How to use this.Dispose() from a Thread (Not main thread)

Question

How can I dispose a WinForm from a Non-Main Thread?

I have several threads running that are checked for .IsAlive from within another thread in a loop. Then I try to dispose them after they all die but it is not working as I envisaged, how do I dispose correctly?

Answer 1

If you need to interact with WinForms from non-UI thread you can use Invoke method. Next example create a form, shows it and then call dispose on it

public class DisposeFormDemo
{
    private class MyForm : Form
    {
        public MyForm() => Text = $"Main thread id = {Thread.CurrentThread.ManagedThreadId}";
    }

    public delegate void MyDelegate(Form form);

    public static void Main()
    {
        var form = new MyForm();

        Task.Run(async () => await Task.Delay(3000).ContinueWith(_ =>
        {
            MessageBox.Show($"Task thread id = {Thread.CurrentThread.ManagedThreadId}");

            var myDelegate = new MyDelegate(f =>
            {
                MessageBox.Show($"Current thread id = {Thread.CurrentThread.ManagedThreadId}");
                f.Dispose();
            });
            form.Invoke(myDelegate, form);
        }));

        form.ShowDialog();
    }
}

As you can see delegate will be executed on UI thread