How to Create Delegate in C#: Syntax and Example

In C#, create a delegate by declaring it with the delegate keyword followed by a method signature. Then, instantiate it by assigning a method matching that signature. Delegates allow you to pass methods as parameters or store them as variables.

Syntax

A delegate declaration starts with the delegate keyword, followed by the return type and the parameter list matching the methods it can point to. For example, delegate void MyDelegate(string message); declares a delegate that points to methods returning void and taking a string parameter.

To use it, create an instance by assigning a method with the same signature, then invoke it like a method.

csharp

delegate void MyDelegate(string message);

Example

This example shows how to declare a delegate, assign a method to it, and invoke the delegate to print a message.

csharp

using System;

class Program
{
    // Declare a delegate type
    delegate void MyDelegate(string message);

    // Method matching the delegate signature
    static void ShowMessage(string msg)
    {
        Console.WriteLine(msg);
    }

    static void Main()
    {
        // Create delegate instance pointing to ShowMessage
        MyDelegate del = ShowMessage;

        // Invoke the delegate
        del("Hello from delegate!");
    }
}

Output

Hello from delegate!

Common Pitfalls

• Signature mismatch: The method assigned to a delegate must exactly match the delegate's return type and parameters.
• Null delegate invocation: Invoking a delegate that is null causes a runtime error; always check or use the null-conditional operator.
• Using delegate instead of event: For event handling, use event keyword with delegates to restrict direct invocation.

csharp

using System;

class Program
{
    delegate void MyDelegate(string message);

    static void ShowMessage(int number) // Wrong signature
    {
        Console.WriteLine(number);
    }

    static void Main()
    {
        // Compilation error: signature mismatch
        // MyDelegate del = ShowMessage;

        // Correct usage:
        MyDelegate del = msg => Console.WriteLine(msg);

        // Null check before invoking
        del?.Invoke("Safe call");
    }
}

Output

Safe call

Quick Reference

Remember these key points when working with delegates:

• Declare with delegate keyword and method signature.
• Assign methods with matching signature.
• Invoke delegates like methods.
• Check for null before invoking.
• Use event keyword for event patterns.

Key Takeaways

Declare delegates using the delegate keyword with a matching method signature.

Assign methods to delegates only if their signatures match exactly.

Always check if a delegate is null before invoking it to avoid runtime errors.

Use delegates to pass methods as parameters or store them as variables.

For event handling, combine delegates with the event keyword for safety.