I'm fairly convinced that this isn't possible, but I'm going to ask nonetheless.
In order to make a single-shot subscription to events, I frequently find myself using this (self-invented) pattern:
EventHandler handler=null;
handler = (sender, e) =>
{
SomeEvent -= handler;
Initialize();
};
SomeEvent += handler;
It's quite a lot of boiler-plate, and it also makes Resharper whinge about modified closures. Is there a way of turning this pattern into an extension method or similar? A better way of doing it?
Ideally, I'd like something like:
SomeEvent.OneShot(handler)
It's not very easy to refactor to an extension method, because the only way you can refer to an event in C# is by subscribing (+=
) to or unsubscribing (-=
) from it (unless it's declared in the current class).
You could use the same approach as in Reactive Extensions: Observable.FromEvent
takes two delegates to subscribe to the event an unsubscribe from it. So you could do something like that:
public static class EventHelper
{
public static void SubscribeOneShot(
Action<EventHandler> subscribe,
Action<EventHandler> unsubscribe,
EventHandler handler)
{
EventHandler actualHandler = null;
actualHandler = (sender, e) =>
{
unsubscribe(actualHandler);
handler(sender, e);
};
subscribe(actualHandler);
}
}
...
Foo f = new Foo();
EventHelper.SubscribeOneShot(
handler => f.Bar += handler,
handler => f.Bar -= handler,
(sender, e) => { /* whatever */ });
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