· android

Learning Android: Getting a service to communicate with an activity

In the app I’m working on I created a service which runs in the background away from the main UI thread consuming the Twitter streaming API using twitter4j.

It looks like this:

public class TweetService extends IntentService {
    String consumerKey = "TwitterConsumerKey";
    String consumerSecret = "TwitterConsumerSecret";

    public TweetService() {
        super("Tweet Service");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        AccessToken accessToken = createAccessToken();

        StatusListener listener = new UserStreamListener() {
           // override a whole load of methods - removed for brevity

            public void onStatus(Status status) {
                String theTweet = status.getText();
                if (status.getText().contains("http://")) {
                    // do something with the tweet
                }

            }
        };
        ConfigurationBuilder configurationBuilder = new ConfigurationBuilder();
        configurationBuilder.setOAuthConsumerKey(consumerKey);
        configurationBuilder.setOAuthConsumerSecret(consumerSecret);

        TwitterStream twitterStream = new TwitterStreamFactory(configurationBuilder.build()).getInstance(accessToken);
        twitterStream.addListener(listener);
        twitterStream.user();
    }
}

That gets called from MyActivity like so:

public class MyActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        ...
        super.onCreate(savedInstanceState);
        Intent intent = new Intent(this, TweetService.class);
        startService(intent);
    }
}

I wanted to be able to inform the UI each time there was a tweet which contained a link in it so that the link could be displayed on the UI.

I found a post on StackOverflow which suggested that one way to do this would be to raise a broadcast message which could then be listened to by a BroadcastReceiver in the activity.

It is possible for any other apps to listen to the broadcast message as well if they wanted to but in this case the information isn’t very important so I think it’s fine to take this approach.

I first had to change the service to look like this:

public class TweetTask {
    public static final String NEW_TWEET = "tweet_task.new_tweet";
}

public class TweetService extends IntentService {
    String consumerKey = "TwitterConsumerKey";
    String consumerSecret = "TwitterConsumerSecret";

    public TweetService() {
        super("Tweet Service");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        AccessToken accessToken = createAccessToken();

        StatusListener listener = new UserStreamListener() {
           // override a whole load of methods - removed for brevity

            public void onStatus(Status status) {
                String theTweet = status.getText();
                if (status.getText().contains("http://")) {
                    Intent tweetMessage = new Intent(TweetTask.NEW_TWEET);
                    tweetMessage.putExtra(android.content.Intent.EXTRA_TEXT, document);
                    sendBroadcast(tweetMessage);
                }

            }
        };
        ConfigurationBuilder configurationBuilder = new ConfigurationBuilder();
        configurationBuilder.setOAuthConsumerKey(consumerKey);
        configurationBuilder.setOAuthConsumerSecret(consumerSecret);

        TwitterStream twitterStream = new TwitterStreamFactory(configurationBuilder.build()).getInstance(accessToken);
        twitterStream.addListener(listener);
        twitterStream.user();
    }
}

I then had to define the following code in MyActivity:

public class MyActivity extends Activity {
    protected void onResume() {
        super.onResume();
        if (dataUpdateReceiver == null) dataUpdateReceiver = new DataUpdateReceiver(textExtractionService);
        IntentFilter intentFilter = new IntentFilter(TweetTask.NEW_TWEET);
        registerReceiver(dataUpdateReceiver, intentFilter);
    }

    protected void onPause() {
        super.onPause();
        if (dataUpdateReceiver != null) unregisterReceiver(dataUpdateReceiver);
    }

    private class DataUpdateReceiver extends BroadcastReceiver {
        private CachedTextExtractionService textExtractionService;

        public DataUpdateReceiver(CachedTextExtractionService textExtractionService) {
            this.textExtractionService = textExtractionService;
        }

        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(TweetTask.NEW_TWEET)) {
                // do something with the tweet
            }

        }
    }
}

Now whenever there’s a tweet with a link in it my BroadcastReceiver gets notified and I can do whatever I want with the tweet.

This seems like a reasonably simple solution to the problem so I’d be interested to know if there are any other drawbacks other than the one I identified above.

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