即使应用未运行，用户也如何接收通知

Question

So I am trying to make an app so that when a row in a SQL database changes, the user receives a notification even though the app is not currently running. I'm pretty sure this is possible because Facebook can send mobile notifications when the app isn't running, but I'm not sure how to go about this.

Answer 1

You need to use Service which runs in background. From within a service you can start a notification. Its not clear that which 'notification' are you talking about? If you are talking about notification as in Google Cloud Messaging notification , then you need to go a different way. But, then also you would be using GCMIntentService which extends Service class.

You want to send a notification when when a row in a SQL database changes . Is that row changing on the server side? I am assuming yes because first you were talking about Android database, then you would have mentioned SQLite instead of SQL. Secondly you gave example of Facebook. So, if the answer to my question is yes, then using GCM push services you can send a Push Message to the user. Then when user receives the message, you can show a notification with the proper data. In the onReceive method of GCMIntentService , you will receive the content in an Intent. There you can extract the message and create a notification. See here for more.

Answer 2

You will need to register a content observer to get notified of the changes.

To use the ContentObserver you have to take two steps:

• Implement a subclass of ContentObserver
• Register your content observer to listen for changes
• Notify change from the content provider

--

class DbObserver extends ContentObserver {      
   public DbObserver(Handler handler) {
      super(handler);           
   }

   @Override
   public void onChange(boolean selfChange) {
      this.onChange(selfChange, null);
      // start the notification
   }        
}

Register your content observer to listen for the changes:

getContentResolver().
      registerContentObserver(
            SOME_URI, 
            true, 
            yourObserver);

Now can call notifyChange after updating your db.

notifyChange(Uri uri, ContentObserver observer)

A quick example of using content observer is https://gist.github.com/JBirdVegas/3874450

Answer 3

You can use Service in android

A service by default runs in the same process in the main thread as the application.

Therefore you need to use asynchronous processing in the service to perform resource intensive tasks in the background. A common used pattern for a service implementation is to create and run a new Thread in the service to perform the processing in the background and then to terminate the service once it has finished the processing.

Each Service has a specific job, and it will run continuously even if you switch between different Activities, or to a different application altogether.

To start a service use the following:

Intent i= new Intent(context, ServiceClass.class);
i.putExtra("KEY1", "Value to be used by the service");
context.startService(i); 

A simple example for a service class:

public class ServiceClass extends Service {
      @Override
      public int onStartCommand(Intent intent, int flags, int startId) {
        return Service.START_NOT_STICKY;
      }
      @Override
      public IBinder onBind(Intent intent) {
        return null;
      }
    }