Finding IWin32Window in WPF

Copyright © 2011, Steven E. Houchin

I'm developing a WPF desktop application (C# and .NET 3.5) that needs to pop up a dialog window allowing the user to browse for a folder.  .NET provides a convenient (and bland) dialog that does this: System.Windows.Forms.FolderBrowserDialog. To pop up this dialog as modal from my app, I must call its ShowDialog method. Since I want it to be a child of my main window, I need to pass it the parent window, which should be straightforward given the "owner" parameter to the method in question:

DialogResult ShowDialog(System.Windows.Forms.IWin32Window owner);

The problem is, the would-be parent window of that dialog is of type System.Window, not IWin32Window, so "this.Owner" won't match the datatype of ShowDialog's "owner" parameter.  So, given that I have a WPF System.Window-derived parent class, where do I obtain an IWin32Window object?

Well, it turns out I have to write a tiny bit of code for it. Specifically, I must implement the IWin32Window interface on the parent window's class:

public partial class Main : Window,
    System.Windows.Forms.IWin32Window
{
...
   #region IWin32Window implementation
   IntPtr System.Windows.Forms.IWin32Window.Handle
   {
      get
      {
         return ((HwndSource)
             PresentationSource.FromVisual(this)).Handle;
      }
   }
   #endregion
...
}

With the IWin32Window.Handle property now implemented in the parent class, I can simply call ShowDialog(this). Note that you must also include a "using System.Windows.Interop" for this to work.