How to pass values from a Class to Activity - Android

Question

I have a newbie question about Class/Task/Activity. I'm coming from C so I don't know if it's a good approach to do what I need.

I've created a class:

public class UDPServer {

    private MyDatagramReceiver myDatagramReceiver = null;

    private static int MAX_UDP_DATAGRAM_LEN = 1024;
    private static int UDP_SERVER_PORT = 5000;

    public void start() {
        myDatagramReceiver = new MyDatagramReceiver();
        myDatagramReceiver.start();
    }

    public void kill() {
        myDatagramReceiver.kill();
    }

    private class MyDatagramReceiver extends Thread {
        private boolean bKeepRunning = true;
        private String lastMessage = "";

        public void run() {
            String message;
            byte[] lmessage = new byte[MAX_UDP_DATAGRAM_LEN];
            DatagramPacket packet = new DatagramPacket(lmessage, lmessage.length);
            DatagramSocket socket = null;

            try
            {
                socket = new DatagramSocket(UDP_SERVER_PORT);

                while(bKeepRunning)
                {
                    socket.receive(packet);
                    message = new String(lmessage, 0, packet.getLength());
                    lastMessage = message;

                    //Here should call activity method

                });
                }

            }
            catch (Throwable e)
            {
                e.printStackTrace();
            }
            finally
            {
                if (socket != null)
                {
                    socket.close();
                }
            }
        }

        public void kill() {
            bKeepRunning = false;
        }
    }
}

Inside my Activity I've:

@Override
public void onResume() {
    super.onResume();

    mUDPServer = new UDPServer();
    mUDPServer.start();
}

@Override
public void onPause() {
    super.onPause();

    mUDPServer.kill();
}

Now, every time I received a packet I want that this thread/class pass received packet to an Activity method that elaborate(do some calculation or update some UI ecc..) this incoming data. But I can't figure how to do this, maybe my approach is not correct. I can place thread code inside Activity but it seems to make code less readable.

Suggestion how to do this?

@Anshul Jain CODE UPDATE:

    public class Main_activity extends Activity implements Interface_UDPServer{
    TextView recived_message;

    UDPServer mUDPServer;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        recived_message = (TextView)findViewById(R.id.recived_message);
    }

    @Override
    public void onResume() {
        super.onResume();

        mUDPServer = new UDPServer(this);
        mUDPServer.start();
    }

    @Override
    public void onPause() {
        super.onPause();

        mUDPServer.kill();
    }

    public void sendData(final String str){
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                recived_message.setText(str);
            }
        });
    }

}

XML file

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:layout_below="@+id/linearLayout"
        android:layout_alignLeft="@+id/linearLayout"
        android:layout_alignStart="@+id/linearLayout">
    <TextView
        android:id="@+id/recived_message"
        android:layout_width="200dp"
        android:layout_height="35dp"
        android:textColor="#444444"
        android:textSize="20dp" />
    </LinearLayout>
</RelativeLayout>

Answer 1

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);

Answer 2

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
            }
        }

Answer 3

In android 4 option to do this

• In android you can send data through Intent or Intent followed by Bundle.Like Intent i = new Intent(current_class.this, linked_class.class); i.putextra("Key", value);

And get the value(suppose string value) in another class like:

 String value = getIntent.getExtra("String key which you used when send value");

• option 2

  class A{

  public static String _utfValue = "";

  void sendValue(){ _utfValue = "some value"; } }

And fetch this value in your java class like:

String value = A._utfValue ;

• You can use SharedPreference to save the value and get it from other class.
• You can use a static method with some return value and fetch the method in your java class through class name.