Android MapActivity thread question

Question

How do I ensure code is or is not executed on the UI thread in an Android MapActivity project?

I am developing an Android map-based application, but I have experienced some stability issues and my research has led me to believe I need to ensure that screen updates are carried out on the UI thread.

My app has data coming in from a GPS listener (which I would like to configure as a separate thread) and a UDP listener (which is already a separate thread), and it has the usual set of android software life cycle methods, but I must be inexperienced or something, because I have no idea where to put code that updates the map overlays

(a) on the UI thread, (b) in a recurring manner.

I have no preference between a polling or an event-driven process (timer-based perhaps, or the arrival of incoming data), so suggestions of either type will be gratefully accepted.

Anyone got any ideas??

Thanks, R.

Answer 1

Read this post on painless threading, particularly the Activity.runOnUIThread

Answer 2

You can also look at this Handling Expensive Operations in UI Thread. In your case you can do the following:

public class MyActivity extends Activity {

[ . . . ]
// Need handler for callbacks to the UI thread
final Handler mHandler = new Handler();

// Create runnable for posting
final Runnable mUpdateResults = new Runnable() {
    public void run() {
        updateResultsInUi();
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //setup location listener 
    [ . . . ]
    startNonUIThread();
}

protected void startNonUIThread() {

    // Fire off a thread to do some work that we shouldn't do directly in the UI thread
    Thread t = new Thread() {
        public void run() {
           try{
            while(true){
               sleep(1000); 
               mHandler.post(mUpdateResults);
             }
           }catch(InterruptedException e){
            //blah blah
            }
        }
    };
    t.start();
}

private void updateResultsInUi() {

    // Back in the UI thread -- update UI elements based on data from locationlistener
    //get listener location
    //use the location to update the map 
    [ . . . ]
}

}

Answer 3

The android location service is a module that runs in the background so you do not need to seperate it in another thread.

However I would not recommend you to use java thread class or runnable interface at all, use async task instead which performs all the thread management for you. Have a look at the android developers blog, Painless Threading.

To update your UI thread on location updates you can use update handlers. Everytime there is GPS data avialable a message is transmitted to the update handler in you main ui thread.

E.g.

public void onLocationChanged(Location location) {
    location = this.lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
    try {
        this.mLongitude = location.getLongitude();
        this.mLatitude = location.getLatitude();    
        Message msg = Message.obtain();
        msg.what = UPDATE_LOCATION;
        this.SystemService.myViewUpdateHandler.sendMessage(msg);
    } catch (NullPointerException e) {
        Log.i("Null pointer exception " + mLongitude + "," + mLatitude, null);
    }
}   

And in your main activity class:

Handler myViewUpdateHandler = new Handler(){

        public void handleMessage(Message msg) {
                switch (msg.what) {
                case UPDATE_LOCATION:               
                //do something
               }
               super.handleMessage(msg);
        }
    };