Question

I have read in many places that network connection in a j2me app should be done in a separate thread. Is this a necessity or a good to have?

I am asking this because I could not find anywhere written that this must be done in a separate thread. Also, when I wrote a simple app to fetch an image over a network and display it on screen (without using a thread) it did not work. When I changed the same to use a separate thread it worked. I am not sure whether it worked just because I changed it to a separate thread, as I had done many other changes to the code also.

Can someone please confirm?

Edit:
If running in a separate thread is not a necessity, can someone please tell me why the below simple piece of code does not work?

It comes to a stage where the emulator asks “Is it ok to connect to net”. Irrespective of whether I press an “yes” or a “no” the screen does not change.

public class Moo extends MIDlet {

    protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
        // TODO Auto-generated method stub

    }

    protected void pauseApp() {
    }

    protected void startApp() throws MIDletStateChangeException {
        Display display = Display.getDisplay(this);
        MyCanvas myCanvas = new MyCanvas();
        display.setCurrent(myCanvas);
        myCanvas.repaint();

    }

    class MyCanvas extends Canvas {

        protected void paint(Graphics graphics) {
            try {
                Image bgImage = Image.createImage(getWidth(), getHeight());

                HttpConnection httpConnection = (HttpConnection) Connector
                        .open("https://stackoverflow.com/content/img/so/logo.png");
                Image image = Image.createImage(httpConnection
                        .openInputStream());
                bgImage.getGraphics().drawImage(image, 0, 0, 0);
                httpConnection.close();

                graphics.drawImage(bgImage, 0, 0, 0);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }

}

Edit: I got my answer for the code here.

Edit: I spawned off a separate question of this here.

Answer 1

The problem is that you are trying to do work within the thread that is responsible for running the UI. If you do not use a separate thread, then that UI thread is waiting while you do your work and can’t process any of your other UI updates! so yes you really should not do any significant work in event handlers since you need to return control quickly there.