How to pass values from a Class to Activity - Android

You can use Callback for this purpose.

Define some interface like

public interface MyCustomInterface(){
    public void sendData(String str);
}

Now let your Activity implement this interface.

public class MyActivity implements MyCustomInterface {

@Override
public void sendData(String str){

Handler handler = new Handler(Looper.getMainLooper());
handler.post(new Runnable() {
  @Override
  public void run() {
    recived_message.setText(str);
  }
});
}
}

Now in UDPServer.java, write the following code

public class UDPServer {

private MyCustomInterface interface;

UDPServer(MyCustomInterface interface){
 this.interface = interface; 
}

}

Now whenever you have some data available lets say a string, you can send it like this

interface.sendData(str);

You have an A activity and B one, when you finish actions on B activity side you need it to effect A side when you come back.

1. Create an Instance Class and a method that u type u need, let's say;

   public interface SelectedBirthday {
   
       void onSelectedData(String date);
   }
   

2. Now we are on B side, Create an instance of your Interface Class

   private SelectedBirthday mCallback;
   

3. Override

   @Override
   public void onAttach(Activity activity) {
       super.onAttach(activity);
   
       try {
           mCallback = (SelectedBirthday) activity;
       } catch (ClassCastException e) {
           Log.d("MyDialog", "Activity doesn't implement the ISelectedData interface");
       }
   }
   

4. Now upload the value you needed

   String userBirth = (day + " " + month + " " + year);
   
   mCallback.onSelectedData(userBirth);
   

5. Ok let's go to A side

Implement our Interface Class

implements SelectedBirthday

it will warn you for its method and you implemented it

     @Override
        public void onSelectedData(String date) {
            if (!date.equals("")) {
                txt_poup_age.setText(date);
//now you are free to do what you want with the value you received automaticaly
            }
        }