We create Class Library in .Net to reuse our code or to make our code reusable with the same type of application only, but that might not work for some conditions. Here we assume, we have created the class library for WPF or any other kind of application. And if we want to access the same type of class library for Windows 8 or Windows phone application, then in this scenario, we can't refer this as a class library.
We want the same application for all the platforms to make our life easy. We want the same application used on multiple platforms. Microsoft technology is growing day by day, and it covers every device. All types of applications we can build and validate within one framework on all types of platform Windows, Web, Mobile, or Tab.
PCL solves this problem. .Net 4.5 introduced the Portable Class Library (PCL) for developing the business logic in one location, and we can use this library end to end in all types of applications or all platforms (Windows, web, or Mobile) on .Net Framework.
The figure shows the flow of the Portable Class Library (PCL). All these applications run on the .Net Framework. All these applications have different environments and platforms, but they all can easily use the Portable Class Library. In other words, we can say that we only need to prepare the UI and do the DataBinding of our application for all the windows, web and mobile, because the same business logic can then use the entire platform.
Shared Project
A shared project is a project that contains standard code and linked to each specific platform library or App. It is compiled as a part of the platform-specific code. To develop a nice solution that is based on a shared project, there is a need to architect it to have the core features in the shared project. Here possibly, we may use partial classes, abstract classes, and interfaces to manage the objects which are specific for each platform in the platform-specific project. These kinds of projects are good when we are in a prototype phase because it is fast to implement the shareable project for the common code. We can use all the advantages of the platform-specific Framework.
