Prevent duplicate MDI children forms

Question

Is there a way to prevent the opening of a certain form within an MDI container if that said form is already opened?

Answer 1

AFAIK there is no standard way. You'll have to implement it yourself. I'd do it this way:

class TheForm: Form
{
    private static TheForm Instance;

    private TheForm() // Constructor is private
    {
    }

    public static Show(Form mdiParent)
    {
        if ( Instance == null )
        {
            // Create new form, assign it to Instance
        }
        else
            Instance.Activate(); // Not sure about this line, find the appropriate equivalent yourself.
    }

    protected override OnFormClose(EventArgs e)
    {
        Instance = null;
        base.OnFormClose(e);
    }
}

If thread safety is of concern, add the appropriate locks.