C# Snippet Tutorial - Custom Event Handlers

Very nice and simple, good stuff

This is a nice example of how to generate an event, but I'd like to find a nice example of how the event can be useful.

Thanks man! This is exactly the thing I was looking for...

Very nice, a simple code with works

Very nice, this is just what i needed to get around the limitations of multi-threading!

good tutorial and example on how to create new event.

Really very nice and simple.My confusion abt events and delegates cleared now.Good Service. Thank you very much

Extremely useful. Thanks a lot

Very clear and useful. Cleared up events for me perfectly.

Gosh! I've been looking for something simple out there that can make me understand the creation of these events.

Great tutorial! You're a life saver!

What I was looking for exactly. Simple and useful. Thank you.

Thanks for a VERY clear and VERY helpful tutorial. Awesome! I have saved this in my bookmarks of very helpful webpages.

Finally found what i have bbeen looking for , for ages. never found anything as simple and straighforward as this - so beautifully explaining events and basic delagates.

Thanks for taking the time to write this up. Nice job on showing how the code works by modifying the same code over and over till you get to the end. This topic is too complex to show one big snippet of code and try to explain it all. The car idea made for a good tutorial as well. Better than the New News example I was trying to follow.

I confirm, such explanation is rare. You don't go directly to the final solution but explain the reason of each element separately step-by-step.

Great Job. thanks

nice

excellent mate. very good for new learner.

Thank you, I appreciate the simplicity!

Excellent, just what I needed. Thanks!

Thanks. It's worth to say that your effort was so great. Thanks a lot. Looking forward your new posts.

I still have a bit of problem understanding this fully. I get what you are telling but let's say I want to set one of the other fields when the OwnerChanged event is fired. Maybe I need to set a different licenseplate when the owner has changed.

How would I do that?

Excellent!!!! Thank you.

Thanks, this was extremely clear and well presented.

what am I doing wrong I get this error (I copied and paste as it was in the article)

Error 1 The type or namespace name 'OwnerChangedEventHandler' could not be found (are you missing a using directive or an assembly reference?)

please help

This is the best explanation of custom event handlers I've ever seen. Thanks

Thanks. This is a nice explanation that helped me to understand about events.

Good work!

Beautiful example... thanks a lot..

Your tutorials are so easy to understand. Thanks

I must say this is the best tutorial on event handling I’ve seen, great!

I just love your tutorials. Very clear and concise :) Thanks again!

I have existing code that follows your tutorial. The issue I have is that the event has mutiple handlers and only one is being fired. I have stepped through the code and I add about 30 odd handlers for this event. But only one is fired.

Can you give me some ideas to look for in my code.

I am wary of events in .net, as you have rightly stated the complexities involved, in another of your article on events. I am afraid of using them, hence forget all about them, and everytime I come across a reading on delegate and events - I sit up with curiosity - as though I am reading for the first time:) To make things worse, they differ so much across C# and vb.net. Nice article, thanks!

This bit of code here:

        if (this.OwnerChanged != null)
          this.OwnerChanged(value);

Looks like it's making sure that the .OwnerChanged event is being "listened to" or wired-up. Correct?

Many thanks the real-world example explains the concept brilliantly.

Very very clear explanation. Thank you :)

?????? ?? ?????????

Hi!

I've concatenated your tutorials' examples about serialization and this one to make datagrid viewable class that can be serialized. But there's a problem. I don't know how to perform it mostly because of

 public event PropertyChangedEventHandler PropertyChanged; 

field. And there's one more question. When DataGrid is edited, we have our BindingList updated, right? But can I add some other functions that are need to be performed when something's changed in BindingList? Thank you very much in advance.

Actually,

private void openToolStripMenuItem1_Click(object sender, EventArgs e)
{
  ObjectToSerialize ots = new ObjectToSerialize();
  Serializer sr = new Serializer();
  ots = sr.DeSerializeObject("a.regress");
  precedents = ots.Precedents;

}

I debugged this code and I can say that BindingList (precedents) changes okay, but datagrid still shows things that was before this method was called.

Good Article...Thanks

This is the best explanation on the

event

topic I have seen so far! Thank you!

Wow! Best of all!

Nice simple and easy to understand article Thanks man..

wonderful article . simply explained :)

thank you so much for this clean explanation on events. It makes sense to me now.

I have small problem.

I made 4 textboxes (make, model,year and owner) and a button.

When I change a owner, event fires up correctly, however it keeps repeating it's self.

For example, I have this code:

void car_OwnerChanged(string newOwner)
        {
            MessageBox.Show("Hello, owner changed");

        }

When I change the owner, message box pops. When I change it again, message box pops 2 times (must ok it). If I do it 10 times, there will be 10 text boxes.

How do I make it pop only once?

Thank you for fast reply :)

Here is my class code:

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

namespace events
{
    public class Car
    {
        public delegate void OwnerChangedEventHandler(string newOwner);
        public event OwnerChangedEventHandler OwnerChanged;


        private string make;
        private string model;
        private int year;
        private string owner;

        public string CarMake
        {
            get { return this.make; }
            set { this.make = value; }
        }

        public string CarModel
        {
            get { return this.model; }
            set { this.model = value; }
        }

        public int CarYear
        {
            get { return this.year; }
            set { this.year = value; }
        }

        public string CarOwner
        {
            get { return this.owner; }
            set
            {
                this.owner = value;
                if (this.OwnerChanged != null)
                    this.OwnerChanged(value);
            }
        }

        public Car()
        {
        }
    }
}

And here is form code.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace events
{


    public partial class Form1 : Form
    {



        public Form1()
        {
            InitializeComponent();


        }
        Car car = new Car();


        private void button1_Click(object sender, EventArgs e)
        {


            car.OwnerChanged += new Car.OwnerChangedEventHandler(car_OwnerChanged);

            car.CarMake = textBox1.Text;
            car.CarOwner = textBox2.Text;
            car.CarModel = textBox3.Text;
            car.CarYear = Convert.ToInt32( textBox4.Text);


        }

        void car_OwnerChanged(string newOwner)
        {
            MessageBox.Show(newOwner);
            //throw new NotImplementedException();
        }

        private void button2_Click(object sender, EventArgs e)
        {

            textBox6.Text = car.CarMake; 
            textBox9.Text = car.CarOwner;
            textBox8.Text = car.CarModel;
            textBox7.Text  = Convert.ToString (car.CarYear);


        }

        private void button3_Click(object sender, EventArgs e)
        {
            textBox5.Text = car.CarOwner;
        }


        void car_OwnerChanged(object sender, EventArgs e)
        {
            MessageBox.Show("Hello from EVENT");
        }

    }
}

And again thank you so much.

I would like to thank you for your time maintaining this web site. For dedicating your free time to help us, with these tutorials that are best on the web.

Every single text here, is understandable and easy to follow. Have you thought about publishing a book?

I know that this is my first web site to check every morning.

Keep on doing great things, and as soon as I have something to publish, I will do it here :)

Great Article! Helped me a lot.

i learnt lot from this site thank u all..........

Nice explanation. Keep posting such articles.

so... an event is just a C function pointer with microsoft naming parafernalia.

Great article! Precisely written! Thank you!

I have been learning events and I am not sure why i should use events in my code, it seems events are only usefull in an object which will be reused by a third party i.e thats why microsoft have so many events in there objects because they will be used by third parties and do not know hgow those third parties want to use the object so events is a good way of giving a choice, but in code that will not be reused, i dont see any reason for using events over just a method, i.e your car example, if i know that every car will have an owner change, why put in an event over a method, if is just different types of car then why not put a method at base level, so events seem a bit off overkill if you are creating code for yourself. Is this correct.

Finally, the lesson on custom events that I have been looking for. I have never understood WHY the delegate was used before reading this and now I get it. Thanks a million!

man, this has been very helpful. thank you for the clear explanation

thanks. very nice and to the point

Great example. Simple and clean.

Surprising how long it takes other people to explain the concept of C# events! I spent a half hour surfing before I found your example and then "got it" in minutes. Thanks!

Very Nice!!!

Nice one! That's exactly what i was looking for!:) thanks

will it be posible to explain why the event handler is static in this http://msdn.microsoft.com/en-us/library/w9y9a401(v=VS.100).aspx example ?

i tryed removing the static and it does not run, even tho neither the compiler nor the CLR complains

TIA

Simple example to show custom event and event handling using System; class myarray { public int[] num=new int[5]; public delegate void sortHandler(int[] ab); //delegate defined public event sortHandler sort; //event sort is defined based on delegate sortHandler public myarray() { int i; this.sort+=new sortHandler(num_sort); //sort event is added to this class for(i=0;i

Your examples and presentation seen ALWAYS to be the clearest of all I check. Thank-you for your time and efforts!!

Nice but I don't knew About Delegates..........

nice and clean explanation

Thanks for the tutorial. Nice clear language which helped me understand it on the first read.

Another happy coder here. This is the only damn tutorial out there that could teach me event handling. Not even MSDN had a good explanation. THANK YOU!

This is best tutorial for custom event handling. Thanks..!!!!!!

Thank you!

Is Safe Thread?

public string CarOwner { get { return this.owner; } set { this.owner = value; if (this.OwnerChanged != null) // q1 this.OwnerChanged(this, new EventArgs());// q2 } }

1thread 2thread current line -> q1

1Thread q1 -> change OwnerChanged = null and.. 2Thread q2 excute...

2thread null Ownerchanged excute...

is safe thread?

Car car = new Car();

//adds an event handler to the OwnerChanged event car.OwnerChanged += new OwnerChangedEventHandler(car_OwnerChanged);

//setting this will fire the OwnerChanged event car.CarOwner = "The Reddest";

...I have some problem in this line...

car.OwnerChanged += new Car.OwnerChangedEventHandler(car_OwnerChanged);

why it use Car ..class name instead of using our created instance car....

I dun understand.. In my opinion..It should be car.OwnerChangedEventHandler(car_OwnerChanged);

please help in this confussion

This is a great article which I ever found.Thank you very much.

thank you very much for this fruitful example.

You are like angel after some hours of nothing :)

thx

keep on the good work, GOD bless u my frnd !!

Thanx, This was a very clear and instructional

Hey, Custom events well explained. Just wanted to clarify one thing. What you have done is whenever a property is changed or set, we just want to call a method. Why cant we just do a method call directly from the property's set, without having to use events? Is there something i'm missing here?

Never worked on a real usage of custom events. It would be great if you can list a few of custom events in real time projects.

Thanks

Thank you. I was reading a convoluted example in a text book, which had me scratching my head. One read through your tutorial was all that was required and no head scratching :-) Very clear. Thanks again.

Hello for some reason this line of code is cannot be recognised by my IDE. Could you please help

car.OwnerChanged += new OwnerChangedEventHandler(OwnerChangedHandler);

Error message= Error 1 The type or namespace name 'OwnerChangedEventHandler' could not be found (are you missing a using directive or an assembly reference?) C:\Users\Pawan\AppData\Local\Temporary Projects\WindowsFormsApplication1\Form1.cs 19 37 WindowsFormsApplication1

Here's the full Code

    public class Car
    {
        //Declare the delegate
        public delegate void OwnerChangedEventHandler(string newOwner);
        //Declare the event 
        public  event OwnerChangedEventHandler OwnerChanged;

        private string _carOwner = "Nathan";
        public string CarMake
        {
            get;
            set;
        }

        public string CarModel
        {
            get;
            set;
        }

        public int CarYear
        {
            get;
            set;
        }

        public string CarOwner
        {
            get { return _carOwner; }
            set
            {
                _carOwner = value;
                if (this.OwnerChanged != null)
                {
                    this.OwnerChanged(value);
                }
            }
        }

    }//end of class Car



 public partial class Form1 : Form
    {
        public Form1()
        {

            Car car = new Car();     
            car.OwnerChanged += new OwnerChangedEventHandler(OwnerChangedHandler);
            MessageBox.Show("Cars owner name is " + car.CarOwner);
            car.CarOwner = "Rookie";        
        }

        void OwnerChangedHandler(object sender, EventArgs arg)
        {
            Console.WriteLine("Cars Owner has been changed");
        }

    }

Really helpful.....

Thanks a lot for this useful article.

public partial class MyUserControl : System.Web.UI.UserControl { public delegate void Handler1(object sender, EventArgs e); public static event Handler1 CountrySelectedIndexChange; public static event Handler1 StateSelectedIndexChange; public static event Handler1 btnUploadClick; public static event Handler1 btnSubmitClick; public static event Handler1 btnCancelClick; protected void Page_Load(object sender, EventArgs e) { if (!Page.IsPostBack) { clsCountry_Master objCountry = new clsCountry_Master(); DataTable dtCounry = objCountry.GetAllCountry_Master(); objCountry.FillFilteredRADComboList(rcbCountryName, dtCounry); } } protected virtual void rcbCountryName_SelectedIndexChanged(object sender, Telerik.Web.UI.RadComboBoxSelectedIndexChangedEventArgs e) {

string CounryName = rcbCountryName.Text; if (rcbCountryName.Text != null) { CountrySelectedIndexChange(this, e); } } protected void rcbStateName_SelectedIndexChanged(object sender, Telerik.Web.UI.RadComboBoxSelectedIndexChangedEventArgs e) { if (StateSelectedIndexChange != null) { StateSelectedIndexChange(this,e); } } protected void btnUpload_Click(object sender, EventArgs e) { if (btnUploadClick != null) { btnUploadClick(this, e); } } protected void btnSubmit_Click(object sender, EventArgs e) { if (btnSubmitClick != null) { btnSubmitClick(this, e); } } protected void btnCancel_Click(object sender, EventArgs e) { if (btnCancelClick != null) { btnCancelClick(this, e); } }

public string SelectedCountryValue { get { return rcbCountryName.SelectedValue; } set { rcbCountryName.SelectedValue = value; } } } ***************** this is my ascx.cs file.I am getting NULL Value for every event. So please help me.

PLEASE SEND YOUR ANSWERS TO cbgbala@gmail.com

Please Help Me............

I registered an account just to comment this is the best explanation of custom events I have ever read. You should write a book. Thanks so much!

-d