How do I know if a WPF window is opened

Question

In a WPF window, how do I know if it is opened?

My goal to open only 1 instance of the window at the time.

So, my pseudo code in the parent window is:

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Answer 1

Is that you search ?

if (this.m_myWindow != null)
{
    if (this.m_myWindow.IsActive) return;
}

this.m_myWindow = new MyWindow();
this.m_myWindow.Show();

If you want a singleton, you should read this : How can we create a Singleton Instance for a Window?