So far, from the previous recipe, we have created a blank solution and a class library that uses the full .NET Framework. In this recipe, let's create a classic Windows Forms application that uses the class library created in the previous recipe. We are going to build a Windows form that takes a name using a text box and a button, and that triggers the public method we have created in the class library. 

For this recipe, you will require the solution and the class you built in the previous recipe. Open Visual Studio 2017 and prepare for the project. Click Build | Build Solution, or press Ctrl + Shift + B, and the solution should build successfully. Everything's ready for testing our class library. 

1. Open Visual Studio 2017.
2. Now open the solution from the previous recipe. Click File | Open | Project/Solution, or press Ctrl + Shift + O, and select the Chapter1.Library solution. 
3. Now click on the Chapter1.Library solution label. Click File | Add | New Project....
4. In the Add New Project template dialog box, expand the Visual C# node in the left-hand pane. 
5. Select Windows Classic Desktop and select Windows Forms App (.NET Framework) in the right template pane:

6. Now, in the Name: textbox, type a name for the new project. Let's type Chapter1.Library.HelloWindowsForms and leave the Location: textbox as it is and the defaults as well. Click OK to create the new project.

7. The new project will be added to the Solution Explorer and it should look like this: 

8. Now let's do some cleaning of the names. Change Form1.cs to MainForm.cs. Remember, giving a meaningful name to your files is very important and a very good practice. 
9. Select the Form in the MainForm [Design] tab and go to the Properties window (or press F4). Now change the Text property to Hello World. 

10. Let's add some UI components to the form. Go to the tool box window (or press Ctrl + Alt + X ) and drag and drop a Label, a TextBox, and a Button to the form. Arrange them as per the following screenshot: 

11. Let's change some properties of the components we just dropped on the form. Go to the Properties window and change the defaults to the following:

After the changes, the Windows form designer should look like this: 

12. Let's add our library to the Windows Forms project. To do this, expand References under the Chaper1.Library.HelloWindowsForms project. Right-click on the References label and select Add Reference....
13. Under the Reference Manager dialog box, click on the Projects label in the left-hand pane. In the middle pane, check the Chapter1.Library.HelloLib project: 

14. Click OK.
15. Now double-click on the Say Hello button to open the code window. 
16. In the code window, scroll to the top and type the following code, at the end of  the very last line of using directive:

      using Chapter1.Library.HelloLib;

17. Now scroll down to the HelloButton_Click method. In between the curly brackets, type the following code: 

      var helloMessage = new HelloWorld();
      var yourName = NameTextBox.Text;
      MessageBox.Show(helloMessage.SayHello(yourName));

18. Time to test our classic Windows application with the class library created in the previous recipe. Hit F5 to debug the code. Now you should see the Windows form created. 

19. Type your name in the text box and hit the Say Hello button. A message box will appear with a message from the class library: 

20. Congratulations!!! You have just used a class library from a classic Windows application. 

If you have a closer look at the recipe we just completed, we have used a solution created from a previous recipe. In a real-world application, this is a day-to-day process. From steps 1 to 7, we opened an existing solution that contained the class library from the previous recipe and added a Classic Windows Forms application to the solution. 

In steps 8 to 11, we prepared the Windows Form projects. Proper naming of the components and files is good practice. Even though this is a small application, proper naming is a good discipline. Steps 12 to 14 are the most important steps in this recipe. In these steps, we have added our class library to the Windows project as a reference. Now you can access all the public methods given by the class library from your Windows application. 

In steps 15 to 17, we have added code to the button click event of HelloButton. Double-clicking on a component will get you to the C# code of the Windows form. Visual Studio will generate the code for you. In this case, it's the button click event. The default event of a component will vary depending on the component you have selected. In step 17, we created a variable to hold the instance of the HelloWorld class from the class library created. Then, we created another variable to hold the user input to the text box. The last line of code will call the HelloWorld.SayHello(string name) method with the string parameter supplied from the variable created in the previous line of code. Finally, a default message box will display the string returned from the SayHello(string name) method from the HelloWorld class. 

Step 19 will execute the default project, in this case, our Windows-based application. Sometimes, if the class library project is selected as the default project, Visual Studio will complain that you cannot execute this sort of project. So make sure you have selected the Windows project as the default startup project.