In C#, how can a closure reference itself?

Question

In C#, how can a closure reference itself? The use case is to automatically unsubscribe from an event, after a single occurrence (or on some condition). I know you can create an instance of a delegate, but I'd really like to keep this as a closure, to maintain context. For example:

var someVar = new FooBar();
textBox1.TextChanged += (s, e) => {
    doSomething(someVar);
    // Unsubscribe from further events
    // textBox1.TextChanged -= myself?
    // If I don't unsubscribe, I'm needlessly keeping reference
    // to someVar, and I don't intend to keep triggering this code
    // upon further events.
};

I believe you'll have to actually put `doSomething` in an actual event, as you cannot remove the subscription with this; `textBox1.TextChanged = null`. So you'll need an actual method / event to remove. — sab669, Nov 12 '15 at 19:21

score 1 · Accepted Answer · edited May 23 '17 at 11:59

1

As far as I know it cannot reference itself directly. However, you do something like this instead:

var someVar = new FooBar();
EventHandler closure = null;
closure = (s, e) => {
    doSomething(someVar);
    // Unsubscribe from further events
    // textBox1.TextChanged -= myself?
    // If I don't unsubscribe, I'm needlessly keeping reference
    // to someVar, and I don't intend to keep triggering this code
    // upon further events.
    textBox1.TextChanged -= closure;
};
textBox1.TextChanged += closure;

Credit: Can an anonymous method in C# call itself?

edited May 23 '17 at 11:59

Community

1
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answered Nov 12 '15 at 19:29

rmblstrp

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That probably should be `Action – juharr Nov 12 '15 at 19:33
Actually, the type should be simply `EventHandler` – Yacoub Massad Nov 12 '15 at 19:33
Or `TextChangedEventHandler` – juharr Nov 12 '15 at 19:34
Good point. I was showing the rough idea, however I will make the appropriate edit so it is more accurate. – rmblstrp Nov 12 '15 at 19:42
Seems that TextChangedEventHandler is defined in the PresentationFramework assembly. For this example I will just assume WinForms or maybe even WebForms. https://msdn.microsoft.com/en-us/library/system.windows.controls.textchangedeventhandler(v=vs.110).aspx – rmblstrp Nov 12 '15 at 19:53

In C#, how can a closure reference itself?

1 Answers1