Delegates Vs Class

The difference is that the delegate calls the method indirectly rather than directly. This is achieved by adding the method to the delegate's invocation list and then calling its Invoke method, though C# has special syntax for both these steps.

The disadvantage of delegates is that an indirect call is slower than a direct call and needs more code.

The main advantages are that:

1 . More than one method can be called via a single delegate invocation.

2. A delegate enables method pointers to be passed to other methods so they can be called back from there.

3. Delegates are the basis of events in .NET.

The following simple example illustrates these points:

using System;

delegate void Del();

class MyClass

{

public event Del MyDel;

public void A()

{

Console.WriteLine("Hello from A");

}

public void B()

{

Console.WriteLine("Hello from B");

}

public void Fire()

{

if (MyDel != null) MyDel();

}

class Program

{

static void Main()

{

MyClass mc = new MyClass();

Del del = mc.A;

del += mc.B; // add a second method to delegate's invocation list

MyMethod(del); // pass delegate to a method

del -= mc.A; // remove 1st method from invocation list

del -= mc.B; // remove 2nd method

mc.MyDel += Handler; // add handler for MyDel event

mc.Fire(); // fire event

Console.ReadKey();

}

static void MyMethod(Del del)

{

del(); // call both methods one after the other

}

static void Handler()

{

Console.WriteLine("Hello from Handler");

}

The output is:

Hello from A

Hello from B

Hello from Handler

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Vulpes13y ago
The difference is that the delegate calls the method indirectly rather than directly. This is achieved by adding the method to the delegate's invocation list and then calling its Invoke method, though C# has special syntax for both these steps.

The disadvantage of delegates is that an indirect call is slower than a direct call and needs more code.

The main advantages are that:

1 . More than one method can be called via a single delegate invocation.

2. A delegate enables method pointers to be passed to other methods so they can be called back from there.

3. Delegates are the basis of events in .NET.

The following simple example illustrates these points:

using System;

delegate void Del();

class MyClass
{
public event Del MyDel;

public void A()
{
Console.WriteLine("Hello from A");
}

public void B()
{
Console.WriteLine("Hello from B");
}

public void Fire()
{
if (MyDel != null) MyDel();
}
}

class Program
{
static void Main()
{
MyClass mc = new MyClass();
Del del = mc.A;
del += mc.B; // add a second method to delegate's invocation list
MyMethod(del); // pass delegate to a method
del -= mc.A; // remove 1st method from invocation list
del -= mc.B; // remove 2nd method

mc.MyDel += Handler; // add handler for MyDel event
mc.Fire(); // fire event
Console.ReadKey();
}

static void MyMethod(Del del)
{
del(); // call both methods one after the other
}

static void Handler()
{
Console.WriteLine("Hello from Handler");
}
}

The output is:

Hello from A
Hello from B
Hello from Handler