Occurs when the IsOpen property changes to true.
public event EventHandler Opened
<object Opened="EventHandler" .../>
A Popup is opened and closed by toggling the IsOpen property.
The following example shows how to define an event handler for the Opened event.
private void PopupOpening(object sender, EventArgs e)
//Code to execute when Popup opens
<TextBlock Background="Yellow">Popup Text</TextBlock>