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Frequently Asked Questions
We will update this page periodically.
Note - Sometimes where this FAQ says "we will" and "can" and "is", we're stating what we want to have happen. As we build out the Windows App SDK we might change course based on feedback from you.
How do I start using the Windows App SDK in my app?
If you have a Desktop Win32 or UWP app there are multiple components available now.
These components are available for you to use now and adhere to the 'Windows App SDK Family Promise' that they have a single API for use in all kinds of applications.
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WinUI 3 for XAML in your Win32 app helps you build fluent UX with the ease of XAML. This component is part of the Windows App SDK Family of functionality, building on the identity + packaging + deployment transparent ideas that Windows App SDK supports for your app as well.
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C++/WinRT, RUST/WinRT, and C#/WinRT provide language-native projections of Windows, Windows App SDK, and your own custom types defined in metadata. Consume APIs from the Windows Kit, produce them for use by other supported projections, create your own new language projections.
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MSIX and MSIX-Core let you package your application for distribution to Windows Desktop machines via the store or your own delivery pipeline. MSIX-Core lets you use the reuse parts of the MSIX packaging story on older versions of Windows.
Coming soon
Tell us what other components you'd like to see as part of the Windows App SDK Family
Do I need to be packaged to use the Windows App SDK?
Your app does not need to be packaged to use Windows App SDK functionality.
If you are packaged using either a Universal Windows Application package or a Desktop Bridge package, referencing the NuGet package is enough to start using the Windows App SDK right away.
If you have your own installer, we'll have instructions to carry the Windows App SDK components with your app and how to install them using some common installers.
How do I contribute?
Use this repo's GitHub Issues to ask questions, start a discussion or make a feature proposal.
Is the Windows App SDK a new App Model?
No.
Windows App SDK is a set of libraries and content you add to your existing app within its app model and start coding. Some parts of the Windows App SDK work better if your app is a UWP app, or Desktop Bridge, or has identity.
Your existing app model's activation, deployment, lifecycle, and presentation will continue to work as you bring in more Windows App SDK functionality. The more functionality you use from the Windows App SDK the easier it'll be if you want to change your app model, since the same code will just keep working!
What Languages and Runtimes are Supported?
Windows App SDK's API surface will be defined in metadata similar to WinRT APIs already part of Windows. We'll support projections of that metadata through projects like C++/WinRT, C#/WinRT, and Rust/WinRT so access to Windows App SDK APIs is familiar to you.
Windows App SDK aims to directly target the Windows public API surface and does not rely on any other frameworks or runtimes, so you can use it with any runtime for which there's a projection. This means you'll be able to use the Windows App SDK without retargeting, other than a reference to the metadata + projection that's right for you.
Practically speaking, any language & runtime that can handle COM objects can support Windows App SDK. Please file an issue with a specific language or runtime in mind.
Can my App Mix Win32 and Windows App SDK?
Yes.
Windows App SDK is additive to your existing application code. If your app relies
on Win32 API constructs you can keep doing so while starting to use more
Windows App SDK functionality. Anywhere Windows App SDK wraps a lower-level
currency (like, a file HANDLE or an HWND or an HKEY) there'll be a way for
your app to grab it and "call through" Windows App SDK to the underlying Windows API
surface.
Does Windows App SDK Replace or Deprecate Win32 APIs?
The Windows Kit will continue to exist for your apps to use. Windows App SDK does not attempt to replicate or replace the breadth of the Windows Public API surface.
Windows App SDK will bring new ways to use the existing public API surface, guiding your app towards modernized constructs and code that can use new technologies on later OS versions while still working when running on older editions.
What Kinds of APIs are out of scope?
Windows App SDK can't change fundamental Windows behaviors like processes, threads, memory management, handles, tokens, security boundaries, networking, sockets, shell windowing behaviors, user identity, etc. What we can change are behaviors that are specific to your apps.
We're looking to support:
- Better app lifecycle notifications
- Bridging gaps between packaged & unpackaged, identity and non-identity apps
- Helpers that simplify transition to/from Windowing models
- Resource management for all kinds of apps (think MRT and MUI support)
- Improved access to user data from AppContainer apps
What's a UWP?
Referenced throughout this repo, the term "UWP" references a Universal Windows Platform App - an app running inside an app container, at a lower privilege level, with package identity, delivered via an MSIX. This app's lifecycle from activation through termination is controlled by the platform for best power and resource usage. Its access to the user's resources are gated by a Request model so the user is in control. Windows and views created by the app are positioned by the OS shell. Its UX is either drawn using XAML or Composition objects or a framework that produces XAML or Composition objects.
How will I consume Windows App SDK components? How will they be packaged?
Windows App SDK components will be available as NuGet packages and Framework packages. Developers can add Nuget packages to their build environments and or reference shared code that will be available as framework packages.
At developer consumption time it's a Nuget package with metadata and the things your languages need to build against it. At runtime, it's a set of DLLs distributed using a framework package. Your app doesn't need to redistribute the DLLs directly - your app would either depend on the framework package specifically (in the case of a packaged app) or would deploy our upcoming WindowsAppSDK.MSIX that contains the framework package as part of your app's unpackaged installer (similar to how an app carried the VC Runtimes or the DirectX, etc.)
What is a Framework Package?
Framework packages are ways for apps to share code from a common source, rather than carrying it with themselves. Apps just need to reference the framework package in their manifest. A user's device needs only to carry one Windows App SDK Framework package and many apps can reference it. Framework packages are updated faster than apps are e.g. When WinUI ships a new version of their framework package all three apps magically get the new version without themselves having to update (or know how to update some shared copy.) This is much better for security & reliability fixes as well.
How will consuming Windows App SDK components impact my app size?
If you are a packaged app? No. If unpackaged, it probably will.
Nuget packages are build-time artifacts. Referencing more NuGets may mean additional work at build time (like generating projections) but that’s all. At runtime, apps don’t carry the Framework Package content in their own directory. They share common binaries managed by the system. To help alleviate any DLL hell concerns, Framework Packages will not do breaking changes like the old “DLL hell” problem – we’ll be using versioning mechanisms to prevent that.
How will the Windows App SDK impact an application's performance given that the pieces are further and further away from the OS?
There's likely going to be a performance impact but it depends on the component. In some situations, like with MRT Core, there will be improved performance because we will prune some expensive but rarely used functionality. Runtime performance will be probably slightly better as the API interface flattening makes calling complex classes cheaper (fewer interface queries.). Memory usage will be slightly better overall as your apps will load code that can be improved and reduced in size over time. For performance at app launch, there'll probably be a net neutral effect.
Will the Windows App SDK help with app-compat testing of new Windows versions??
Yes. Windows App SDK components will work downlevel to at least Windows 10 version 1809 and in future versions of Windows 10. We will evaluate moving the min version over time based on the needs of developers - thinking of it as roughly aligned with Windows enterprise support is likely a good starting point
What is the deprecation strategy for in-system components?
In-box components will be supported forever in the usual way. We have no plans to deprecate them (remove their usability) at this time. We will likely slow down or pause investment in the in-box components while we focus on making the Windows App SDK surface complete.