我的扩展方法放在哪里？ [英] Where do I put my extension method?

问题描述

这里的一位资深成员给了我这段代码：

A senior member here gave me this code:

public static string Truncate(this string value, int maxChars)
{
    return value.Length <= maxChars ? value : value.Substring(0, maxChars) + " ..";
}

他说将其用作扩展方法。但是我在哪里放置这种方法呢？似乎它向.Net

He said to use it as an extension method. But where do I put this method? It looks like it adds something to .Net

推荐答案

添加了一些内容，请考虑一个名为 StringExtensions 像这样：

Consider a class named StringExtensions like so:

static class StringExtensions
{
    public static string Truncate(this string value, int maxChars)
    {
        return value.Length <= maxChars ? 
               value : 
               value.Substring(0, maxChars) + " ..";
    }
}

请确保您将此类放在任何命名空间中，您需要为该命名空间添加 using 声明。

Be sure that whatever namespace you put this class in, you include a using declaration for that namespace.

因此，举一个完整的例子：

Thus, for a full example:

StringExtensions.cs ：

namespace My.Extensions
{
    static class StringExtensions
    {
        public static string Truncate(this string value, int maxChars)
        {       
            return value.Length <= maxChars ?
                   value :
                   value.Substring(0, maxChars) + " ..";
        }
    }
}

Program.cs ：

using System;
using My.Extensions;

namespace My.Program
{
    static class Program
    {
        static void Main(string[] args)
        {
            string s = "Hello, World";
            string t = s.Truncate(5);
            Console.WriteLine(s);
            Console.WriteLine(t);
        }
    }
}

顺便说一句，不将其添加到.NET。您甚至都没有向 String 类添加新方法。而是，这是一个编译器技巧，它使静态方法位于第一个声明为 this * TypeName * * valueParameter * 的静态类中，其中 * TypeName * 是类型的名称，而 * valueParameter * 是参数的名称，可以使该名称作为实例方法出现在类型名称为 * TypeName * 的类型。那就是

By the way, you are not adding it to .NET. You are not even adding a new method to the class String. Rather, it's a compiler trick that makes static methods living in static classes with their first parameter declared as this *TypeName* *valueParameter* where *TypeName* is the name of a type, and *valueParameter* is the name of the parameter can be made to appear as an instance method on instances of the type with type name *TypeName*. That is

string t = s.Truncate(5);

由编译器翻译为

string t = StringExtensions.Truncate(s, 5);

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