Question

I will be very grateful if someone can help me one this 🙂

I have a Custom Adapter (extending ArrayAdapter), and on the objects it displays (movieDatas), there is a property that vary with time (downloadProgress)

Since I use this adapter in multiple places, I wondered wether it is possible for my CustomAdapter to listen to every movieDatas.downloadProgress property, and then update itself ? Thus, not using ArrayAdapter.notifyDataSetChanged from the activity, but the adapter would take the decision to update by itself.

Previously, I used a Timer on every Activity that called myListView.invalidate() every 5 seconds, but I wondered if the adapter could handle the changes by itself ?

Thank you very much for your help, I begin in android development.

Answer 1

I don’t know how you’re doing it, but it sounds like you could totally use a callback to implement it.

1) Create an interface like this:

public interface OnDownloadProgressChangeListener{
    public void onProgress(int progress);
}

2) Add this to your MovieData object:

// We use an ArrayList because you could need to listen to more than one event. If you are totally sure you won't need more than one listener, just change this with one listener 
private ArrayList<OnDownloadProgressChangeListener> listeners = new ArrayList<OnDownloadProgressChangeListener>();

public void addDownloadProgressChangeListener(OnDownloadProgressChangeListener listener){
    listeners.add(listener);
}

public void clearDownloadProgerssChangeListeners(){
    listeners.clear();
}

//Add any handlers you need for your listener array.


// ALWAYS use this method to change progress value.
public void modifyProgress(int howMuch){
     progress+=howMuch;
     for (OnDownloadProgressChangeListener listener : listeners)
          listener.onProgress(progress);
}

3) Override your custom adapter add method

@Override
public void add(final MovieData item){
    item.addDownloadProgressChangeListener(new OnDownloadProgressChangeListener(){
        public void onProgress(final int progress){
             // Add your logic here
             if (progress == 100){
                  item.update();
             }
        }
    });
    super.add(item);
}

4) Whenever an item gets modified, call notifyDataSetChanged() on your adapter. You can even add it after the super.add(item) line in the add implementation, but this is extremely inefficient if you’re going to add a lot of items: Add them first then notify the changes.