Question

Delegates look like such a powerful language feature, but I’ve yet to find an opportunity to use them in anger (apart from in DALs I must say).

How often do you use them, and under what circumstances do you find them most useful?

Answer 1

Funcs and Actions are newish ‘types’ of delegates and I use them a lot with Linq and really other odd situations. For Linq they are nice because personally I’d rather have a descriptive name than a lambda expression:

someList.Select(item => item.Name); 

Where with a Func I can:

Func<Item, String> itemName = item => item.Name; ... someList.Select(itemName); 

It might be a line more, but there are times where I find myself repeating a certain lambda expressions a couple times in a class, so personally I think Funcs work well for that.

Another situation is a, for lack of a better term, Method Factory. Basically it is a dictionary that holds a list of Actions as the value and say an Enum as the key:

Dictionary<UserType, Action<User>> showControls; showControls = new Dictionary<UserType, Action<User>>();  showControls.Add(SomeEnum.Admin, setControlsForAdmin); showControls.Add(SomeEnum.Normal, setControlsForNormalUser); showControls.Add(SomeEnum.Unregistered, setControlsForUnregisteredUser); 

And then I have the methods themselves written out somewhere else on the page. And use would be:

showControls[user.UserType](); 

Or maybe you want to pass the method itself to another:

Action<User> neededMethod;  neededMethod = showControls[user.UserType];  SomeMethod(neededMethod); 

I’m sure there are much better uses for delegates, but these are useful.