使用数组初始化List

Question

我想在编译时填充字符串数组的List

这样的事情:

        List<string[]> synonyms = new List<string[]> 
        {
            { "enabled", "enable", "enabling" },
            { "disabled", "disable", "disabling" },
            { "s0", "s0 state" },
            { "s5", "s5 state" }
        };

但我得到一个编译错误: No overloaded method 'Add' takes 2 arguments

为什么是这样？如果它们不是字符串数组,它就可以工作List<string>

Answer 1

您没有在示例中创建数组,请尝试以下操作:

    List<string[]> synonyms = new List<string[]> 
    {
        new[] { "enabled", "enable", "enabling" },
        new[] { "disabled", "disable", "disabling" },
        new[] { "s0", "s0 state" },
        new[] { "s5", "s5 state" }
    };

Answer 2

您需要添加一个字符串数组

List<string[]> synonyms = new List<string[]> 
    {
        new string[] { "enabled", "enable", "enabling" },
        new string[] { "disabled", "disable", "disabling" },
        new string[] { "s0", "s0 state" },
        new string[] { "s5", "s5 state" } 
    };

Answer 3

为List初始化程序创建隐式类型数组:

List<string[]> synonyms = new List<string[]> 
{
    new [] { "enabled", "enable", "enabling" },
    new [] { "disabled", "disable", "disabling" },
    new [] { "s0", "s0 state" },
    new [] { "s5", "s5 state" }
};

new [] { ... }相当于new string[] { ... }当数组中的对象类型都是时string.如果数组中对象的类型不同,您将使用隐式语法获得错误.

Answer 4

究其原因,你的代码并没有工作在阐述了如何:初始化字典与集合初始化器(C#编程指南):

字典包含键/值对的集合.它的Add方法有两个参数,一个用于键,一个用于值.要初始化Dictionary 或Add方法采用多个参数的任何集合,请将每组参数括在大括号中...

因此,在语法中

    {
        { "enabled", "enable", "enabling" },
    }

编译器期望您的集合有一个Add(string, string, string)方法.因为没有这样的方法List<string []>,所以编译失败.

实际上,可以使用这种语法创建这样的集合并对其进行初始化.如果您创建以下集合:

public class TripleCollection<T> : IEnumerable<Tuple<T, T, T>>
{
    readonly List<Tuple<T, T, T>> list = new List<Tuple<T, T, T>>();

    public void Add(T first, T second, T third)
    {
        list.Add(Tuple.Create(first, second, third));
    }

    public IEnumerator<Tuple<T, T, T>> GetEnumerator()
    {
        return list.GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

以下将成功编译并创建一个包含一个3元组的集合:

        var tuples = new TripleCollection<string>
        {
            { "1", "2", "3" },
        };

您还可以创建以下List子类:

public class ListOfArray<T> : List<T[]>
{
    public new void Add(params T[] args)
    {
        base.Add(args);
    }
}

并使用所需的语法初始化它:

        var synonyms = new ListOfArray<string>
        {
            { "enabled", "enable", "enabling" },
            { "disabled", "disable", "disabling" },
            { "s0", "s0 state" },
            { "s5", "s5 state" }
        };

但List<string []>正如其他人所指出的那样,您需要通过显式分配每个string []条目来初始化您的同义词列表,而不是为每个条目使用隐式集合intializer:

        var synonyms = new List<string[]>
        {
            new [] { "enabled", "enable", "enabling" },
            new [] { "disabled", "disable", "disabling" },
            new [] { "s0", "s0 state" },
            new [] { "s5", "s5 state" }
        };

Answer 5

您需要指定内部对象是数组,以便它不会查找多参数Add方法.

    List<string[]> synonyms = new List<string[]> 
    {
        new[] { "enabled", "enable", "enabling" },
        new[] { "disabled", "disable", "disabling" },
        new[] { "s0", "s0 state" },
        new[] { "s5", "s5 state" }
    };