The compiler tells you that you are currently calling ShowDialog on a WPF window and that there's no implicit cast between bool? and System.Windows.Forms.DialogResult Fix: Call ShowDialog on a ...

Windows Forms and WinUI are available now, while WPF is only partly available, starting with System.Xaml. More components will be open-sourced over the next few months.

Microsoft open-sourced Windows Presentation Foundation (WPF), Windows Forms, and Windows UI XAML Library (WinUI). Plus, the .NET Foundation is opening up.

Microsoft open sources WPF, Windows Forms and Windows UI XAML Library, and also unveils .NET Core 3 Preview 1.

While Windows Forms and WinUI go open source today, WPF is starting with some smaller components -- System.Xaml -- with more expected in the following months.

For Blazor Hybrid, there is a control called BlazorWebView in Windows Forms as well as WPF and MAUI, which includes the Blazor application in a frame technology window.