Technical sharing on recent launched home widget feature

With recent launched of JStock Android, I manage to deliver home widget feature (finally). It took much longer time than I initial estimation. 8 weeks! (I work on it part-time)

Developing home widget is harder than I thought. There're 2 reasons for that.

No direct access to UI components

Developer doesn't have direct access to UI components of home widget. All UI manipulation, like setting text, is done through service. Service is only able to help developer to "set" UI's attributes. When developer wants to "get" UI's attributes, he can't! The only way is

• When setting an attribute of an UI, like setting text for a TextView, save the attribute value in persistence storage. For instance, SharedPreferences, SQLite, ...
• To get an attribute of an UI, read from previous stored value in SharedPreferences, SQLite, ...

No easy way to store current state of home widget

To fetch the latest stock price, and show it in ListView, here's what my first attempt looks like :-

1st Wrong Attempt - Doesn't use user thread and store data in static variables

public class JStockAppWidgetProvider extends AppWidgetProvider {

  public static final Map<Integer, Stock> stocksMap = new java.util.concurrent.ConcurrentHashMap<Integer, Stock>();

  @Override

  public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {

    for (int appWidgetId : appWidgetIds) {

      List<Stock> stocks = getStocks(appWidgetId);      

      stocksMap.put(appWidgetId, stocks);

      appWidgetManager.notifyAppWidgetViewDataChanged(appWidgetId, android.R.id.list);

    }

  }

}

// For ListView updating

public class AppWidgetRemoteViewsService extends RemoteViewsService {

  @Override

  public void onDataSetChanged() {

    this.stocks = JStockAppWidgetProvider.stocksMap.get(appWidgetId);

  }

}

There're 2 problem with such approach.

• getStocks is a time consuming operation. It should be done in user thread.
• Android OS might destroy AppWidgetProvider anytime. Hence, RemoteViewsService might get a null value.

2nd Attempt - Still not optimized

public class JStockAppWidgetProvider extends AppWidgetProvider {

  private static ExecutorService executor = Executors.newFixedThreadPool(1);

  @Override

  public void onUpdate(Context context, final AppWidgetManager appWidgetManager, 

    final int[] appWidgetIds) 

  {

    Runnable runnable = new Runnable() {

      @Override

      public void run() {

        for (int appWidgetId : appWidgetIds) {

          List<Stock> stocks = getStocks(appWidgetId);      

          storeStocksInSQLite(appWidgetId, stocks);

          appWidgetManager.notifyAppWidgetViewDataChanged(appWidgetId, android.R.id.list);

      }

    };

    executor.execute(runnable);

  }

}

// For ListView updating

public class AppWidgetRemoteViewsService extends RemoteViewsService {

  @Override

  public void onDataSetChanged() {

    this.stocks = readStocksFromSQLite(appWidgetId);

  }

}

This solution is not optimized yet. As, having to perform DB read access for every onDataSetChanged doesn't sound good to me. (Consume more battery, slower, ...) I modify the above code slightly, to reduce number of DB read access.

3rd Attempt - Optimized solution

public class JStockAppWidgetProvider extends AppWidgetProvider {

  public static final Map<Integer, Stock> stocksMap = new java.util.concurrent.ConcurrentHashMap<Integer, Stock>();

  private static ExecutorService executor = Executors.newFixedThreadPool(1);

  @Override

  public void onUpdate(Context context, final AppWidgetManager appWidgetManager, 

    final int[] appWidgetIds) 

  {

    Runnable runnable = new Runnable() {

      @Override

      public void run() {

        for (int appWidgetId : appWidgetIds) {

          List<Stock> stocks = getStocks(appWidgetId);      

          storeStocksInSQLite(appWidgetId, stocks);

          stocksMap.put(appWidgetId, stocks);

          appWidgetManager.notifyAppWidgetViewDataChanged(appWidgetId, android.R.id.list);

      }

    };

    executor.execute(runnable);

  }

}

// For ListView updating

public class AppWidgetRemoteViewsService extends RemoteViewsService {

  @Override

  public void onDataSetChanged() {

    this.stocks = JStockAppWidgetProvider.stocksMap.get(appWidgetId);
    // Is JStockAppWidgetProvider destroyed?

    if (this.stocks == null) {

      this.stocks = readStocksFromSQLite(appWidgetId);

    }

  }

}

This is what I had learnt during home widget development process. If you find out any mistake in my finding, feel free to let me know through

Thank you very much :)