why to declare delegate with event i, I don't see the use of the keyword event?

Question

Please show me simple example why do we need it and what will happen if we didn't use it in the example with delegate. Thank you

Answer 1

Sure:

// With events...
public class Button
{
    public event EventHandler Click;
}

public void Client
{
    public void Method(Button button)
    {
        // This is all I can do...
        button.Click += SomeHandler;
    }
}


// With plain delegate fields or properties...
public class Button
{
    public EventHandler Click { get; set; }
}

public void Client
{
    public void Method(Button button)
    {
        // Who cares if someone else is already subscribed...
        button.Click = SomeHandler;

        // And let's just raise the event ourselves...
        button.Click(button, EventArgs.Empty);
    }
}

In other words, with events you've got a controlled implementation of the pub/sub pattern - separate subscribers can't interfere with each other (except perhaps by throwing an exception within their handler) and only the publisher can "publish" (call the handlers).