Is it safe to unsubscribe from an event that has never been subscribed?

Question

For example, if these codes:

        Button button1 = new Button();
        // ...
        button1.Click -= button1_Clicked;

are executed before:

        button1.Click += button1_Clicked;

I found no error or exception, but I am wondering if there is any downside here.

If it is safe, why is it allowed to unsubscribe from an event that has never been subscribed?

It does not really make sense to me that we could unsubscribe from something before we subscribe to it first. — Setyo N, Sep 05 '14 at 03:35
Fair enough, but consider a `List`. If you call `list.Remove(new T())`, it won't throw an exception. At most, you'll get a return value of `false` from most C# collection types. — Matthew Haugen, Sep 05 '14 at 03:43

score 16 · Accepted Answer · answered Sep 05 '14 at 03:35

16

I can't find a reference specific to events, but it is documented for the underlying function that events use, Delegate.Remove:

Returns source if value is null or if the invocation list of value is not found within the invocation list of source

So it will be safe at least for events that use implicit accessors.

Custom accessors are a whole other ball of wax, as one could implement the remove block however you want. I would assume people would mimic the implicit behavior, but this isn't enforced.

answered Sep 05 '14 at 03:35

Cory Nelson

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Where could I find this reference? – Setyo N Sep 05 '14 at 03:37
2

MSDN documents [Delegate.Remove](http://msdn.microsoft.com/en-us/library/system.delegate.remove.aspx) – Cory Nelson Sep 05 '14 at 03:40

Is it safe to unsubscribe from an event that has never been subscribed?

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