How to update ListView from completely unrelated class

Question

I've read through a lot of questions on how to update a ListView. They all pretty much say adapter.notifyDataSetChanged() (if in a seperate thread with runOnUiThread).

My problem starts a bit earlier: How do I even get the Adapter I need or for that matter an Activity to call runOnUiThread?

Here is a very simplified version of my current code:

I have a class for the Data, which can be updated from anywhere at any time. The update method needs to start a new Thread, which is why I can't simply wait for a return value.

class Data {
private static double[] data = new double[7]

public static void update(final Context context) {

    new Thread(new Runnable() {
        @Override
        public void run() {
              //do lots of complicated stuff
        }
    }).start();
}

public double[] getData {
    return data;
}

I have an Activity (not the main Activity) that, among other stuff, contains the ListView

public class ListViewActivity extends ActionBarActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_ListView);
    ListView listView = (ListView) findViewById(R.id.MyListView);
    listView.setAdapter(new CustomListViewAdapter(this));
}

I then use a custom Adapter to set up the ListView how I want it.

class CustomListViewAdapter extends BaseAdapter {

private final LayoutInflater layoutInflater;

public CustomListViewAdapter(Context context) {
    layoutInflater = LayoutInflater.from(context);
}

@Override
public View getView(int position, View view, ViewGroup parent) {
    ViewHolder viewHolder = new ViewHolder();
    if (view == null) {
        view = layoutInflater.inflate(R.layout.listView_row_layout, parent, false);
        viewHolder.value = (TextView) view.findViewById(R.id.listViewDataTextField);
        view.setTag(viewHolder);
    } else {
        viewHolder = (ViewHolder) view.getTag();
    }
    double data = Data.getData()[position];
    viewHolder.value.setText(data+"");

    return view;
}
private class ViewHolder {
    TextView value;
}

Now I want to update the ListView with as soon as the Thread in the update() method has finished getting the new data. Getting the data can take several seconds, so it's impossible to predict, what activity will be active by that time. If my ListViewActivity is active, I want the ListView to change to the new data immediately.

So how do I update that ListView, from a different class, which is not an Activity, inside another thread? I don't suppose putting the adapter in a static field is a good idea, since that ListViewActivity is probably created and destroyed all the time? But what other options do I have?

Answer 1

extendIt looks like your major problem can be formulated shortly as "How do I even get the Adapter", so I'll try to address that. Let us try to use an old good Java singleton to solve the problem. The idea is to create a global config and pre-create adapters for all views that you need to update:

    public class GlobalConfig {

        private static GlobalConfig config = null;
        private CustomBaseAdapterOne adapter1 = null;
        private CustomBaseAdapterTwo adapter2 = null;
        public GlobalConfig getAdapterOne() {return adapter1;}
        public GlobalConfig getAdapterTwo() {return adapter2;}

        public static synchronized GlobalConfig getInstance() {
            if (config == null) {
                config = new GlobalConfig();
                config.adapter1 = new CustomBaseAdapterOne();
                config.adapter2 = new CustomBaseAdapterTwo();
            }
            return config;
        }
    }

Your ListViewActivity will need to extend DataSetObserver class and register an observer when it starts. You CustomListAdapter would need to register the observer when it starts and it will also need to be able to get initialized with init params (Context in your case) through a function (e.g. setContext), not through a constructor, so in your ListViewActivity you'll need to do something like below:

GlobalConfig cfg = GlobalConfig.getInstance();
CustomerAdapterOne ad = cfg.getAdapterOne();
ad.setContext(this);
ad.registerDataSetObserver(this);

From a separate thread that needs to update the ListView, you'll run:

GlobalConfig cfg = GlobalConfig.getInstance();
try {
    cfg.getAdapterOne().notifyDataSetChanged();
}
catch{... }

I think, it's a good idea to have try/catch here because I don't know what will happen if ListView has already died at the time when you need to notify.

To summarize: you'll need to pre-create one adapter for each view that needs to be updated and make it globally available for everyone who needs it.

Answer 2

Define a callback interface. Make your update method take an instance of this callback as an argument and call back to it when updating has finished.

public interface UpdateCallback {
    public void onUpdateFinished();
}

public void update(final Context context, final UpdateCallback callback) {

    new Thread(new Runnable() {
        @Override 
        public void run() { 
            // do lots of complicated stuff
            callback.onUpdateFinished();
        } 
    }).start();
}

Then in your Activity you can notify that the adapter data has changed:

Data.update(this, new UpdateCallback() {
    public void onUpdateFinished() {
        adapter.notifyDatasetChanged();
    }
});