Question

I have a bit troublesome with view caching in listview (a.k.a convertView)
so here is my code,

private class CurrencyAdapter extends ArrayAdapter<CurrencyModel> {
    Context ctx;
    int layoutResourceId;
    List<CurrencyModel> adapter_models = null;

    public CurrencyAdapter(Context ctx, int layoutResourceId,
            List<CurrencyModel> model) {
        super(ctx, layoutResourceId, model);
        this.ctx = ctx;
        this.layoutResourceId = layoutResourceId;
        adapter_models = model;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        Log.d(Constants.APP_TAG, "position: " + position);
        View row = convertView;
        CurrencyAdapterContainer holder = null;
        if (row == null) {
            Log.d(Constants.APP_TAG, "APP NULL");
            row = ((Activity) ctx).getLayoutInflater().inflate(
                    layoutResourceId, parent, false);
            holder = new CurrencyAdapterContainer();
            holder.textView = (TextView) row
                    .findViewById(R.id.currencies_txt);
            holder.imgView = (ImageView) row
                    .findViewById(R.id.currencies_flag_icon);
            row.setTag(holder);

        } else {
            Log.d(Constants.APP_TAG, "APP NOT NULL");
            holder = (CurrencyAdapterContainer) row.getTag();
        }

        CurrencyModel curr = getItem(position);

        if (curr.currency_value == null) {
            if (counter < MAX_COUNTER) {
                ++counter;
                CurrencyJsonDownloader cDownloader = new CurrencyJsonDownloader(
                        curr, holder.textView);  //download currency value in background, and set textview text if currency_value has been loaded in onpostExcecute (i'm using AsyncTask)
                String url = CURRENCY_URL.replace("<symbol>", curr.symbol);
                Log.d(Constants.APP_TAG, "Url currency: " + url);
                cDownloader.execute(url);
            }
            holder.textView.setText("");
        } else {
            holder.textView.setText(curr.currency_value);
        }
        holder.imgView.setImageResource(curr.drawableId);

        return row;
    }

    @Override
    public CurrencyModel getItem(int position) {
        // TODO Auto-generated method stub
        return adapter_models.get(position);
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return adapter_models.size();
    }
}

static class CurrencyAdapterContainer {
    ImageView imgView;
    TextView textView;
}

and here is the output in my logcat

position : 0
APP NULL

position : 1
APP NOT NULL

position : 2
APP NOT NULL

position : 3
APP NOT NULL

.
.
.

position : 10
APP NOT NULL

which make a disaster because it means that the textview being passed in the background job is the same textview and the the changed view is the same textview and the other textview will have blank view unless i scroll it of course which call again the getView() and everything is fine. But it’s a problem when starting the app, because just one textview that always changing its value.

so why is this happen? and is there any hack that i can do??
thanks before…

Answer 1

ListView item Views are recycled, so never hold a reference to a particular item view and expect it to represent same data after ListView has been scrolled.

Pass the data item to your worker task instead and let it update the data to it.

Updating:

• If your current item is off screen, It’ll be requested from adapter (
  when ListView scroll to it), and will show updated data.
• If that item is currently being displayed , call notifyDataSetChanged() on adapter, this will make ListView refresh its displayed items.