implementing a callback in android with Activities

Question

I am developing an library for Android and have following scenario, I want a response back to MainActivity. How could I do it? I have tried with callbacks but could not as I could not create an object of Activity class by myself. is there any other way to achieve it? in AsyncTaskListener implementation I am doing some network operation. I could not use startActivityForResult as it's not according to my library specification.

public class MainActivity extends AppCompatActivity implements MyReceiver{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    MyServiceImpl b = new MyServiceImpl();
    String request = "123";
    b.request(this,request);
    }

    @Override
    public void completed(String result) {        
        Log.d("MainActivity","Result - "+result);
    }
}

public class MyServiceImpl{

   public void request(Activity appActivity,String req){
        Intent intent = new Intent(appActivity, ActivityB.class);
        appActivity.startActivity(intent);
   } 
}

public class ActivityB extends AppCompatActivity imnplements AsyncTaskListener{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // shows UI 
        // network operations
    }

   @Override
   public void taskFinish(String response) {
     //  my result comes here
     //  now  i want this result to propagated to MainActiviy
   }
}

Read this post, https://stackoverflow.com/questions/3398363/how-to-define-callbacks-in-android — Dhruv Patel, Nov 13 '17 at 10:40
you can use onActivityResult to get back the response from Activity B to Activity A — sree, Nov 13 '17 at 10:53

Sarthak Gandhi · Accepted Answer · 2022-05-26T12:53:01.480

5

I would do it like this :

Create an interface :

public interface MyReceiver {
  public void onReceive();
}

In you activity :

public class MyActivity implements MyReceiver{

public static MyReceiver myReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    setContentView(R.layout.activity_new_booking);        
    super.onCreate(savedInstanceState);
    myReceiver = this;
    }
    
    @Override
    protected void onDestroy() {
        myReceiver = null;
    }


    @Override
    public void onReceive(){
       //Implement your code here or send objects in the parameters
    }

}

To Call it just use this:

if(MyActivity.myReceiver!=null){
  MyActivity.myReceiver.onReceive();
}

No need to create activity instances.

In this case i would also suggest you to use startActivityForResult.

Hope this helps.

edited May 26 '22 at 12:53

answered Nov 13 '17 at 10:40

Sarthak Gandhi

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for me your MyActivity means my MainActivity or ActivityB ? – Shailesh Nov 13 '17 at 10:52
MainActivity. I just gave an example it can be any activity. – Sarthak Gandhi Nov 13 '17 at 10:52
Then from the ActivityB you call the function when needed. – Sarthak Gandhi Nov 13 '17 at 10:53
Can you please upvote the answer too. So that it is helpful for other people. – Sarthak Gandhi Nov 13 '17 at 11:52
This is wrong. You're leaking the activity by making MyReceiver static and accessing it from non activity classes. If this is what you want to do, you might as well create a static method inside the activity directly. – Rishabh Bhardwaj Mar 09 '22 at 20:55

score 2 · Answer 2 · answered Nov 13 '17 at 11:11

For this purpose I use Singleton approach.

class ActivityCommunication {
private static ActivityCommunication instance = null;
private MainCallback mainCallback = null;

private ActivityCommunication() {
}

public static ActivityCommunication getInstance() {
    if (instance == null) {
        instance = new ActivityCommunication();
    }
    return instance;
}

public void setMainCallBackListener(MainCallback mainCallback) {
    this.mainCallback = mainCallback;
}

public void sendDataToMainActivity(Data data) {
    if (mainCallback != null) {
        mainCallback.onMainCallBack(data);
    }
}

public interface MainCallback {
    void onMainCallBack(Data data);
}
}

On MainActivity set the listener

 ActivityCommunication.getInstance().setMainCallBackListener();

On from ActivityB, send the data when you need

 ActivityCommunication.getInstance().sendDataToMainActivity(myData);

Implemented onMainCallBack method will be then called.

score 0 · Answer 3 · answered Nov 13 '17 at 10:33

You can do one thing. Create an object of your library when activity starts and pass the reference of your activity to that object instantiation. And implement that interface call back to the activity. And internally in your library, you will have activity reference cast that to your interface callback and call interface method that will give you call back at your activity level.

implementing a callback in android with Activities

3 Answers3