Starting a runnable from a class causes a NetworkOnMainThreadException

Question

I am working on an Android project and I am having a problem.

If I implement the below code, it works fine.

new Thread(new Runnable() {

            @Override
            public void run() {
                try
                {
                    android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND);
                    DatagramSocket datagramSocket = new DatagramSocket(8000);

                    byte[] buffer = new byte[1024];
                    DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

                    while (true)
                    {
                        datagramSocket.receive(packet);

                        Log.v(TAG, new String(packet.getData(), 0, packet.getLength()));
                    }
                }
                catch (SocketException ex)
                {
                    Log.e(TAG, "Failed to bind socket. Exception: " + ex.toString());
                }
                catch (IOException ex)
                {
                    Log.e(TAG, "Failed to read socket data. Exception: "+ ex.toString());
                }
            }
        }).start();

What I am actually trying to do is create a class that implements a runnable but when I attempt to start it, I then get the exception for NetworkOnMainThreadException.

Below is my class

public class AddServerThread implements Runnable {

    private static final String TAG = "ADD SERVER THREAD";
    private boolean cancelThread = false;

    @Override
    public void run()
    {
        Log.d(TAG, "Listening for available servers");

        try
        {
            android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND);
            DatagramSocket datagramSocket = new DatagramSocket(8000);

            byte[] buffer = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

            while (!cancelThread)
            {
                datagramSocket.receive(packet);

                Log.v(TAG, new String(packet.getData(), 0, packet.getLength()));
            }
        }
        catch (SocketException ex)
        {
            Log.e(TAG, "Failed to bind socket. Exception: " + ex.toString());
        }
        catch (IOException ex)
        {
            Log.e(TAG, "Failed to read socket data. Exception: "+ ex.toString());
        }
    }

    public void cancelThread()
    {
        cancelThread = true;
    }
}

Below is how I am trying to start the thread

AddServerThread addServerThread = new AddServerThread();
        addServerThread.run();

I know what this exception means, what I don't understand is why it works on the first method, but when I use the class implementing Runnable I then get the exception.

Thanks for any help you can provide

When you call `run`, it executes `run`. When you call `start`, it starts a new `Thread` and executes `run` in that thread. So simply saying, make `AddServerThread extends Thread` and call `start`. — Yaroslav Mytkalyk, Jun 16 '14 at 21:42

score 0 · Accepted Answer · answered Jun 16 '14 at 21:41

0

Calling run on a runnable does not start a new thread. You need to pass it as a paramter to a thread.

Thread thread = new Thread(yourRunnable); thread.start();

answered Jun 16 '14 at 21:41

user184994

17,791
1
46
52

Starting a runnable from a class causes a NetworkOnMainThreadException

1 Answers1