Why delegates are needed in C Sharp (C#) - Visual Breakdown

Concept Flow - Why delegates are needed

Define a delegate type

↓

Create a method matching delegate signature

↓

Create delegate instance pointing to method

↓

Pass delegate as parameter or store

↓

Invoke delegate to call method indirectly

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Program reacts to method call via delegate

Delegates let you store and pass methods as variables, so you can call methods indirectly and flexibly.

Execution Sample

C Sharp (C#)

delegate void Notify(string message);

class Program {
    static void ShowMessage(string msg) {
        Console.WriteLine(msg);
    }

    static void Main() {
        Notify notify = ShowMessage;
        notify("Hello World");
    }
}

This code defines a delegate, assigns a method to it, and calls the method through the delegate.

Execution Table

Step	Action	Evaluation	Result
1	Define delegate type Notify	delegate void Notify(string)	Notify type created
2	Define method ShowMessage	void ShowMessage(string)	Method available
3	Create delegate instance notify = ShowMessage	notify points to ShowMessage	notify stores method reference
4	Invoke notify("Hello World")	Calls ShowMessage("Hello World")	Console prints: Hello World
5	End of delegate invocation	No more calls	Program continues or ends

💡 Delegate invocation completes, program ends or continues normally

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
notify	null	points to ShowMessage	invoked ShowMessage	points to ShowMessage

Key Moments - 2 Insights

Why can't we just call ShowMessage directly instead of using a delegate?

Using a delegate lets us pass the method around and call it later or from different places, as shown in step 4 where notify.Invoke calls ShowMessage indirectly.

What does it mean that notify stores a method reference?

It means notify holds the address of the ShowMessage method, so calling notify calls that method, as seen in step 3 and 4.

Visual Quiz - 3 Questions

Look at the execution table, what does the delegate variable 'notify' point to after step 3?

A It is null

B It points to the ShowMessage method

C It points to a string message

D It points to Console.WriteLine

💡 Hint

Check the 'Result' column in step 3 of the execution table

At which step does the program print 'Hello World' to the console?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Result' column for the step where Console prints output

If we did not use a delegate and called ShowMessage directly, which step would be skipped?

A Step 1 (Define delegate)

B Step 4 (Invoke delegate)

C Step 3 (Create delegate instance)

D Step 5 (End of invocation)

💡 Hint

Delegates are created in step 3, so skipping delegates means no delegate instance creation

Concept Snapshot

Delegates are types that hold references to methods.
They let you pass methods as variables.
You create a delegate instance pointing to a method.
Invoke the delegate to call the method indirectly.
Useful for flexible callbacks and event handling.

Full Transcript

Delegates in C# are like variables that can hold methods. First, you define a delegate type that matches the method signature. Then, you create a method that matches this signature. Next, you create a delegate instance and assign it to the method. When you invoke the delegate, it calls the method indirectly. This allows you to pass methods around and call them flexibly, which is why delegates are needed.