WPF, Hook Window, Popup

Question

In App.xaml.cs or in another starting class instance you need add:

var field = typeof(PresentationSource).GetField("RootSourceProperty", BindingFlags.NonPublic | BindingFlags.Static);
        var property = (DependencyProperty)field.GetValue(null);
        property.OverrideMetadata(typeof(DependencyObject), new FrameworkPropertyMetadata(property.DefaultMetadata.DefaultValue, OnHwndSourceChanged));

Where, RootSourceProperty is private field DependecyProperty of PresentationSource. Its property use when HwndSource is created and set RootVisual. So you need just use property changed call back of RootSourceProperty:

private static void OnHwndSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {

    }

This is nice because, you can use it in your all Application and for all HwndSource (Popup, Window or Custom controls, where you are using HwndSource)