How to get results from an IntentService back into an Activity?
android, android-intent
Solution
You should look at creating your own `ResultReceiver` subclass in your activity. `ResultReceiver` implements `Parcelable` so can be passed from your `Activity` to your `Service` as an extra on the `Intent`.
You'll need to do something like this:
Implement a subclass of `ResultReceiver` within your activity class. The key method to implement is `onReceiveResult()`. This method provides you a with `Bundle` of result data which can be used to pass whatever information you are retrieving in your `Service`. Simply unpack the data you need and use it to update your activity.
In your activity, create a new instance of your custom `ResultReceiver` and add it to the `Intent` you use to start your service.
In your `Service`'s `onStartCommand()` method, retrieve the `ResultReceiver` passed in on the `Intent` and store it in a local member variable.
Once your `Service` completes its work, have it call `send()` on the ResultReceiver passing whatever data you want to send back to the activity in a `Bundle`.
This is a pretty effective pattern and means you're not storing data in nasty static variables.
Problem
I am using an IntentService to handle network communications with a server via JSON. The JSON/server part is working fine, but I'm having trouble getting the results back where they are needed. The following code shows how I am starting the intent service from inside onClick(), and then having the service update a global variable to relay the results back to the main activity. ``` public class GXActivity extends Activity { private static final String TAG = "GXActivity"; @Override public void onCreate(Bundle savedInstanceState) { // === called when the activity is first created Log.i(TAG, "GXActivity Created"); super.onCreate(savedInstanceState); setContentView(R.layout.start); View.OnClickListener handler = new View.OnClickListener() { public void onClick(View v) { // === set up an application context to hold a global variable // === called user, to contain results from the intent service GXApp appState = ((GXApp) getApplicationContext()); User user = new User(-1); // initialize user id to -1 appState.setUser(user); // === next start an intent service to get JSON from the server; // === this service updates the user global variable with // === results from the JSON transaction Intent intent = new Intent(this, GXIntentService.class); startService(intent); // === check app context for results from intent service appState = ((GXApp) getApplicationContext()); if (appState.getUser().getId() != -1)... } } } } ``` The problem I'm having is that the intent service that parses the JSON doesn't get invoked until after onCreate() completes, so my code that's looking for the results is stuck looking at uninitialized results. What should I do differently so the intent service gets called before I check the results? Would it work if I pulled the click listener out of the onCreate() function? Is there a another/better to structure this code? Many thanks.