C# 里的 KeyValuePair＜TKey, TValue＞
我们来详细讲讲 C# 里的 KeyValuePair<TKey, TValue> —— 它是键值对（key-value pair）的基础类型，在字典（Dictionary<TKey, TValue>）中非常常见。
🔹 一、概念说明
KeyValuePair<TKey, TValue> 是一个结构体，定义在命名空间：
using System.Collections.Generic;
它包含两个只读属性：
Key：键（TKey）Value：值（TValue）
🔹 二、常见用法
✅ 示例 1：创建 KeyValuePair
using System;
using System.Collections.Generic;class Program
{static void Main(){var pair = new KeyValuePair<int, string>(1, "Apple");Console.WriteLine($"Key = {pair.Key}, Value = {pair.Value}");}
}
输出：
Key = 1, Value = Apple
✅ 示例 2：遍历 Dictionary（最常见）
var dict = new Dictionary<int, string>
{{1, "Apple"},{2, "Banana"},{3, "Cherry"}
};foreach (KeyValuePair<int, string> kvp in dict)
{Console.WriteLine($"Key: {kvp.Key}, Value: {kvp.Value}");
}
输出：
Key: 1, Value: Apple
Key: 2, Value: Banana
Key: 3, Value: Cherry
💡foreach 遍历 Dictionary 时，每个元素就是一个 KeyValuePair<TKey, TValue>。
✅ 示例 3：配合 LINQ 使用
using System.Linq;var dict = new Dictionary<string, int>
{{"Tom", 80},{"Bob", 90},{"Alice", 95}
};// 按值排序
var sorted = dict.OrderByDescending(kvp => kvp.Value);foreach (var kvp in sorted)
{Console.WriteLine($"{kvp.Key} => {kvp.Value}");
}
✅ 示例 4：用 KeyValuePair 构造 Dictionary
var pairs = new List<KeyValuePair<string, int>>
{new KeyValuePair<string, int>("A", 100),new KeyValuePair<string, int>("B", 200)
};var dict = pairs.ToDictionary(p => p.Key, p => p.Value);
🔹 三、KeyValuePair vs DictionaryEntry
| 特性 | KeyValuePair<TKey, TValue> | DictionaryEntry |
|---|---|---|
| 泛型 | ✅ 是 | ❌ 否 |
| 命名空间 | System.Collections.Generic | System.Collections |
| 推荐用法 | 推荐用于 Dictionary<TKey, TValue> | 仅用于 Hashtable 等老式集合 |
🔹 四、典型场景（在项目中）
例如你要返回一组键值对应关系（例如版本号和名字）：
List<KeyValuePair<long, string>> versionList = new()
{new KeyValuePair<long, string>(1001, "V1.0"),new KeyValuePair<long, string>(1002, "V2.0"),
};
或者在循环中临时收集数据：
var results = new List<KeyValuePair<string, int>>();foreach (var user in users)
{results.Add(new KeyValuePair<string, int>(user.Name, user.Score));
}
✅ 总结
| 功能 | 示例 |
|---|---|
| 创建 | new KeyValuePair<int, string>(1, "A") |
| 获取键 | pair.Key |
| 获取值 | pair.Value |
| 遍历字典 | foreach (var kvp in dict) |
| 构建集合 | List<KeyValuePair<string,int>> |
| 转换成字典 | .ToDictionary(p => p.Key, p => p.Value) |
源码：
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.using System.ComponentModel;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Text;namespace System.Collections.Generic
{// Provides the Create factory method for KeyValuePair<TKey, TValue>.public static class KeyValuePair{// Creates a new KeyValuePair<TKey, TValue> from the given values.public static KeyValuePair<TKey, TValue> Create<TKey, TValue>(TKey key, TValue value) =>new KeyValuePair<TKey, TValue>(key, value);/// <summary>Used by KeyValuePair.ToString to reduce generic code</summary>internal static string PairToString(object? key, object? value) =>string.Create(null, stackalloc char[256], $"[{key}, {value}]");}// A KeyValuePair holds a key and a value from a dictionary.// It is used by the IEnumerable<T> implementation for both IDictionary<TKey, TValue>// and IReadOnlyDictionary<TKey, TValue>.[Serializable][TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]public readonly struct KeyValuePair<TKey, TValue>{[DebuggerBrowsable(DebuggerBrowsableState.Never)]private readonly TKey key; // Do not rename (binary serialization)[DebuggerBrowsable(DebuggerBrowsableState.Never)]private readonly TValue value; // Do not rename (binary serialization)public KeyValuePair(TKey key, TValue value){this.key = key;this.value = value;}public TKey Key => key;public TValue Value => value;public override string ToString(){return KeyValuePair.PairToString(Key, Value);}[EditorBrowsable(EditorBrowsableState.Never)]public void Deconstruct(out TKey key, out TValue value){key = Key;value = Value;}}
}
仅供学习参考，如有侵权联系我删除。