I'm writing a WPF app, and I'd like to make use of this library.
I can get an IntPtr for the window by using
new WindowInteropHelper(this).Handle but that won't cast to System.Windows.Forms.IWin32Window, which I need to show this WinForms dialog.
How do I cast IntPtr to System.Windows.Forms.IWin32Window?
OPTION 1
IWin32Window only expects a Handle property, which is not too difficult to implement since you already have the IntPtr. Create a wrapper class that implements IWin32Window:
public class WindowWrapper : System.Windows.Forms.IWin32Window { public WindowWrapper(IntPtr handle) { _hwnd = handle; } public WindowWrapper(Window window) { _hwnd = new WindowInteropHelper(window).Handle; } public IntPtr Handle { get { return _hwnd; } } private IntPtr _hwnd; } You would then get your IWin32Window like this:
IWin32Window win32Window = new WindowWrapper(new WindowInteropHelper(this).Handle); or (in response to KeithS' suggestion):
IWin32Window win32Window = new WindowWrapper(this); OPTION 2 (thx to Scott Chamberlain's comment)
Use the existing NativeWindow class, which implements IWin32Window:
NativeWindow win32Parent = new NativeWindow(); win32Parent.AssignHandle(new WindowInteropHelper(this).Handle); 
new WindowWrapper(this) and you have something to pass in as an IWin32Window.
NativeWindow class. Just call AssignHandle(IntPtr) with the handle from the function provided by the OP.
System.Windows.Forms.IWin32Window win32Window = new System.Windows.Forms.NativeWindow(); win32Window.AssignHandle(new WindowInteropHelper(this).Handle); ...results in the compile error "IWin32Window does not contain a definition for AssignHandle". I tried using the System.Windows.Interop version of IWin32Window but that doesn't have a NativeWindow() method.
AssignHandle is a method of NativeWindow and not IWin32Window. You would need to cast to NativeWindow or declare win32Window as a NativeWindow before the AssignHandle method is available . I'll update the answer