c# - Func vs. Action vs. Predicate [复制](Func vs. Action vs. Predicate [duplicate])

Question

This question already has an answer here:

(这个问题在这里已有答案：)

• Delegates: Predicate Action Func 8 answers

  (代表：Predicate Action Func 8个答案)

With real examples and their use, can someone please help me understand:

(通过实例和它们的使用，有人可以帮助我理解：)

1. When do we need Func delegate?

   (我们什么时候需要Func委托？)

2. When do we need Action delegate?

   (我们什么时候需要行动委托？)

3. When do we need Predicates delegate?

   (我们什么时候需要Predicates委托？)

  ask by InfoLearner translate from so

Answer 1

The difference between Func and Action is simply whether you want the delegate to return a value (use Func ) or not (use Action ).

(Func和Action之间的区别仅在于您是否希望委托返回值（使用Func ）或不使用（使用Action ）。)

Func is probably most commonly used in LINQ - for example in projections:

(Func可能是LINQ中最常用的 - 例如在投影中：)

 list.Select(x => x.SomeProperty)

or filtering:

(或过滤：)

 list.Where(x => x.SomeValue == someOtherValue)

or key selection:

(或关键选择：)

 list.Join(otherList, x => x.FirstKey, y => y.SecondKey, ...)

Action is more commonly used for things like List<T>.ForEach : execute the given action for each item in the list.

(Action更常用于List<T>.ForEach ：对列表中的每个项执行给定的操作。)

I use this less often than Func , although I do sometimes use the parameterless version for things like Control.BeginInvoke and Dispatcher.BeginInvoke .

(我用这个少往往比Func ，虽然我有时会使用，例如，无参数的版本Control.BeginInvoke和Dispatcher.BeginInvoke 。)

Predicate is just a special cased Func<T, bool> really, introduced before all of the Func and most of the Action delegates came along.

(Predicate只是一个特殊的套装Func<T, bool>真的，在所有Func和大多数Action代表出现之前引入。)

I suspect that if we'd already had Func and Action in their various guises, Predicate wouldn't have been introduced... although it does impart a certain meaning to the use of the delegate, whereas Func and Action are used for widely disparate purposes.

(我怀疑，如果我们已经有各种伪装的Func和Action ，那么Predicate就不会被引入......尽管它确实赋予了代表使用某种意义，而Func和Action则被广泛地使用了目的。)

Predicate is mostly used in List<T> for methods like FindAll and RemoveAll .

(Predicate主要用于List<T>用于FindAll和RemoveAll等方法。)