Delegates using examples

Delegate is a form of type safe functional pointer. in compile time we don't know which method will be invoked. We can invoke a delegate asynchronous. Mostly it will be used in event drive programming. number of parameter, type of parameters and return type of a delegate should be match with method signature.

There are three steps in defining and using delegates:

Declaration
Instantiation
Invocation

delegate
========

Declaration:
delegate void simpledelegate();

public void simplefun()
{
......
}
Instantiation:
simpledelegate sd = new simpledelegate(simplefunc);
Invocation:
sd();

Event is based on publishing and subscribing concept.
declare an event ( in user control)
================
public delegate void RefreshTreeHandler();
public event RefreshTreeHandler refreshtree;

protected void OnRefreshTree()
{
if(refreshtree != null)
{
refreshtree();
}
}

publishing an event in usercontrol
==================================
this.OnRefreshTree();

Subscribing an event
====================
objusercontrol.refreshtree += new usercontrol.refreshtreehandler(method);

Class Sample { public void dosomething(); { MessageBox.Show("Am from dosomething method"); } } public delegate void delegate_name(); code for btn_Click { Sample obj=new Sample();// creating object for delegate with address of method. delegate_name obj2=new delegate_name(obj.dosomething); obj2(); // call delegate object. }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace multicastdelegatecustom
{
class multiDelegateSample
{
public delegate void delName(int x, int y);

public class A
{
public event delName eventName;

public void myEvent(int x, int y)
{
eventName(x, y);
Console.WriteLine("Custom Event Raised");
}

public void Add(int p, int q)
{
Console.WriteLine("Adding Method {0}", p + q);
}

public void Sub(int x, int y)
{
Console.WriteLine("Your Subtract Method {0}", p - q);

}
}

static void Main(string[] args)
{

A obj = new A();

obj.eventName+= new delName(obj.Add);

obj.eventName+= new delName(obj.Sub);

obj.myEvent(30, 10);

Console.ReadLine();

}
}
}

Delegates using examples

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