Custom attribute classes in C Sharp (C#) - Mini Project: Build & Apply

Custom Attribute Classes in C#

📖 Scenario: Imagine you are building a simple library system. You want to mark some classes with special notes using custom tags called attributes. These tags will help you add extra information to your classes, like marking a class as "Important" or "Deprecated".

🎯 Goal: You will create a custom attribute class, apply it to a book class, and then read the attribute information using code.

📋 What You'll Learn

Create a custom attribute class called InfoAttribute with a string property Note.

Create a class called Book and apply the InfoAttribute with a note.

Write code to read and print the Note from the InfoAttribute applied to the Book class.

💡 Why This Matters

🌍 Real World

Custom attributes are used to add extra information to code elements, which can be read at runtime to change behavior or provide metadata.

💼 Career

Understanding custom attributes is useful for working with frameworks, libraries, and tools that use metadata, such as serialization, validation, or documentation generation.

1

Create the custom attribute class

Create a public class called InfoAttribute that inherits from System.Attribute. Add a public string property called Note with a getter and setter.

C Sharp (C#)

// Your code here

Need a hint?

Remember, custom attributes must inherit from System.Attribute. Use public string Note { get; set; } to create the property.

2

Create the Book class and apply the attribute

Create a public class called Book. Apply the InfoAttribute to the Book class with the note set to "This is an important class".

C Sharp (C#)

using System;

public class InfoAttribute : Attribute
{
    public string Note { get; set; }
}

// Create the Book class below and apply InfoAttribute
// Your code here

Need a hint?

Use square brackets [] to apply the attribute above the class. Set the Note property inside the parentheses.

3

Write code to read the attribute

Write code to get the InfoAttribute applied to the Book class using typeof(Book).GetCustomAttributes(typeof(InfoAttribute), false). Store the first attribute in a variable called infoAttr of type InfoAttribute.

C Sharp (C#)

using System;

public class InfoAttribute : Attribute
{
    public string Note { get; set; }
}

[InfoAttribute(Note = "This is an important class")]
public class Book
{
}

// Get the InfoAttribute from Book class
// Your code here

Need a hint?

Use GetCustomAttributes on the Book type to get the attributes. Cast the first attribute to InfoAttribute.

4

Print the note from the attribute

Add a Console.WriteLine statement to print the Note property of infoAttr inside the Main method.

C Sharp (C#)

using System;

public class InfoAttribute : Attribute
{
    public string Note { get; set; }
}

[InfoAttribute(Note = "This is an important class")]
public class Book
{
}

class Program
{
    static void Main()
    {
        object[] attrs = typeof(Book).GetCustomAttributes(typeof(InfoAttribute), false);
        InfoAttribute infoAttr = (InfoAttribute)attrs[0];
        // Print the Note property below
        // Your code here
    }
}

Need a hint?

Use Console.WriteLine(infoAttr.Note); to show the note on the screen.