MVVM, dependency injection and tests – learn WinUI 3 (W5, lesson 3)

What you learn in this lesson

write bindings with {x:Bind}, know that the default mode is OneTime, and always set the mode explicitly

bind a view model built with CommunityToolkit.Mvvm to {x:Bind} as a property of the page

put view models into a class library without XAML types and test them with xUnit without a window

bring changes from another thread onto the UI thread through the DispatcherQueue without the view model knowing a window

The Kladde is a Windows program with a NavigationView and pages for contacts and appointments, and the data is hard-coded. As soon as the data comes from a web API, a form has rules, and someone should review a change, the code behind the pages becomes a problem, because you can only try it out with a running window. This lesson separates the logic from the user interface until you can test it with dotnet test, and shows what WinUI 3 does differently along the way.

Where the Kladde stands

The lesson assumes W5.1.1 and W5.1.2: the packaged WinUI 3 project src/Kladde.Desktop with a NavigationView whose Frame shows the pages ContactsPage, ContactDetailPage and AppointmentsPage, with sample data in the code-behind. The web API's response types from K2 are ContactResponse (Id, Name, Email, Company, Tags) and AppointmentResponse (Title, Start, End, ContactIds). Keep your own names and carry the steps over. NewAppointmentPage is new. W2.2.1 builds the same view models for MAUI; this lesson covers what WinUI 3 does differently.

This lesson belongs to course W5

You will see the rest of this lesson and its video once you have bought the course. The goals above show what you learn here.

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