EventHandler type with no event args

When we want to pass data to an event subscriber, we use EventArgs (or CustomEventArgs) for this.

.Net provides a build in type EventHandler that uses as a parameter an instance of EventArgs class that is build in as well.

What about cases, when I need to notify a subscriber that some action is over, for example search is over? I don't want to even use EventArgs, that won't contain anything.

Is there a build in type for signaling another class, without开发者_如何学C the need to use empty EventArgs?

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I really would advise you to use the standard EventHandler pattern here and just pass EventArgs.Empty. However, you can use Action as an event type if you really want – it is just unusual.

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You have several options:

1. Use a normal event with an EventHandler and the basic EventArg class – sure the event is empty, but does this do any harm?
2. Make your own delegate and use this with event MyDelegateWithoutParams MyEvent;
3. Use the Observer Pattern with IObservable instead.
4. Let clients pass an Action to you and call this action.

I hope one of these options is to your liking. I use 1 and 4 for this kind of situation (4 mostly, if there will be only one "listener").

PS: I guess 2 won't conform to the .NET framework guidelines, so maybe that one is not the best idea ;)

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if you use plain delegates surely you can do what you want but if you use events I think the best is to stick on the standard and always have object sender and EventArgs e.

if you really do not know what to pass on firing those events from your own code, just pass EventArgs.Empty as second parameter.

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Use Actions (below answer copied from https://stackoverflow.com/a/1689341/1288473):

Declaring:

public event Action EventWithoutParams; 
public event Action<int> EventWithIntParam;

Calling:

EventWithoutParams?.Invoke(); 
EventWithIntParam?.Invoke(123);