Interaction between IntentService and Activity - A

In my application I am using an IntentService to download a file from a cloud. And showing the progress in NotificationManager. I need to show the status (Downloading/Completed or Failed) in the Activity which stared the IntentService too.

My problem is once I closed the app and open it back, I want to get the status of downloading from IntentService.

Which is the best way to do this?

回答1:

You can let your Activity bind to your Service, by calling bindService() in your Activity. As per the documentation:

A service is "bound" when an application component binds to it by calling bindService(). A bound service offers a client-server interface that allows components to interact with the service, send requests, get results, and even do so across processes with interprocess communication (IPC). A bound service runs only as long as another application component is bound to it. Multiple components can bind to the service at once, but when all of them unbind, the service is destroyed.

Also:

You should create a bound service when you want to interact with the service from activities and other components in your application or to expose some of your application's functionality to other applications, through interprocess communication (IPC).

The documentation provides a fully functional example of this. Below is taken from the provided link.

Service class:

public class LocalService extends Service {
    // Binder given to clients
    private final IBinder mBinder = new LocalBinder();
    // Random number generator
    private final Random mGenerator = new Random();

    /**
     * Class used for the client Binder.  Because we know this service always
     * runs in the same process as its clients, we don't need to deal with IPC.
     */
    public class LocalBinder extends Binder {
        LocalService getService() {
            // Return this instance of LocalService so clients can call public methods
            return LocalService.this;
        }
    }

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    /** method for clients */
    public int getRandomNumber() {
      return mGenerator.nextInt(100);
    }
}

Activity class:

public class BindingActivity extends Activity {
    LocalService mService;
    boolean mBound = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    @Override
    protected void onStart() {
        super.onStart();
        // Bind to LocalService
        Intent intent = new Intent(this, LocalService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
    }

    @Override
    protected void onStop() {
        super.onStop();
        // Unbind from the service
        if (mBound) {
            unbindService(mConnection);
            mBound = false;
        }
    }

    /** Called when a button is clicked (the button in the layout file attaches to
      * this method with the android:onClick attribute) */
    public void onButtonClick(View v) {
        if (mBound) {
            // Call a method from the LocalService.
            // However, if this call were something that might hang, then this request should
            // occur in a separate thread to avoid slowing down the activity performance.
            int num = mService.getRandomNumber();
            Toast.makeText(this, "number: " + num, Toast.LENGTH_SHORT).show();
        }
    }

    /** Defines callbacks for service binding, passed to bindService() */
    private ServiceConnection mConnection = new ServiceConnection() {

        @Override
        public void onServiceConnected(ComponentName className,
                IBinder service) {
            // We've bound to LocalService, cast the IBinder and get LocalService instance
            LocalBinder binder = (LocalBinder) service;
            mService = binder.getService();
            mBound = true;
        }

        @Override
        public void onServiceDisconnected(ComponentName arg0) {
            mBound = false;
        }
    };
}

In your Service, you can define public methods that your Activity can call, such as polling for your download progress. Please refer to the documentation for explanation in detail.

回答2:

There are couple of ways to have communication connection between Service and Activity. I would suggest these 2

First, you can use the great library Otto. With Otto, you can also have @Produce annotated method. With this method you will return the latest information about the download. When you @Subscribe in your Activity you will get the latest info immediately. https://github.com/square/otto
If you are using Android built-in DownloadManager it returns the updates and results with a Broadcast, you can register to that Broadcast both in your Service and Activity. This way you will be able to update both of them. I suggest you to use DownloadManager, it is awesome. http://developer.android.com/reference/android/app/DownloadManager.html