Question

I have this windows form, timer1 is enabled and it’s interval is set to 2000 ms.
why the form shows a message box every 2 second? I mean when the first time timer tick called the UI thread will wait until the OK button pressed, so if I don’t push the button so there should not another message box appear. but it appears! why?

I know that timer works on it’s own thread, and the timer invokes the timer_tick function on it’s intervals, the question is how another messagebox is shown when UI thread is blocked on mbox.show()?

  public partial class Form1 : Form
  {
    public Form1()
    {
      InitializeComponent();
    }

    private void timer1_Tick(object sender, EventArgs e)
    {
      MessageBox.Show("test");
    }
  }

Answer 1

This is because you used MessageBox. It is a modal dialog that pumps a message loop. So all the normal Windows notifications are still delivered. Like paint events. The only thing it blocks is user input notifications, mouse and keyboard. But not a timer message. The Form.ShowDialog() method works this way as well.

You will have to disable the timer yourself.