Receive UDP Broadcast from PC on Android

NanYuanZhiGe — Wed, 01 Jan 2025 12:45:44 +0000

This article implements how to receive UDP broadcasts from a PC on your mobile phone.
Let's first complete the code implementation on the PC side., which is very simple.

private final ScheduledExecutorService askService= Executors.newSingleThreadScheduledExecutor();

public void runWaitConnectThead(){
        askService.scheduleAtFixedRate(this::sendAskMessage, 0, boardCastConfig.getWAIT_MS(), TimeUnit.MILLISECONDS);
    }
protected void sendAskMessage(){
        byte[] message = this.hostName.getBytes();
        try (DatagramSocket datagramSocket = new DatagramSocket()) {
            datagramSocket.setBroadcast(true);
            InetAddress boardcastAddr = InetAddress.getByName("255.255.255.255");
            DatagramPacket datagramPacket = new DatagramPacket(message, message.length, boardcastAddr, 1885);
            datagramSocket.send(datagramPacket);
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }

In the second code block above, askService will start immediatly(the second param) and will continue to exucute function "sendAskMessage()"， which boardcast UDP packet， every boardCastConfig.getWAIT_MS() milliseconds. In my code, it repeats every 5s.

Now, you have achieved 50% success.
Before writing our receiving code, we need add some permissions in AndroidMnifest.xml file or your application will not able to run.
Here are the permissions:

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
    <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />

Then let's create a service in MainActivity, and implement our receiving code in it. By the way, don't forget adding this service in AndroidManifest.xml file.

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Intent waitBoardCastService=new Intent(this, WaitBoardCastService.class);
        startService(waitBoardCastService);
    }
}

<service android:name=".on_wait.WaitBoardCastService"/>

Then we can finish our receiving code. It contains two part.
①create a new thread(I didn't show that in my code, but that's very important, you can't start your application if you left network operation in main thread)
②acquiring multicast lock(this step is extremely important, without this, you can't receive UDP packet)
③receiving UDP packet

WifiManager wifi =(WifiManager)getSystemService(MyApplication.WIFI_SERVICE);
WifiManager.MulticastLock lock = wifi.createMulticastLock("any_tag");
lock.acquire();
try {
    DatagramSocket socket = new DatagramSocket(1885);
    byte[] receiveData = new byte[1024];
    DatagramPacket receivePacket = new DatagramPacket(receiveData, 
    receiveData.length);
    Log.v("hello","waiting");
    socket.receive(receivePacket);
    String receiveMessage = new String(receivePacket.getData(), 0,receivePacket.getLength());
    Log.v("hello","received!");
    socket.close();
} catch (IOException e) {
    Toast.makeText(MyApplication.getContext(), "NetWork Error",Toast.LENGTH_LONG).show();
} finally {
    lock.release();
}

My results:

DEV Community: NanYuanZhiGe

Receive UDP Broadcast from PC on Android