Choosing Windows Runtime Components versus Portable Code Library

Question

When sharing code between Windows Phone 8 and Windows 8, the two core options for developers are 1) Windows Runtime Components and 2) Portal Class Libraries.

Windows Runtime Components use WinRT and can be projected into all the supported languages. They require linked files in separate projects (binaries) when used on different platforms. They, however, share 90% of the available WinRT APIs.

Portable Class Libraries are a subset (sometimes a significant subset) of the BCL that has binary compatibility across platforms. They can be used on WinRT applications but also on other project types like Silverlight, Xbox, etc.

When a developer is choosing a "sharing strategy" which project type is the go-to technique to do the best job sharing code between Windows Phone 8 and Windows 8? Thanks.

Answer 1

It depends what form of sharing you need:

1) If you have a common C++ business logic layer you can use Windows Runtime (WinRT) components to expose this to both Windows Phone and Windows Store app (that's the only use-case for Windows Phone as you can't write a WP8 app using JavaScript or use .NET to author a WinRT component).

You'd have to build two separate WinRT components however, one for Phone and one for Windows Store. It should be possible to share the C++/CX code of your WinRT interop layer using preprocessor directives (#if) to mark the platform specific code.

2) You have business logic in C#/VB that only has dependencies on the .NET APIs which are available in a Portable Class Library. Then you can use Portable Class Library (PCL) to contain that logic. Basically if you can build your library into a PCL DLL then this should work. You can then reference this PCL in binary form in both Windows Phone and Windows Store app.

However as Martin has said you need to take care when using 3rd party libraries as these will also need to be built for PCL. Some 3rd party libraries are already available in PCL form (JSON.NET for example).

3) You want to share code for that has platform API dependencies (or 3rd party library dependencies) which are not supported by PCL. Then you'd need to create separate DLL libraries, one per platform. You can avoid code duplication using linked C#/VB source files and use a build flag (#if again) to allow small code changes between your target platforms.

Answer 2

If you want to share code between Windows Phone 8 and Windows 8, then you cannot use Windows Runtime Components, because there are different components used for Windows 8 and different for Windows Phone 8 and they are not interchangeable.
I would go for either Portable Class Libraries for some simple generic libraries, or for code sharing via links and #if WP8 compilation directives - this just works and is more powerful than Portable libs.
Keep also in mind that most external libraries like MVVM Light cannot be referenced in Portable Libs, so if you want to use them, you have to use the code sharing via file references.