Multi Plaftorm Targeting using Portable Class Libraries - An Introduction

I have been putting off the discussion about portable class library tool for a long time now. But since Microsoft has released RC2 of the tool this month with exciting new features, it is very appealing to carry the message forward to followers of my blog.

Multi-platform targeting has been a big issue when we want to reuse our code for these platforms. It is common when we are working on a rich UI application with Silverlight and WPF interfaces. It has been so difficult to reuse our code because of incompatible class libraries. Silverlight does not support regular class libraries targeted for Windows platform and we need to create separate Silverlight Class Libraries.

Existing Workarounds for Multi-Targeting:
There are several workarounds developed to cope with this issue. One of them is project link. We create links between project to use types from the other project.

Project Linker:
This is a Visual Studio Add-on provided by Microsoft P&P. It makes life easier for linking the project items in multiple projects. If we link a project with another project, then if an item is added in the source project, the same item is added to the destination project. For a long time, developers have used this to be the only option for multi-targeting to WPF and Silverlight projects.

http://msdn.microsoft.com/en-us/library/ff648745.aspx

This can be downloaded from Visual Studio Gallery from here:

http://visualstudiogallery.msdn.microsoft.com/5e730577-d11c-4f2e-8e2b-cbb87f76c044/

Once installed, it can be used to add a project link to a destination project. Just right click a project and select Add Project Link. You can then specify the source project.

Adding Existing Item as Link: . This is the same thing as "Project Linker" does. It is just doing the same thing manually. Add an item in source project. Go to destination project, add existing item and make sure that you add it as link.

Pre-requisite:
Visual Studio 2010 sp1 or Visual Studio 2011 can be used to create portable class libraries. We do need to install Portal Library Tools. It can be downloaded from Visual Studio Gallery [http://visualstudiogallery.msdn.microsoft.com/b0e0b5e9-e138-410b-ad10-00cb3caf4981]

We can also use Extension Manager to install Portable Class Library.

Installation On Build Machines
In this time and age, you wouldn't find an organization with no Continuous Integration [CI] support. Mostly they use Jet Brain's Team City or Cruise Control .net. The pre-requisite described above are for development machines. Portable Class Library tools can be installed on build machines using /buildmachine switch. From msdn:

Run the installation program from a Command Prompt window, and include the /buildmachine switch on the command line.

Creating Portable Class Library Project
After installation of extension in Visual Studio 2010 Sp1, a project template is added for creating portable class library project. It is also available in Visual Studio 2011. We can find it in Add New Project dialog as follows:

While creating the project, an option is provided to select the required target frameworks. We can select the supported .net, silverlight and WP frameworks. It also supports the selection of XBox 360 and Metro Style App support.

These options can also be changed later on from the project's Properties page. Please notice the new Library tab available. Here we can select the target frameworks. This is equivalent to Application tab of .net framework class library where we can select the target framework.

Please not that there are other tabs too which are not available for portable class libraries.

Feature Set & Selected Frameworks:
The feature set available for portable libraries depend on the selected target frameworks. There is a universal set of feature supported by all the frameworks which are possible targets. Out of these universal features, each individual framework would support a subset.

It is very tempting to select all available frameworks for target. But doing that is limiting ourselves. As described above each framework would only support a subset of available features. Selecting multiple frameworks would make only the intersection of the features of supported frameworks. In the following example, we are selecting the .net framework and Silverlight as target frameworks. The available feature set is the overlapping area between two circles [Remember Venn diagram from your statistics courses :)]. If this is .net framework 4, then the library wouldn't have any view model support.

This could be further limiting if we select other frameworks.

Selecting all frameworks would only provide the little overlapping features supported by all frameworks.

This shouldn't be a limiting factor for your development. The library which is supposed to be shared across different platform would never have such code which have a dependency for a particular framework. The selected frameworks is basically an indication that the code is generic enough that it could be shared across these platforms.

The following subset is available for Silverlight 4, .Net for Metro style app and Windows Phone 7 platforms.

The following is the list of available libraries for the multiple targets of .net framework 4.0.3, Silverlight 4, Windows Phone 7, .Net for Metro style apps and Xbox 360.

Please not that if there is an additional framework which could also be selected without any effects to the available set for the selected frameworks than it is automatically selected.

Referencing Portable Libraries and Portable Library References:
Portable libraries cannot add references from non-portable libraries. Here ClassLibrary1 is a .net framework 4.0 class library. An attempt to add a reference to the portable class library causes the following:

Portable Library references can be added to regular libraries belonging to the supported frameworks. The same error message is displayed if an a portable library's assembly references is being added to an unsupported framework.