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Delegate in C#

Posted on 2016-09-11
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Last Modified: 2016-09-13
Hi guys,

I just studied Delegate and understand that it encapsulate methods in "Invocation List".
And all the methods inside the invocation list will be called one by one.

My question is when do you use Delegate in real life scenarios?
I know that thread uses delegate. But beside that I heard that it's heavily used in Events.
Can you please show me actual "simple" examples that use delegate in a real life ?

Thanks~
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Question by:Isabell
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Expert Comment

by:anarki_jimbel
ID: 41793549
I believe you may find these examples/tutorials quite interesting:
https://msdn.microsoft.com/en-us/library/aa288459(v=vs.71).aspx
http://csharp-station.com/Tutorial/CSharp/Lesson14

Delegates are everywhere. They are very useful if you need, e.g., change, or add, or remove event handlers at run time.
LINQ uses delegates very intensively. Comparers, etc.
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anarki_jimbel earned 2000 total points
ID: 41793563
Simple example:

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

namespace EventTesting
{
    public delegate void overdraftDelegate(object sender);

    class Program
    {
        static void Main(string[] args)
        {
            // Create three account
            Account a1 = new Account("a1", 1000, 100);
            Account a2 = new Account("a2", 1000, 100);
            Account a3 = new Account("a3", 1000, 100);
            // add a method that will handle "overdrafted" event - it's up to you what to do
            a1.Overdrafted += OverdraftHandler;
            a2.Overdrafted += OverdraftHandler;
            a3.Overdrafted += OverdraftHandler;
            //, make withdrawals and see what happens
            a1.Withdraw(1000);
            a2.Withdraw(1100);
            a3.Withdraw(1300);

            Console.ReadLine();
        }

        /// <summary>
        /// Our event handler that we are attaching to Account's event
        /// </summary>
        /// <param name="sender"></param>
        public static void OverdraftHandler(object sender)
        {
            // Cast sender to Account so that we are able to access it's properties
            Account a = (Account)sender;
            // Print info
            Console.WriteLine("Account '" + a.name + "' has overdraft!");
        }
    }


    /// <summary>
    /// Class account has name, balance and allowed overdraft.
    /// If we withdraw money - we want to know if overdraft happens.
    /// So we fire the event from the class.
    /// In the Prograsm class we add an event handler to handle this event. It simply prints the name of the account in our case.
    /// </summary>
    public class Account
    {
        public event overdraftDelegate Overdrafted;
        
        public Account(string _name, int _balance, int _allowedOverdraft)
        {
            this.name = _name;
            this.balance = _balance;
            this.allowedOverdraft = _allowedOverdraft;
        }
        public string name;

        int balance = 0;
        int allowedOverdraft = 0;

        public int Withdraw(int quantity)
        {
            int withdrawal = 0;

            if (quantity > (balance + allowedOverdraft))
            {
                withdrawal = balance + allowedOverdraft;
            }
            else
            {
                withdrawal = quantity;
            }
            balance -= withdrawal;
            if (balance < 0)
            {
                // fire event
                Overdrafted(this);
            }
            return withdrawal;
        }
    }
}

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Author Closing Comment

by:Isabell
ID: 41797067
Thanks!
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