C# Beginner to advanced - Lesson 29 - Delegates

Delegates:

A delegate is an object that can refer to a method.

The method can be called through this reference(delegate).

Same delegate can be used to call different methods during the runtime.

The method that will be invoked by a delegate is not determined at compile time, but rather at runtime.

The method invoking at runtime is the principal advantage of a delegate.

We can use delegates with static methods and instance methods.

delegate ret-type name(parameter-list);

Once created, a delegate instance can refer to and call methods whose return type and parameter list match those

specified by the delegate declaration.

Delegates in four steps:

1. Defining the delegate

public delegate int Calculate (int value1, int value2);

1. Creating methods which will be assigned to delegate object

//a method, that will be assigned to delegate objects

//having the EXACT signature of the delegate

public int add(int value1, int value2)

{

return value1 + value2;

}

//a method, that will be assigned to delegate objects

//having the EXACT signature of the delegate

public int sub( int value1, int value2)

{

return value1 - value2;

}

1. Creating the delegate object and assigning methods to those delegate objects

//creating the class which contains the methods

//that will be assigned to delegate objects

MyClass mc = new MyClass();

//creating delegate objects and assigning appropriate methods

//having the EXACT signature of the delegate

Calculate add = new Calculate(mc.add);

Calculate sub = new Calculate(mc.sub);

1. Calling the methods via delegate objects

//using the delegate objects to call the assigned methods

Console.WriteLine("Adding two values: " + add(10, 6)); or sum=add(10,6)

Console.WriteLine("Subtracting two values: " + sub(10,4)); or diff=sub(10,6)

Unicasting and Multicasting:

Unicasting means adding and invoking only one method.

Multicasting is the ability to create an invocation list, or chain, of methods that will be automatically called when a delegate is invoked.

Use the + or += operator to add methods to the chain.

To remove a method, use – or – =.

If the delegate returns a value, then the value returned by the last method in the list becomes the return value of the entire delegate invocation.

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