The WinRT platform provides developers with a new way to build reusable software components. WinRT types packaged in a WinRT component, also called a WinMD component (WinRT components == WinMD components). In traditional .NET application development, you could create a dynamic-link library (DLL) as a managed class library and use it in one or more applications.

This option is still available in Visual Studio. However, you can change the output type of a library project from class library to WinRT component, and the output of such a project is a WinMD (Windows Meta Data) file.

Benefits of creating a WinMD / WinRT component.

Contrasting to the DLL files WinRT / WinMD components can be accessed by unmanaged languages like C++ and Javascript. This allows us to create a WinRT / WinMD component in a managed language (C# or Visual Basic) and use it across different Windows Store Apps (WSA) projects implemented in unmanaged languages.

But this flexibility comes with some restrictions.

• All public classes in WinRT / WinMD component should be marked sealed.
• public fields aren’t allowed.
• public data members must be declared as properties
• Data types should be WinRT / WinMD compatible
• Creating a WinRT / WinMD component in C++ has some additional property attribute settings (activatable class and ect…)

Creating a WinRT / WinMD component in C#

This is a very simple example and straight forward create Windows Store Apps (WSA) class library. Mark the class public and sealed. Create a method to return a string value.

Go to Project Properties and change the output type from Class Library to Windows Runtime Component. 

Component Code

Do the build.

Accessing the C# WinRT in Javascript

Create a WSA project in Javascript. Add the WinRT project reference to the Javascript project.

Create a Javascript method to call the WinRT method. VS intellisense would guide you.

Javascript Code.

Here you can notice that the GetDate() C# method is formatted to getDate() with Javascript naming convention.

HTML Code

Run the code. 🙂

Things to consider

When you create a WinRT / WinMD component it is specifically designed for the Windows Runtime. Windows Runtime supports different language executions. In the above Javascript project we have a WinRT component developed in C# executed in the Javascript app. This is very useful when you want to extend your existing LOBs. You can use your existing managed code with little modifications, this cuts down development cost.

And also some complex data processing codes are hard to be written in pure Javascript. You can implement those in C++ and use the component in your front facing Javascript WSA.