Class Libraries

Class Libraries

Besides Windows Forms Applications, the other type of Visual Studio project that we will be building in CIS 300 is a Class Library. A Class Library is not a stand-alone application, but rather a collection of code that can be used by various applications. The .NET Framework is a collection of class libraries. When we implement a data structure, we often want to place it in a class library so that it is available to a variety of applications.

While it is possible to create a solution containing a single project that is a class library, in CIS 300, we will also work with solutions containing both a Class Library project and a Windows Forms Application project that will use the class library. We therefore need to know how to create a new class library project within an existing solution.

Suppose, for example, that we have a solution containing the program from the section, “ StringBuilders” (this solution may be obtained by creating a Git repository using this URL). We wish to replace the implementation of StringBuilder from the .NET Framework with the class defined in “ Implementation of StringBuilders”. Furthermore, we wish to place this class in a new class library. To create a new Class Library project within this solution, right-click on the solution name in the Solution Explorer (i.e., on the top line), and select “Add -> New Project…”. From the resulting dialog, select “Class Library (.NET Framework)” and name it Ksu.Cis300.StringBuilderLibrary. For the location, use the folder containing the Git repository that includes the Visual Studio solution, so that this project will be included in the same Git repository.

When the project is created, a code window containing a template for a public class definition will appear. There will be no Design window, as you are not building a graphical application (although graphical controls can be built within a class library). The names of the source file and the class should now be changed to StringBuilder using the Solution Explorer in the same way as for a Windows Forms Application. Code for the StringBuilder class can now be copied either from the section, “Implementation of StringBuilders” or the Git repository created using this URL. Although we don’t need them for this example, additional class files can be added to the project by going to the Solution Explorer, right-clicking on the project name (not the solution name), and selecting “Add -> Class…”.

Just having this project in the same solution isn’t enough to allow the Ksu.Cis300.StringsAndStringBuilders project to access it. In order to enable this access, we need to go back to the Solution Explorer, right-click on the Ksu.Cis300.StringsAndStringBuilders project, and select, “Add -> Reference…”. In the resulting dialog, we open the “Project” group on the left and select “Solution” from that group, then click the box next to “Ksu.Cis300.StringBuilderLibrary” in the main panel, and click the “OK” button at the lower right. Once this is done, we can edit “UserInterface.cs” in the Ksu.Cis300.StringsAndStringBuilders project we just added, and change

using System.Text;

to

using Ksu.Cis300.StringBuilderLibrary;

Then wherever the class StringBuilder occurs in this file, the implementation in our class library will be used.