C#中Dictionary的初始化方式

本文翻译自：Proper way to initialize a C# dictionary with values?

I am creating a dictionary in a C# file with the following code: 我正在使用以下代码在C＃文件中创建字典：

private readonly Dictionary<string, XlFileFormat> FILE_TYPE_DICT
        = new Dictionary<string, XlFileFormat>
        {
            {"csv", XlFileFormat.xlCSV},
            {"html", XlFileFormat.xlHtml}
        };

There is a red line under new with the error: new错误下面有一条红线：

Feature ‘collection initilializer‘ cannot be used because it is not part of the ISO-2 C# language specification 无法使用功能‘集合initilializer‘，因为它不是ISO-2 C＃语言规范的一部分

Can anyone explain what is going on here? 谁能解释一下这里发生了什么？

EDIT: okay, so it turns out I was using .NET version 2. 编辑：好的，所以事实证明我使用的是.NET版本2。

#1楼

参考：https://stackoom.com/question/19WrK/使用值初始化C-字典的正确方法

#2楼

I can‘t reproduce this issue in a simple .NET 4.0 console application: 我无法在简单的.NET 4.0控制台应用程序中重现此问题：

static class Program
{
    static void Main(string[] args)
    {
        var myDict = new Dictionary<string, string>
        {
            { "key1", "value1" },
            { "key2", "value2" }
        };
 
        Console.ReadKey();
    }
}

Can you try to reproduce it in a simple Console application and go from there? 您可以尝试在简单的控制台应用程序中重现它并从那里开始吗？ It seems likely that you‘re targeting .NET 2.0 (which doesn‘t support it) or client profile framework, rather than a version of .NET that supports initialization syntax. 您似乎可能是针对.NET 2.0（不支持它）或客户端配置文件框架，而不是支持初始化语法的.NET版本。

#3楼

Object initializers were introduced in C# 3.0, check which framework version you are targeting. 在C＃3.0中引入了对象初始化程序，检查您要定位的框架版本。

Overview of C# 3.0 C＃3.0概述

#4楼

With C# 6.0, you can create a dictionary in following way: 使用C＃6.0，您可以通过以下方式创建字典：

var dict = new Dictionary<string, int>
{
    ["one"] = 1,
    ["two"] = 2,
    ["three"] = 3
};

It even works with custom types. 它甚至适用于自定义类型。

#5楼

You can initialize a Dictionary (and other collections) inline. 您可以内联初始化Dictionary （和其他集合）。 Each member is contained with braces: 每个成员都包含大括号：

Dictionary<int, StudentName> students = new Dictionary<int, StudentName>
{
    { 111, new StudentName { FirstName = "Sachin", LastName = "Karnik", ID = 211 } },
    { 112, new StudentName { FirstName = "Dina", LastName = "Salimzianova", ID = 317 } },
    { 113, new StudentName { FirstName = "Andy", LastName = "Ruth", ID = 198 } }
};

See MSDN for details. 有关详细信息，请参阅MSDN

#6楼

Suppose we have a dictionary like this 假设我们有这样的字典

Dictionary<int,string> dict = new Dictionary<int, string>();
dict.Add(1, "Mohan");
dict.Add(2, "Kishor");
dict.Add(3, "Pankaj");
dict.Add(4, "Jeetu");

We can initialize it as follow. 我们可以按如下方式初始化它。

Dictionary<int, string> dict = new Dictionary<int, string>  
{
    { 1, "Mohan" },
    { 2, "Kishor" },
    { 3, "Pankaj" },
    { 4, "Jeetu" }
};