CODEWITHSUNDEEP
c#events
whytheq
whytheq

Reputation: 35557

Creating a Custom Event

Can a custom event be created for any object method?
To do this do I just use the following syntax?:

myObject.myMethod +=new EventHandler(myNameEvent);

The following code has prompted this question:

   private void btRunProcessAndRefresh_Click(object sender,EventArgs e)
    {
        myProcess =new Process();
        myProcess.StartInfo.FileName = @"c:\ConsoleApplication4.exe";
        myProcess.Exited += new EventHandler(MyProcessExited);
        myProcess.EnableRaisingEvents =true;
        myProcess.SynchronizingObject =this;
        btRunProcessAndRefresh.Enabled =false;
        myProcess.Start();
    }

Upvotes: 37

Views: 151260

Answers (6)

Antoine C.
Antoine C.

Reputation: 3952

Based on @ionden's answer, the call to the delegate could be simplified using null propagation since C# 6.0.

Your code would simply be:

class MyClass {
    public event EventHandler MyEvent;

    public void Method() {
        MyEvent?.Invoke(this, EventArgs.Empty);
    }
}

Use it like this:

MyClass myObject = new MyClass();
myObject.MyEvent += myObject_MyEvent;
myObject.Method();

Upvotes: 8

Strillo
Strillo

Reputation: 2972

Yes, provided you have access to the object definition and can modify it to declare the custom event

public event EventHandler<EventArgs> ModelChanged;

And normally you'd back this up with a private method used internally to invoke the event:

private void OnModelChanged(EventArgs e)
{
    if (ModelChanged != null)
        ModelChanged(this, e);
}

Your code simply declares a handler for the declared myMethod event (you can also remove the constructor), which would get invoked every time the object triggers the event.

myObject.myMethod += myNameEvent;

Similarly, you can detach a handler using 

myObject.myMethod -= myNameEvent;

Also, you can write your own subclass of EventArgs to provide specific data when your event fires.

Upvotes: 8

Pranay Rana
Pranay Rana

Reputation: 176896

Yes you can do like this :

Creating advanced C# custom events

or

The Simplest C# Events Example Imaginable

public class Metronome
{
    public event TickHandler Tick;
    public EventArgs e = null;
    public delegate void TickHandler(Metronome m, EventArgs e);
    public void Start()
    {
        while (true)
        {
            System.Threading.Thread.Sleep(3000);
            if (Tick != null)
            {
                Tick(this, e);
            }
        }
    }
}
public class Listener
{
    public void Subscribe(Metronome m)
    {
        m.Tick += new Metronome.TickHandler(HeardIt);
    }

    private void HeardIt(Metronome m, EventArgs e)
    {
        System.Console.WriteLine("HEARD IT");
    }
}
class Test
{
    static void Main()
    {
        Metronome m = new Metronome();
        Listener l = new Listener();
        l.Subscribe(m);
        m.Start();
    }
}

Upvotes: 35

daryal
daryal

Reputation: 14919

Yes you can create events on objects, here is an example;

public class Foo
{
    public delegate void MyEvent(object sender, object param);
    event MyEvent OnMyEvent;

    public Foo()
    {
        this.OnMyEvent += new MyEvent(Foo_OnMyEvent);
    }

    void Foo_OnMyEvent(object sender, object param)
    {
        if (this.OnMyEvent != null)
        {
            //do something
        }
    }



    void RaiseEvent()
    {
        object param = new object();
        this.OnMyEvent(this,param);
    }
}

Upvotes: 14

ionden
ionden

Reputation: 12776

Declare the class containing the event:

class MyClass {
    public event EventHandler MyEvent;

    public void Method() {
        OnEvent();
    }

    private void OnEvent() {
        if (MyEvent != null) {
            MyEvent(this, EventArgs.Empty);
        }
    }
}

Use it like this:

MyClass myObject = new MyClass();
myObject.MyEvent += new EventHandler(myObject_MyEvent);
myObject.Method();

Upvotes: 45

MBen
MBen

Reputation: 3996

You need to declare your event in the class from myObject :

public event EventHandler<EventArgs> myMethod; //you should name it as an event, like ObjectChanged.

then myNameEvent is the callback to handle the event, and it can be in any other class

Upvotes: 4

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