As we saw in a previous lesson, the .NET Framework Class Library is split up across several different Assemblies, each within its own .dll file in the Framework library folder:


Assemblies are split into separate files to reduce load on resources, maximize efficiency so that we load up only what is needed to complete the task at hand, and to make code portable. This lesson will demonstrate how to create Class Libraries off of your own custom project code, and how to add references to resulting .dll Assemblies.

Step 1: Create a New Project

To begin this lesson, create an ASP.NET project called “CS-ASP_041” and in the Default.aspx add a single resultLabel:


Step 2: Add another Project to the Solution as a Class Library

For this particular Solution, we will want to add another project to it. To do this right-click on the Solution and from the menu choose:

Add > New Project…


From the list of templates select “Windows” and “Class Library,” and name the project “HeroMonster”:


And now you can access both projects within the Solution Explorer. If you want, you can even build the projects separately by right-clicking on one and choosing from the menu “Build”:


Step 3: Create Custom Classes in Class1.cs

The “HeroMonster” project will come with a default class file called “Class1.cs” and in this file we will create two separate classes called Character and Dice:


Write the following code for each class:



Step 4: Add an Outside Assembly to a Project via ‘References’

You can now add the “HeroMonster” project to the CS-ASP_041 project by right-clicking it’s “References” within the Solution Explorer:


And then selecting it under the “Projects” tab:


Step 5: Incorporating the Assembly in Code via Using Directives

Now that we have a reference to this assembly in the CS-ASP_041 project, we can add it to our class files via a using directive. Note that this directive actually loads the code library from HeroMonster, whereas the assembly reference simply allows it to be available to our project. With the directive added, you can then reference a public class, such as Character, from that library:


Step 6: Porting Over the Battle Game Code

You can now fill out Page_Load() with the code we used in the previous battle simulation game project:


We will also need to port over, into this Default class, the following helper methods:


This is an identical application to what we built before, with the difference being that we partitioned out some “Domain-specific” code – the Character and the Dice classes – factoring them out into their own Class Libraries. This is noteworthy as it allows the classes to be reused in another project, which we can also accomplish by loading the .dll created in the project’s bin folder when we ran the application.

Step 7: Adding HeroMonster.dll Assembly to a New Project

Open up a new instance of Visual Studio and create a new Project based off of a Windows Forms Application template. Even though we’re not going to deal with Windows Forms in-depth, this will demonstrate how easy it is to port over our custom Class Libraries into a different project environment, requiring very little changes:


Once the Windows Form project is open, turn to the Properties Window (F4) and simply rename the project’s Design Name to “resultLabel”:


Next, right-click on “References” underneath the main project within the Solution Explorer, and select “Add Reference”:


On the next screen you will want to click “Browse” and navigate to the folder for the project we worked on at the start of this lesson. Within that folder will be a bin folder that holds the HeroMonster.dll that was automatically built when we ran the application:


Add that .dll Assembly to the project and you will see it under “References” in the Solution Explorer:


Double-click on “Form1” in the Solution Explorer to open up the code for the Form Application:


Add the HeroMonster library as a using declaritive at the top of the script:


You can then copy all of the Page_Load(), displayResult() and printStats() code from the Default.aspx.cs in the original project – that depends on the HeroMonster class library code – and paste it into the Form1 class in the current Forms project (partially represented below, substituting Page_Load() with Form1_load() ):


If you build the project and everything is set up correctly, you should notice that there are no errors. Of course, some things will have to be changed considering that the HeroMonster code was for a Web Application and contains HTML. However, the main point here is to see how you can partition your code into individual projects, Class Libraries and .dll Assemblies in order to gain portability with the code you write.

Note that you can add references to existing Framework Assemblies using the same process. This is useful whenever you have particular functionality you want to use in your project and is already available in the Framework. To add an existing Framework Assembly, once again go to:

Solution Explorer > References > Add Reference > Assemblies > Framework

And select the Assembly relevant to your project in the right-hand pane:


Lessons in this Course