How To Create Class Library In Visual Studio 2019

Tutorial - Class Library .DLL for C#

Published Jan 02, 2020 Last updated Jan 03, 2020

Tutorial - Class Library .DLL for C#

This tutorial shows, how to build a simple Class Library .DLL in the C# Programming Language. The Class Library .DLL contains program code, data, and resources that can be can used by other programs and are easily implemented into other Visual Studio projects.

Install Visual Studio IDE

Step 1 : Download Visual Studio Installer

Visit visualstudio.microsoft.com and navigate to the Windows Download Page
Select either the Proffessional, Community or Enterprise Edition and press the download button.
If you're an individual programmer or a small team, then i would recommend, downloading the free community edition

Step 2 : Run The Visual Studio Installer

When you have downloaded an installer of your choice, run it by double clicking the downloaded file. An installer dialog will appear on your screen.
In the Workloads Tab view, Select .NET Desktop Development if you want to develop for the Windows Desktop

Create New Class Library Project With Visual Studio

Step 1 : Create New Project

Select C# in the language tab
And then select Class Library (.NET Framework) and press the NEXT button
You can then proceed to give your project a Project Name
Call the project MathLibrary (in order to copy/paste example code)
Press the CREATE button, After you have given a name to your project

Building the Class Library .DLL for C#

The following code example is a C# version of the Class Library. The Class Library .DLL contains program code, data, and resources. The Class Library in this example will feature a custom Math API that has a set of functions to Substract, Devide and Multiply numbers

Project File Structure

Our Class Library project contains only of 1 file. The Class1.cs file which is our API containing the methods to calculate simple mathematical operations.

Class1.cs (Example Code)

The Class1.cs file is a C# class from our MathLibrary.dll that contains our methods to Substract, Multiply, Devide numbers.

Substract() Method for subtracting 2 numbers.
Multiply() Method for multiplying 2 numbers.
Devide() Method for deviding 2 numbers.
Power() Method for calculating the power a number

                              using                System;                using                System.Collections.Generic;                using                System.Linq;                using                System.Text;                namespace                MathLibrary                {                public                class                Class1                {                                  public                  float                  Substract(                    float                    a,                    float                    b)                {                return                a - b;         }                                  public                  float                  Multiply(                    float                    a,                    float                    b)                {                return                a * b;         }                                  public                  float                  Devide(                    float                    a,                    float                    b)                {                return                a / b;         }                                  public                  floa                  Power(                    float                    a)                {                return                a * a;         }     } }

Compiling Project with Visual Studio 2019

Step 1: build your project, converting the source code into an (.dll file)

To build your project, choose Build Solution from the Build menu.
The MathLibrary.dll is now created in the \bin\Debug folder of your Project

PART 2 : Using the Class Library in other Visual Studio Projects

Step 1 : Create New Console Application Project With Visual Studio

Select C# in the language tab
And then select Console App (.NET Framework) and press the NEXT button
You can then proceed to give your project a Project Name
Call the project MathApplication (in order to copy/paste example code)
Press the CREATE button, After you have given a name to your project

Console App Project File Structure

Our Console App project is relatively small and will consist of 2 files. The Program.cs which is the entry point of our application, and the MathLibrary.dll file which contains our API containing the methods to devide, multiply, substract numbers.

Adding MathLibrary.dll as a Reference

Step 1: Add the following References to your Project Solution

Add MathLibrary.dll to Project References

NOTE: to Add Custom References, click the References tab. Click the Add References button to open the Add Reference dialog box. In the Add Reference dialog box, select the Browse tab indicating the type of component you want to reference. Select the components you want to reference, and then click OK.

Program.cs (Example Code)

The Program.cs file is a C# class that contains the Main method, which serves as the entry point of our Console Application. Usually In computer programming, an entry point is where the first instructions of a program are executed. Here we will manage the Console UI, use functions from the MathLibrary.dll and display it's results on screen.

                              using                System;                using                MathLibrary;                // Importing Math Library                namespace                MathApplication                {                class                Program                {                                  static                  void                  Main(                    string[] args)                {                // Declare class from MathLibrary.dll                Class1 math =                new                Class1();                // Declare variables and use methods from MathLibrary                float                substract = math.Substract(5,                2);                float                multiply = math.Multiply(5,                2);                float                devide = math.Devide(5,                2);                float                power = math.Power(5);              Console.WriteLine("This Application uses functions from MathLibrary.dll todo simple calculations");                // Print results on screen                Console.WriteLine(substract);             Console.WriteLine(multiply);             Console.WriteLine(devide);             Console.WriteLine(power);              Console.ReadLine();         }     } }

Run Project with Visual Studio 2019

Visual Studio builds your project, converting the source code into an executable (.exe file)

To build your project, choose Build Solution from the Build menu.
To run the code, on the menu bar, choose Debug > Start Debugging. A console window opens and then runs your app.
To run the code with hotkeys, Press Ctrl + F5 to run your project

Result MathLibrary.dll & Console App Project

If everything went right the application should display the numbers calculated by the MathLibrary.dll
You can download the C# Source Code for the MathLibrary.dll & Console App Project for testing and editing Download Source Code

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