Xamarin.Forms Walkthrough 2: The Curious Case of Code Sharing

Shared Projects

The Shared Project template was introduced with the release of Visual Studio 2013 Update 2, and Xamarin added support for these specialized projects in its release of Xamarin Studio 5.



Let's start by creating a new project in Visual Studio or Xamarin Studio and select Shared Project (Empty) template under Visual C# family. Give your new project a name, e.g. SharedProject1 and click OK.

If you didn't see a shared project template in your Visual Studio, just download and install Shared Project Reference Manager from Visual Studio Gallery.



By default, a Shared Project doesn't really contain access to any functionality at all. There is a strange thing going on here, just try to build, run or debug. It's crazy, right.? A Shared Project doesn’t actually build on its own. It's because, we build a project to transform our codes to an executable file which the system can use. Shared Project is merely a shell that contains code that will be included in other projects that reference it. There are no platforms to target or no rules to follow, this makes shared project entirely different from PCLs.

Now right click on the solution and add an Android Project to the solution. Secondly, right click on the Reference folder and select Add Shared Project Reference.



Now you can see the shared project SharedProject1, select it and click OK.



Now we can see that our shared project is added in our android project.



Now the code contained in shared project can be compiled into the referenced project. They need some other project to reference them for build and compile.

Shared project also supports some specific Compiler Directives. We can place special directives in our shared project so that specific platform can handle it differently. Some of the directives are listed here:

• __MOBILE__ : Defined in both Xamarin.iOS and Xamarin.Android projects.
• __IOS__ : Defined in Xamarin.iOS projects.
• __ANDROID__ : Defined in Xamarin.Android projects.
• WINDOWS_PHONE : Defined in Windows Phone 7 and 8 projects.
• SILVERLIGHT : Defined in Windows Phone Silverlight projects.
• __ANDROID_xx__ : Defined for specific API versions in android ( xx : replaced by targeted API version )

We can use context switchers such as #if, #else, and #endif directives which will help us point to the specific platforms in shared code.

Advantages

• Shared project can have platform specific codes.
• Support conditional compilation to allow multiple platform-specific code in a single file.
• It will allow access to libraries and all features of the parent project.
• Shared codes can be branched using context switchers based on compiler directives.

Disadvantages

• It will not support to create views using XAML.
• Unit testing became complicated since shared project contains many platform specific codes.
• Dll's are not created so codes can't be shared across other solutions.