My sample project source code in GitHub

Permissions

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

Open socket

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fun open(port: Int): Boolean {
    mPort = port
    try {
        mSocket = DatagramSocket(port)
        mSocket?.broadcast = true
        mSocket?.reuseAddress = true
        return true
    } catch (e: Exception) {
        e.printStackTrace()
    }
    return false
}

Close socket

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fun close(): Boolean {
    if (mSocket != null && mSocket?.isClosed?.not() as Boolean) {
        mSocket?.close()
    }
    return true
}

Send

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fun sendPacket(buffer: ByteArray): Boolean {
    try {
        val packet = DatagramPacket(buffer, buffer.size)
        packet.address = InetAddress.getByName("255.255.255.255")
        packet.port = mPort
        mSocket?.send(packet)
        return true
    } catch (e: Exception) {
        e.printStackTrace()
    }
    return false
}

Receive

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fun recvPacket(buffer: ByteArray): Boolean {
    val packet = DatagramPacket(buffer, buffer.size)
    try {
        mSocket?.receive(packet)
        println("recv packet ${packet.address} ${packet.data}")
        return true
    } catch (e: Exception) {
        e.printStackTrace()
    }
    return false
}

Reference

Android DatagramSocket Doc