Using CWAC’s EndlessAdapter with a custom adapter

In one of my projects, the app has the potential to display a very, and I mean very, long list. To minimize the loading time of the app, I limit the number of items initially included in the list and then add to it as the user scrolls down.

For this purpose, Mark Murphy’s EndlessAdapter works wonders. I was trying to make it work with a CursorAdapter though, but due to time constraints, I was not able to continue with my experiment.

And then I found out that some of the items in my list are HTML-formatted. Huh. So I have to have a custom adapter to override getView(). I patterned my code on the demo included in the EndlessAdapter project and I was at a loss. Maybe it’s because I just came from a vacation and my mind refuses to work. Hmmm.

To cut a long and arduous journey short, I was able to figure it out. Here’s a sample activity that displays a list of countries from an array. To illustrate using a custom adapter, I add the list item number when setting the item text.

I will discuss the pertinent parts of the code in detail.

private void init() {
    LIST_SIZE = COUNTRIES.length;
    for (int i=0; i<=BATCH_SIZE; i++){
        countriesSub.add(COUNTRIES[i]);
    }
    
    setLastOffset(BATCH_SIZE);
    displayList(countriesSub);
}

In this part of the code, I get the first 10 items in the list as the initial contents of the list. Of course, our current list is small and is peanuts for ListView. This is just to illustrate my point. In my app, I initially load 2,000 items. I also make sure to remember where I am in my source list. In my case, it is the offset in the original array. This might also be a row in the DB, or the ID in an RSS feed.

The ArrayList countriesSub holds the items that are currently in my list. As the user goes through the list, this array will grow.

To display my list, I set an instance of DemoAdapter as my list adapter. DemoAdapter inherits from EndlessAdapter and in its constructor, I give it an instance of my custom ArrayAdapter.

@Override
public View getView(int position,View convertView,ViewGroup parent){
        ViewHolder holder;

        if(convertView == null) {
            LayoutInflater inflater = (LayoutInflater)EndlessCustom.this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(android.R.layout.simple_list_item_1,null);
            holder = new ViewHolder();
            holder.word = (TextView)convertView.findViewById(android.R.id.text1);
            convertView.setTag(holder);
        } else {
            holder=(ViewHolder)convertView.getTag();
        }

        holder.word.setText(String.valueOf(position+1)+". "+countriesSub.get(position));
        return convertView;
        }

The important part in my custom ArrayAdapter is the getView() method. In this method, I tell the adapter to not simply display the .toString() value of the item, but to add a number before it.

Notice that I use the ViewHolder pattern as illustrated in the Android Developers site.

DemoAdapter() {
    super(new CustomArrayAdapter(EndlessCustom.this, android.R.layout.simple_list_item_1, android.R.id.text1, countriesSub));
    
    rotate = new RotateAnimation(0f, 360f, 
        Animation.RELATIVE_TO_SELF, 0.5f, 
        Animation.RELATIVE_TO_SELF, 0.5f);
    rotate.setDuration(600);
    rotate.setRepeatMode(Animation.RESTART);
    rotate.setRepeatCount(Animation.INFINITE);
}

So now we come to the EndlessAdapter part. In the constructor, I pass into it an instance of my custom ArrayAdapter, indicating the source of the list, the layout for each row, and the TextView ID from the layout. I also instantiated the animation that will be used while the list is loading the additional items.

@Override
protected boolean cacheInBackground() {
    tempList.clear();
    int lastOffset = getLastOffset();
    if (lastOffset < LIST_SIZE) {
        int limit = lastOffset + BATCH_SIZE;
        for(int i=(lastOffset+1); (i<=limit && i<LIST_SIZE); i++){
            tempList.add(COUNTRIES[i]);
        } 
        
        setLastOffset(limit);
        
        if (limit < LIST_SIZE) {
            return true;
        } else {
            return false;
        }
    } else  {
        return false;
    }
}

We have to override cacheInBackground() for EndlessAdapter to work. Here we do the heavy lifting like querying the server, reading from the DB, etc. Here, I load the next 10 items from the original list and put them in a temporary ArrayList. I also check whether I have loaded all the data, and if so, tell the EndlessAdapter to not show the extra row at the bottom. I do this by returning false from the method.

@Override
protected void appendCachedData() {
    @SuppressWarnings("unchecked")
    ArrayAdapter<String> arrAdapterNew = (ArrayAdapter<String>)getWrappedAdapter();
    
    int listLen = tempList.size();
    for(int i=0; i<listLen; i++){
        arrAdapterNew.add(tempList.get(i));
    }
}

Finally, I add the newly retrieved rows to my current list. And that’s it.

The complete Java file for this activity follows:

If you know of a more efficient way to do this, please do not hesitate to let me know! :)