How do you display a custom UserControl as a dialog?

namespace System.Window.Form
{
    public static class Ext
    {
        public static DialogResult ShowDialog(this UserControl @this, string title)
        {
            Window wind = new Window() { Title = title, Content = @this };
            return wind.ShowDialog();
        }
    }
}

The use of it maybe as simple as UserControlInstance.ShowDialog(). A better customized implementation would be by extending the Window class and customizing it using the the designer and code to get any functionality.

Window window = new Window
            {
                Title = "My User Control Dialog",
                Content = new OpenDialog(),
                SizeToContent = SizeToContent.WidthAndHeight,
                ResizeMode = ResizeMode.NoResize
            };
            window.ShowDialog();

Has worked like a magic for me. Can it be made as a modal dialog?

---

Ans : ShowDialog it self make it as Modal Dialog.. ...

As far as I know you can't do that. If you want to show it in a dialog, that's perfectly fine, just create a new Window that only contains your UserControl, and call ShowDialog() after you create an instance of that Window.

EDIT: The UserControl class doesn't contain a method ShowDialog, so what you're trying to do is in fact not possible.

This, however, is:

private void Button_Click(object sender, RoutedEventArgs e){
    new ContainerWindow().ShowDialog();
}

Place it in a Window and call Window.ShowDialog. (Also, add references to: PresentationCore, WindowsBase and PresentationFramework if you have not already done so.)

private void Button1_Click(object sender, EventArgs e)
{
        Window window = new Window 
        {
            Title = "My User Control Dialog",
            Content = new MyUserControl()
        };

        window.ShowDialog();
}