DictionaryTKey TValue

字典<TKey，TValue>是一张地图。对于给定的键，字典中可以有一个值。

using System.Collections.Generic;

var people = new Dictionary<string, int>
{
    { "John", 30 }, {"Mary", 35}, {"Jack", 40}
};

// Reading data
Console.WriteLine(people["John"]); // 30
Console.WriteLine(people["George"]); // throws KeyNotFoundException

int age;
if (people.TryGetValue("Mary", out age))
{ 
    Console.WriteLine(age); // 35
}

// Adding and changing data
people["John"] = 40;    // Overwriting values this way is ok
people.Add("John", 40); // Throws ArgumentException since "John" already exists

// Iterating through contents
foreach(KeyValuePair<string, int> person in people)
{
    Console.WriteLine("Name={0}, Age={1}", person.Key, person.Value);
}

foreach(string name in people.Keys)
{
    Console.WriteLine("Name={0}", name);
}

foreach(int age in people.Values)
{
    Console.WriteLine("Age={0}", age);
}

使用集合初始化时重复键

var people = new Dictionary<string, int>
{
    { "John", 30 }, {"Mary", 35}, {"Jack", 40}, {"Jack", 40}
}; // throws ArgumentException since "Jack" already exists