Question

I have Application that contains main Activity, Service and several Threads run on this Service. The Activity has 1 button ‘Start service‘ and other UI. When user press on button, the name of button changes to ‘Stop service‘, the program creates new Service that stores information about CPU usage and pastes stored information to TextVeiw with frequency every 1 second.

Lets say I stopped main Activity. The Service continues to run but there is no any Activity that Service can pass data over.

After 1 min. I launch main Activity again. First of all I want to see above mentioned button state (name) ‘Stop service‘ and I want to see the old service which continue to talk with my new Activity.

I don’t intend to use LocalBinder and bindService(...); method since my Service stays in my own Application.

Any solutions?

Answer 1

Here is an extensive code example.

On start, Activity renders the instance to Application. Our Application will store instance of main Activity (or in other words Interface of Activity)

see GuiServiceBridgeItf gsb

snippets Application class

public class MyApplication extends Application{ 

    private static mYApplication mSingleton;

    public GuiServiceBridgeItf gsb = null;

 @Override
 public void onCreate() {
    super.onCreate();
    mSingleton = this;
 } 

 public mYApplication getApp(){
    return mSingleton;
 }
....
}

GuiServiceBridgeItf interface

public interface GuiServiceBridgeItf {
   public void onEventReceived(String str);

   /** Notify activity about service run */
   public void imHere();
....
}

Here is our Service that implements the same Interface GuiServiceBridgeItf.
MyService runs 2 Threads:

One Thread runs some logic (in our case notify Activity on CPU every second)

Second one notifies main Activity if Service runs (maybe better to provide this task to Activity to ask if Service runs)

public class MyService extends Service implements GuiServiceBridgeItf {

....

private RunnerThread runner = null;
private CheckAliveThread checkalive = null;

private MyApplication mMyApp = null;

public void onCreate() {
    super.onCreate();

    mMyApp  = (MyApplication)getApplicationContext();
}


public int onStartCommand(Intent intent, int flags, int startId) {

    GuiServiceBridgeItf gui2ServiceTalker = this;

    checkalive = new CheckAliveThread();
    checkalive.init(mMyApp);
    checkalive.start();


    runner = new RunnerThread(this.getApplicationContext(), gui2ServiceTalker);
    runner.start();

    ...

    return START_STICKY;
}

public void onDestroy() {   
    super.onDestroy();

    ...

    runner.doDestroy();     
    runner = null;  

    checkalive.doDestroy();
    checkalive = null;

    stopSelf();
}



private boolean isInstanceActive(){
    if(mMyApp.gsb == null){
        return false;
    }

    return true;
}


public void imHere() {}

public void onEventReceived(String str) {
    if(isInstanceActive()){
        mMyApp.gsb.onEventReceived(str);
    }
}

...

}

The main method here is: boolean isInstanceActive() that returns true or false on
Activity state. In other words if we down Activity, we unregister it’s instance from Application. Because onDestroy method in main Activity resets MyApplication.gsb.

In other hand when we relaunch new Activity, we register it to Application again, (see below)

public class LauncherUI extends Activity implements GuiServiceBridgeItf{

     ....
    @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

            // register Activity to Application    
            GuiServiceBridgeItf gts = this;     
    mApplicationApp = (MyApplication)mContext.getApplicationContext();
    mApplicationApp .gsb = gts;

            ....
   }

   ....

    @Override
protected void onDestroy() {
   super.onDestroy();
       ....
       // Unregister Activity to prevent to Service to talk with   
       mMyApplication.gsb = null;
}

}

the Service, by using his Thread, validates that Activity registered to Application and therefore continues to notify newborn Activity about CPU change. For now Activity can update button name to ‘Stop service‘ and do other stuff