one handler for many instance

I have 2 instances from one class.

Rectangle first = new Rectangle();
OnErrorHandler handler = new OnErrorHandler(Rectangle_OnError);
first.OnError += handler;
second.OnError += handler;

first.Width = 10;
first.Height = -5;

second.Width = -4;
second.Height = 2;

first.OnError -= handler;
first.Width = -1;
Rectangle second = new Rectangle();

and I want to know which instance creates event?

namespace EventSample
{
    public delegate void OnErrorHandler(string message);    
}

public class Rectangle
{
    public event OnErrorHandler OnError;

    private int _Width;
    private int _Height;

    public int Width
    {
        get
        {
            return _Width;
        }
        set
        {
            if (value < 0)
            {
   开发者_JAVA百科             if (OnError != null)
                    OnError("Width can not be less than zero!");

                return;
            }

            _Width = value;
        }
    }

thanks for your help.

---

As ChaosPandion said above, you should use exceptions to inform about error conditions.

Assuming that you still want to use events, you should use the proper convention for event handlers in C#. This involves using the predefined EventHandler<TEventArgs> delegate rather than creating your own delegate. The signature is this:

public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e);

The important part in this case is the sender, which by convention is the instance which raised the event. The typical way to raise the event is like this:

EventHandler<MyEventArgs> myEvent = this.MyEvent;
if (myEvent != null)
{
    // pass 'this' as sender to tell who is raising the event
    myEvent(this, new MyEventArgs(/* ... */));
}

---

You should be using exceptions for this (as Chaos mentions).

if (value < 0)
{
  throw new ArgumentException("Width can not be less than zero!");
}

see MSDN