Geek Answers Handbook

Events without delegate type

I implemented a class similar to this interface:

[ImmutableObject(true)]
public interface ICustomEvent
{
    void Invoke(object sender, EventArgs e);

    ICustomEvent Combine(EventHandler handler);
    ICustomEvent Remove(EventHandler handler);

    ICustomEvent Combine(ICustomEvent other);
    ICustomEvent Remove(ICustomEvent other);
}

This CustomEvent class works the same as MulticastDelegate. It can be called. It can be combined with another CustomEvent. And CustomEvent can be removed from another CustomEvent.

Now I want to declare the class as follows:

class EventProvider
{
    public event CustomEvent MyEvent;

    private void OnMyEvent()
    {
        var myEvent = this.MyEvent;
        if (myEvent != null) myEvent.Invoke(this, EventArgs.Empty);
    }
}

Unfortunately, this code does not compile. The compiler error CS0066 will appear:

"EventProvider.MyEvent": the event must be a delegate type

Basically, I need a property in which there is add and remove , and not get and set , I think the only way to use this keyword is event . I know that one obvious alternative is to declare two methods that will add and remove, but I also want to avoid this.

Does anyone know if there is a good solution to this problem? I wonder if there is a way to trick the compiler to accept a type without a delegate as an event. Custom attribute, possibly.

By the way, someone asked a similar question at expert-exchange.com. Since this site is not free, I do not see the answers. Here is the topic: http://www.experts-exchange.com/Programming/Languages/C_Sharp/Q_21697455.html
+5
4

CustomEvent ( ), :

ICustomEvent EventHandler ( - ), ICustomEvent (, Invoke), Target , ICustomEvent add remove accessors.

: :

CustomEvent myEvent;
public event EventHandler MyEvent {
    add {
        if (value == null) throw new ArgumentNullException("value");
        var customHandler = value.Target as ICustomEvent;

        if (customHandler != null)
            myEvent = myEvent.Combine(customHandler);
        else
            myEvent = myEvent.Combine(value);   //An ordinary delegate
    }
    remove {
        //Similar code
    }
}

, , , ( myEvent null)

writeable CustomEvent, + -, += -= .

. , CustomEvent ( , ),

if (myEvent.Previous != value && value.Previous != myEvent)
    throw new ArgumentException("You cannot reset a CustomEvent", "value");

, value myEvent.Previous null.

+2

:

CustomEvent myEvent

public event EventHandler MyEvent {
    add { myEvent = myEvent.Combine(value); }
    remove {myEvent = myEvent.Remove(value); }
}

EventHandler, add remove.

EDIT. .
2 nd EDIT: .

+5

, / ?

" " ( ), .

+1

"+ =" "- =" CustomEvent? "+ =" "- =" , "+" "-".

, + =, , +, .

http://msdn.microsoft.com/en-us/library/8edha89s(VS.90).aspx

Therefore, instead of having add and delete methods similar to events, you might have a field or property that can be combined with the + = and - = operators. In addition, it encapsulates the combination logic inside your own CustomEvent class.

Carlos Lot.

0
source

More articles:


All Articles