Windows 10 and UWP application development

While taking a leap forward with the launch of Windows 10, Microsoft also blended the best of what worked in previous versions of Windows. They brought back the start menu, but its contents look an awful lot like the Windows 8 home screen experience. In addition to an alphabetized list of all installed apps, there is a resizable area for pinned app tiles. In fact, when running Windows in Tablet Mode, the start menu can transform into the Windows 8-style home screen experience for better usability on a touchscreen.

When Microsoft launched Windows 10, they also introduced UWP applications to Windows developers. While UWP apps have their roots in the XAML apps of Windows 8, there are some key differences that give developers some major advantages when building apps for the platform.

A key advantage is in the Universal aspect of these apps. Microsoft builds versions of Windows 10 to run on different device families, listed as follows:

• Desktop (PC)
• Xbox
• Mobile (Windows Phone)
• HoloLens
• IoT
• IoT Headless
• Team (Surface Hub)

UWP developers can build apps to target any of these devices. There is a single base set of Windows APIs shared across all these targets, and specialized SDKs available for the device-specific APIs of some families—for example, there is a Mixed Reality Toolkit and SDK for HoloLens development. With UWP, it is possible to create a single project to target many device families—for instance, you can create a project that creates apps for Desktop, Xbox, and Team families.

Because the UWP XAML for building the app's UI is the same, the learning curve for cross-device development is lowered and code reusability is very high. The nature of XAML provides a UI flexibility to adapt to different device sizes and aspect ratios.

Language choice with UWP development

While the underlying UWP APIs were written in C++, UWP developers can choose from a number of programming languages when building apps for Windows. UWP projects can be created with any of these popular languages:

• C#
• C++
• F#
• Visual Basic .NET (VB.NET)
• JavaScript

You may be surprised to see JavaScript on the list. During the Windows 8.x days, developers could create JavaScript apps with APIs known as WinJS apps. Today, Microsoft has created a branch of React Native for Windows developers, known as React Native for Windows. These JavaScript client apps have full access to the same Windows APIs as other UWP apps and can be packaged and deployed through the Windows Store.

Note

React Native for Windows is an open source project hosted by Microsoft on GitHub at https://github.com/Microsoft/react-native-windows.

While many of the UWP apps developed for Windows 10 by Microsoft are created with C++, most other developers choose C#. We will also use C# when building our app throughout the course of this book.

Lifting app restrictions

As discussed earlier, apps built for Windows 8 had a number of restrictions that have been either removed or relaxed with UWP.

First and foremost, today's UWP apps can run in resizable windows, just like any other Windows desktop application. The trade-off is that developers now need to test for and handle the resizing of their app to almost any size. The dynamic nature of XAML can handle much of the resizing very well, but below a certain minimum size, scroll bars will need to be employed.

For end users, one of the benefits of using UWP apps is the inherent security they provide due to the limited access of apps to the PC's filesystem. By default, each app can only access its own local storage. In 2018, the Windows developer team announced a new feature for UWP developers. By adding some app configuration declaring which additional types of access the app requires, applications can request access to additional parts of the filesystem. Among them are the following:

• User libraries, including Documents, Pictures, Music, and Videos
• Downloads
• Removable devices

  Note

  There are additional filesystem permissions that can be requested. See the Microsoft documentation for an entire list: https://docs.microsoft.com/en-us/windows/uwp/files/file-access-permissions.

Any additional permissions requested will be declared on the app's listing on the Windows Store.

Some less common scenarios are now available to UWP apps on Windows 10. Developers can add some configuration and startup code to enable multiple instances of their app to launch. While it would seem that the point of a UWP app is the XAML UI, it is now possible to create a UWP console app. The app will run at the command line and have access to Universal C runtime calls. Developers who want to get started with console apps can find project templates on Visual Studio Marketplace, at https://marketplace.visualstudio.com/items?itemName=AndrewWhitechapelMSFT.ConsoleAppUniversal.

UWP backward compatibility

No UWP app is compatible with any version of Windows before Windows 10. Beyond this, each UWP app must declare a Target Version and a Minimum Version of Windows with which it is compatible. The target version is your recommended version, which will enable all of an app's features and functionality. The minimum version is, unsurprisingly, the minimum version of Windows that users must have to be able to install an app from the Windows Store.

Visual Studio will prompt you to select these versions when creating a new UWP project. If the two are the same, it keeps things simple. You will have all of the APIs of that SDK version available to the app. If the target version is greater than the minimum version, you need to add some conditional code to light up the features of any versions greater than the minimum. The app must still be useful to users running the minimum version; otherwise, it is advisable to increase the minimum. If any of the newer APIs or controls are fundamental to the app, it is also recommended that the minimum version be increased to one where those are available.

Note

For more information on writing the conditional or version adaptive code, see the Microsoft documentation here: https://docs.microsoft.com/en-us/windows/uwp/debug-test-perf/version-adaptive-code.

If you are creating .NET libraries that will be referenced by your UWP project and you would like to share them across other platforms, perhaps by a Xamarin mobile app, a .NET Standard version should be targeted by the shared library project. The most common .NET Standard version today is .NET Standard 2.0. To reference a .NET Standard 2.0 project from a UWP project, the target version of the UWP project should be 16299 or later.

The primary benefit of WinUI over UWP is that it lessens the dependency of Windows apps on a particular version of Windows. Instead, the controls, styles, and APIs are maintained outside of the Windows SDK. As of this writing, the minimum version required for a WinUI 3.0 app is 17134 or higher, and the target version must be set to 18362 or higher. Check the latest WinUI documentation for the current minimum requirements.

The hope for WinUI is to bring a greater number of controls and features to more supported versions of Windows 10 as the project matures.