What's wrong with my cross-thread call in Windows Forms?

Question

I encounter a problem with a Windows Forms application.

A form must be displayed from another thread. So in the form class, I have the following code:

Answer 1

Try this one:

private delegate void DisplayDialogCallback();

public void DisplayDialog()
{
    if (this.InvokeRequired)
    {
        this.Invoke(new DisplayDialogCallback(DisplayDialog));
    }
    else
    {
        if (this.Handle != (IntPtr)0) // you can also use: this.IsHandleCreated
        {
            this.ShowDialog();

            if (this.CanFocus)
            {
                this.Focus();
            }
        }
        else
        {
            // Handle the error
        }
    }
}

Please note that InvokeRequired returns

true if the control's Handle was created on a different thread than the calling thread (indicating that you must make calls to the control through an invoke method); otherwise, false.

and therefore, if the control has not been created, the return value will be false!