您如何使用 Func<>和行动<>在设计应用程序时? [英] How do you use Func<> and Action<> when designing applications?

问题描述

我能找到的关于 Func<> 和 Action<> 的所有示例都是简单，如下所示，您可以在下面的示例中看到它们在技术上是如何工作的，但我想在示例中使用它们来解决以前无法解决或只能以更复杂的方式解决的问题，即我知道它们是如何工作的，并且我可以看到它们简洁而强大，所以我想从更广泛的意义上了解它们解决了哪些类型的问题，以及我如何在应用程序设计中使用它们.

All the examples I can find about Func<> and Action<> are simple as in the one below where you see how they technically work but I would like to see them used in examples where they solve problems that previously could not be solved or could be solved only in a more complex way, i.e. I know how they work and I can see they are terse and powerful, so I want to understand them in a larger sense of what kinds of problems they solve and how I could use them in the design of applications.

您以何种方式(模式)使用 Func<> 和 Action<> 来解决实际问题?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace TestFunc8282
{
    class Program
    {
        static void Main(string[] args)
        {
            //func with delegate
            Func<string, string> convert = delegate(string s)
            {
                return s.ToUpper();
            };

            //func with lambda
            Func<string, string> convert2 = s => s.Substring(3, 10);

            //action
            Action<int,string> recordIt = (i,title) =>
                {
                    Console.WriteLine("--- {0}:",title);
                    Console.WriteLine("Adding five to {0}:", i);
                    Console.WriteLine(i + 5);
                };

            Console.WriteLine(convert("This is the first test."));
            Console.WriteLine(convert2("This is the second test."));
            recordIt(5, "First one");
            recordIt(3, "Second one");

            Console.ReadLine();

        }
    }
}

推荐答案

它们对于重构 switch 语句也很方便.

They're also handy for refactoring switch statements.

举以下(虽然很简单)的例子:

Take the following (albeit simple) example:

public void Move(int distance, Direction direction)
{
    switch (direction)
    {
        case Direction.Up :
            Position.Y += distance;
            break;
        case Direction.Down:
            Position.Y -= distance;
            break;
        case Direction.Left:
            Position.X -= distance;
            break;
        case Direction.Right:
            Position.X += distance;
            break;
    }
}

使用 Action 委托，您可以按如下方式重构它:

With an Action delegate, you can refactor it as follows:

static Something()
{
    _directionMap = new Dictionary<Direction, Action<Position, int>>
    {
        { Direction.Up,    (position, distance) => position.Y +=  distance },
        { Direction.Down,  (position, distance) => position.Y -=  distance },
        { Direction.Left,  (position, distance) => position.X -=  distance },
        { Direction.Right, (position, distance) => position.X +=  distance },
    };
}

public void Move(int distance, Direction direction)
{
    _directionMap[direction](this.Position, distance);
}

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