
}
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
ViewHolder holder;
if(convertView == null){
convertView =
mInflater.inflate(R.layout.listview_row,null);
holder = new ViewHolder();
holder.text = (TextView)
convertView.findViewById(R.id.row_txt);
holder.icon = (ImageView)
convertView.findViewById(R.id.row_img);
convertView.setTag(holder);
}
else{
holder = (ViewHolder) convertView.getTag();
}
holder.text.setText(mDataSet.get(position).getMText());
//set default icon
holder.icon.setImageResource(R.drawable.icon);
// set the actual image from the cache
String imageUrl = mDataSet.get(position).getMUrl();
WriteThroughCache.getImage(holder.icon, imageUrl);
return convertView;
}
// My helper class that manages cache and image Download
public class WriteThroughCache{
static LinkedHashMap<String,SoftReference<Bitmap>> imageCache =
new LinkedHashMap<String,SoftReference<Bitmap>>();
public static void getImage(ImageView icon, String imageUrl){
if(imageCache.containsKey(imageUrl)){
Bitmap image = imageCache.get(imageUrl).get();
if(image != null){
icon.setImageBitmap(image);
return;
}
}
new LoadImageInBackground().execute(new
Object[]{icon,imageUrl});
}
static class LoadImageInBackground extends AsyncTask<Object, Void,
Bitmap>{
ImageView mIcon = null;
String mUrl = null;
@Override
protected Bitmap doInBackground(Object... params) {
mIcon = (ImageView)params[0];
mUrl = (String) params[1];
Bitmap image = BitmapFactory.decodeStream
(GetMethodExecutor.getResponseStream(mUrl));
return image;
}
@Override
protected void onPostExecute(Bitmap result) {
super.onPostExecute(result);
mIcon.setImageBitmap(result);
imageCache.put(mUrl, new SoftReference<Bitmap>(result));
}
}
}
Problem: The applications seems to work just fine. However, when I
touch scroll the screen sometimes, the rows display the default image
and "Loading.." text. These are never refreshed.
But if I fling the listview, everything works normal then.
I am not sure of what I am missing here, please guide.
Thanks.
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