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Building Modern Windows Desktop Apps with WinUI 3

WinUI 3 is Microsoft's modern, native UI framework for Windows desktop development, and the recommended foundation for new desktop work. Starting with "what is WinUI 3?," this webinar walks you through the anatomy of a real project. You'll see how the CommunityToolkit.Mvvm source generators make MVVM effectively boilerplate-free, turning a handful of attributes into fully wired properties and commands. Then, in a pair of short live demos, we'll show how design tokens and styles let you rebrand an entire application in just two edits. We'll also cover the practical realities of migrating an existing WPF app to WinUI 3 — the concepts that carry over and the gotchas that don't. You'll leave with a clear mental model and the resources to start building today.

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Page # Building Modern Windows Desktop Apps with WinUI 3 June 24 | 1 pm EDT
About ICS Page 2 We Build Embedded Systems for What’s Next Accelerating next-gen product development through expert engineering and advanced software solutions. At a Glance ● Founded: 1987 ● Headquarters: Waltham, MA (Greater Boston) ● Global Offices: California, Canada, Europe ● Team: 160+ expert engineers & innovators ● Full-stack software development for regulated & high-reliability industries Centers of Excellence ● Medtech Software ● Software Development ● AI/ML Innovation ● UX/UI Design & Human Factors ● IoT & Embedded Software ● Cybersecurity
Page 3 ● What WinUI 3 is ● What makes it different ● The developer experience ● Live demos ● Converting to WinUI 3 ● Wrap-up + Q&A Agenda
What is WinUI 3? Page 4
1 2 3 WinUI 3 is… Microsoft's modern, native UI framework for Windows desktop apps Ships as part of the Windows App SDK — decoupled from the OS The UI layer of a broader API bundle (windowing, lifecycle, notifications, resources) Page 5
Your language, your choice ● WinUI 3 sits on the WinRT projection layer — it is not C#-only ● Write your apps in: ○ C# (via .NET — the most common path) ○ C++/WinRT ○ Rust/WinRT Page 6
Why WinUI 3 Exists ● Native performance no web layer, no Chromium wrapper ● Modern Fluent design language ● Ships independently of Windows not gated by OS update cadence 7 Page 7
Page 8 Framework Status Where it fits WPF Mature, actively maintained Existing investment; not the target of new UI investment UWP Maintenance only Sandboxed Store apps; deprecated for new work WinUI 3 Active, recommended Modern Windows desktop native, unsandboxed MAUI Active Cross-platform (uses WinUI on Windows under the hood) Where WinUI 3 Fits in the Microsoft Environment
What Makes WinUI 3 Different Page 9
Fluent Design System, native: ● Light / Dark modes ● Rounded corners ● Acrylic — translucent material ● Mica — window tinted by the desktop wallpaper Your app looks first-party with zero custom theming. ● Visual Layer — the same composition engine that draws the Windows shell ● SwapChainPanel — hardware-accelerated DirectX surfaces ● World-class inking / pen input via direct interop ● MRT Core — Modern Resource Technology: lighter apps, faster startup, quicker resource lookups You own the whole window The Shell’s own graphics engine ● AppWindow APIs — sizing, positioning, snapping ● ExtendsContentIntoTitleBar — blend your own UI (search, tabs, avatar) straight into the title-bar strip Windows 11 look and feel Page 10
Demo #1: Theme Switching themes is a simple one line change.
Modern, decoupled, web-ready Page 12 ● Ships as a NuGet package (Windows App SDK) not baked into the OS ○ Unlike UWP, new controls and fixes arrive without a Windows update — you upgrade on your schedule ● WebView2 — embed Chromium web content natively, no performance penalty on the native shell ○ WinUI itself is native; web content is there when you want it
Modern Controls ● New and improved controls ● Rich Microsoft library built in ○ Pivot ○ Navigation View ○ InfoBar ○ AutoSuggestBox ○ And more ● No more bolt-ons needed Page 13
Anatomy of a Project Page 14
A freshly-created WinUI 3 project: ● App.xaml / App.xaml.cs — application entry point and resources ● MainWindow.xaml / MainWindow.xaml.cs — your first window ● Package.appxmanifest — app identity and packaging ● Assets/ — icons and images The Project Core Page 15
The XAML mental model ● XAML is object instantiation in markup — <Button Content="Save"/> ≈ new Button { Content = "Save" } ● Declarative, not imperative — the nesting tree is the layout; no new-up-and-add loop ● Markup + code = one partial class, tied together by x:Class ● InitializeComponent() loads the tree and wires up the named elements ● x:Name gives you a typed field handle to a control ● x:Bind — compile-time, type-safe bindings Page 16
Declarative UI ● The imperative way: new a control, set properties, add to parent, repeat — layout only exists after the code runs ● The declarative way: the tree's shape is the screen, in one place, visible at a glance ● Tooling can render it (Hot Reload) ● A typical app shell: header + nav bar + content Frame, declared as one tree ○ Pages swap into the Frame; the header and nav bar (declared outside it) persist untouched Page 17
App lifecycle ● App.xaml.cs constructor → OnLaunched → MainWindow activation ● Work done before InitializeComponent() matters ○ e.g. set PrimaryLanguageOverride for locale before init, so x:Uid strings resolve correctly Page 18
Demo #2: MVVM Source Generator
Demo #2: MVVM Source Generator CommunityToolkit.Mvvm's source generators eliminate all the INotifyPropertyChanged boilerplate. All of it. One attribute on a private field [ObservableProperty] and the generator produces a full public property with change notification and partial callbacks. One attribute on a method [RelayCommand] and the generator produces a typed IRelayCommand property exposed to XAML Page 20
Page 21 WinUI 3 Developer Experience
Open Source & Community Driven ● WinUI 3 is fully open source on GitHub ● Community contributions welcome ● Transparent development roadmap ● Access to source code for debugging and customization Open ecosystem Page 22
XAML Hot Reload: Iterate Faster ● Change XAML without restarting the app ● See changes instantly ● Boosts productivity significantly Real-time UI iteration Page 23
● CommunityToolkit.Mvvm source generators ● [ObservableProperty] private string _name; → full Name property + change notification ● [RelayCommand] private void Save() { ... } → SaveCommand exposed to XAML ● The magic word: partial class x:Bind vs Binding: Binding is runtime reflection that fails silently; x:Bind is compile-time and faster. MVVM the modern way Page 24
Demo #3 Step Rebrand
Demo #3: Step Rebrand ● Rebranding in WinUI 3 is a two-commit operation: first swap raw hex for a named token ({ThemeResource Brush.Brand.Primary}), then promote repeated setters into a Style. ● The genuinely WinUI-specific payoff is ResourceDictionary.ThemeDictionaries: declare Light and Dark variants once, and the runtime switches every {ThemeResource} lookup automatically with zero C# code. Page 26
● Tokens + implicit styles are the XAML platform model shared by WPF, UWP, Uno, Avalonia ● WinUI 3 adds theme dictionaries (ResourceDictionary.ThemeDictionaries + ThemeResource) ○ Define your tokens once per theme light, dark, and high-contrast fall out for free ○ No extra code, no DynamicResource plumbing ● All cleanly packaged up Page 27 What WinUI adds on top
● ORM: maps .NET classes to database tables, no hand-written SQL required ● Available for any .NET language C#, F#, VB.NET (not C#-only) ● Code-First: define your model in code, EF generates the schema from it ● DbContext tracks changes, translates LINQ to SQL, manages the connection ● I.e. DbSet<Product> = the Products table ● NuGet: Microsoft.EntityFrameworkCore.Sqlite + Microsoft.EntityFrameworkCore.Tools Page 28 What is Entity Framework?
● Embedded: Runs in-process, no server to install or configure ● Single file: The entire database is one .db file ● MSIX-friendly: Store in ApplicationData.Current.LocalFolder, survives package updates ● Official Microsoft package not a third-party add-on ● File doesn't need to exist MigrateAsync() creates it on first launch Page 29 Why SQLite for a Desktop App?
● Schema lives in your repo and versions with your C# classes ● A few key commands: ○ dotnet ef migrations add <Name>: Generates a migration class with Up() and Down() ○ dotnet ef database update: Applies pending migrations, creates the DB if it doesn't exist ○ Call context.Database.MigrateAsync() at app startup to auto-apply on launch ○ EnsureCreated() skips migrations: Fine for demos, not for production Page 30 Migrations: Schema as Code
Demo #4 EF Core + SQLite End to End
1. Define the model and DbContext: one class, one context 2. Dotnet ef migrations add InitialCreate 3. Dotnet ef database update 4. Add a column → second migration → existing data survives Page 32 Demo #4: EF Core + SQLite End to End
Converting to WinUI 3 Page 33
Page 34 WPF concept WinUI 3 equivalent Binding (runtime) x:Bind (compile-time) DataTrigger / Trigger VisualStateManager + behaviors Dispatcher DispatcherQueue DataGrid (in-box) CommunityToolkit.WinUI.UI.Controls. DataGrid (NuGet) ClickOnce MSIX or unpackaged loose-file deployment app.config appsettings.json + Microsoft.Extensions.Configuration INotifyPropertyChanged boilerplate CommunityToolkit.Mvvm source generators App.OnStartup App.OnLaunched + window activation How do I convert to WinUI 3?
Wrap Up Page 35
● Native performance ● Modern Fluent design language ● Ships independently of Windows ● Modern WINUI 3 applications with community toolkit offer a simple framework for creating and editing 36 Key Takeaways Page 36