NP114 Moving delagate type

Now program is executing. Thank you for your effort Satish Kumar Kathi

Change the access level of the MeltdownEventArgs class to public

as

public class MeltdownEventArgs : EventArgs

I am using Microsoft Visual C# 2008 Express Edition. When I tried to execute your code following error message is coming I don’t know why.

Inconsistent accessibility: parameter type 'MeltdownEventArgs' is less accessible than delegate 'MeltdownHandler'

Following code is working perfectly

public delegate void MeltdownHandler(object reactor, MeltdownEventArgs myMEA);

class MeltdownEventArgs : EventArgs

// declare a private field named message

private string message;

// define a constructor

public MeltdownEventArgs(string message)

this.message = message;

// define a property to get the message

public string Message

get

return message;

class Reactor

// declare a private field named temperature

private int temperature;

// declare a delegate class named MeltdownHandler

//public delegate void MeltdownHandler(object reactor, MeltdownEventArgs myMEA);

// declare an event named OnMeltdown

public event MeltdownHandler OnMeltdown;

// define a property to set the temperature

public int Temperature

set

temperature = value;

// if the temperature is too high, the reactor melts down

if (temperature > 1000)

MeltdownEventArgs myMEA =

new MeltdownEventArgs("Reactor meltdown in progress!");

OnMeltdown(this, myMEA);

class ReactorMonitor

// define a constructor

public ReactorMonitor(Reactor myReactor)

myReactor.OnMeltdown += new MeltdownHandler(DisplayMessage);

// define the DisplayMessage() method

public void DisplayMessage(object myReactor, MeltdownEventArgs myMEA)

Console.WriteLine(myMEA.Message);

public class Example12_4

public static void Main()

// create a Reactor object

Reactor myReactor = new Reactor();

// create a ReactorMonitor object

ReactorMonitor myReactorMonitor = new ReactorMonitor(myReactor);

// set myReactor.Temperature to 100 degrees Centigrade

Console.WriteLine("Setting reactor temperature to 100 degrees Centigrade");

// set myReactor.Temperature to 500 degrees Centigrade

Console.WriteLine("Setting reactor temperature to 500 degrees Centigrade");

// set myReactor.Temperature to 2000 degrees Centigrade

// (this causes the reactor to meltdown)

Console.WriteLine("Setting reactor temperature to 2000 degrees Centigrade");

In the first example you have declared the delegate with in the class and calling with classname.delegatename

When you moved out the delegate out of the class you have not removed the class name when you are calling the delegate

Replace following line with

myReactor.OnMeltdown += new Reactor.MeltdownHandler(DisplayMessage);// looking for delegate MeltdownHandler in Reactor class, which is not existing

with

myReactor.OnMeltdown += new MeltdownHandler(DisplayMessage);

this will work

same as the second example

bookShop.AddBook += new

              AddBookEventHandler(notify.instance_AddBook);

Hope this helps

In the following program delagate type is declared outside the class but program is executing well. What is the reason.   

using System;

using System.Collections;

    public delegate void AddBookEventHandler(object source, BookEventArgs e);

    public class Book

    {

        private string title;

        private string isbn;

        private decimal price;

        public Book(string title, string isbn, decimal price)

        {

            this.title = title;

            this.isbn = isbn;

            this.price = price;

        }

        public string Title

        {

            get { return this.title; }

        }

        public string ISBN

        {

            get { return this.isbn; }

        }

        public decimal Price

        {

            get { return this.price; }

        }

    }

    public class BookShop

    {

        private ArrayList books;

        private string name;

        public event AddBookEventHandler AddBook;

        public BookShop(string name)

        {

            books = new ArrayList();

            this.name = name;

        }

        protected void OnAddBook(BookEventArgs e)

        {

            if (AddBook != null)

                AddBook(this, e);

        }

        public void AddNewBook(Book book)

        {

            this.books.Add(book);

            BookEventArgs e = new BookEventArgs(book);

            OnAddBook(e);

        }

    }

    public class BookEventArgs : EventArgs

    {

        private Book book;

        public BookEventArgs(Book book)

        {

            this.book = book;

        }

        public Book Book

        {

            get { return this.book; }

        }

    }

    public class Notifier

    {

        public void instance_AddBook(object source, BookEventArgs e)

        {

            Console.WriteLine("A Message has been sent to the Members\n" + " regarding the book '{0}' with the ISBN '{1}'\n", e.Book.Title, e.Book.ISBN);

        }

    }

    //The Sys Class is the application that uses all the above classes.

    //Let's look at the code:

    public class Sys

    {

        public static void Main()

        {

            BookShop bookShop = new BookShop(".NET Bookshop");

            Book b1 = new Book("The Right Way", "123456789", 19.90m);

            Book b2 = new Book("The .NET Stuff", "987654321", 29.90m);

            Notifier notify = new Notifier();

            bookShop.AddBook += new

              AddBookEventHandler(notify.instance_AddBook);

            bookShop.AddNewBook(b1);

            bookShop.AddNewBook(b2);

            Console.ReadLine();

        }

    }

/*

A Message has been sent to the Members

 regarding the book 'The Right Way' with the ISBN '123456789'

A Message has been sent to the Members

 regarding the book 'The .NET Stuff' with the ISBN '987654321'

*/