4-3-2.C# 数据容器 - Dictionary 扩展（Dictionary 存储对象的特性、Dictionary 与数组的转换）

Dictionary 概述

1. Dictionary<TKey, TValue> 存储的是键值对（Key - Value），通过键（Key）来存储或修改值（Value）

2. Dictionary<TKey, TValue> 存储的键值对是无序的

3. Dictionary<TKey, TValue> 存储的键是不可重复的

4. Dictionary<TKey, TValue> 支持泛型，可以指定存储的键值对的类型

5. Dictionary<TKey, TValue> 不是线程安全的，在多线程环境中需要谨慎使用

一、Dictionary 存储对象的特性

1. Dictionary 存储对象或对对象进行检测时（对象作为键或值时），对于没有重写 Equals 和 GetHashCode 方法的对象可能不太方便

internal class Person
{
    public String name;
    public int age;

    public Person() { }

    public Person(string name, int age)
    {
        this.name = name;
        this.age = age;
    }
}

Dictionary<Person, string> messageDict = new Dictionary<Person, string>();

messageDict.Add(new Person("Alice", 30), "Hello World 1");
messageDict.Add(new Person("Bob", 25), "Hello World 2");

Console.WriteLine(messageDict.ContainsKey(new Person("Alice", 30)));
Console.WriteLine(messageDict.ContainsKey(new Person("Alice", 31)));

# 输出结果

False
False

Dictionary<string, Person> personDict = new Dictionary<string, Person>();

personDict.Add("Alice", new Person("Alice", 30));
personDict.Add("Bob", new Person("Bob", 25));

Console.WriteLine(personDict.ContainsValue(new Person("Alice", 30)));
Console.WriteLine(personDict.ContainsValue(new Person("Alice", 31)));

# 输出结果

False
False

2. Dictionary 存储对象或对对象进行检测时（对象作为键或值时），对于重写 Equals 和 GetHashCode 方法的对象比较方便

internal class Staff
{
    public String name;
    public int age;

    public Staff() { }

    public Staff(string name, int age)
    {
        this.name = name;
        this.age = age;
    }

    // 重写 Equals 方法
    public override bool Equals(object obj)
    {
        // 检查是否为同一个对象的引用
        if (obj == this) return true;

        // 检查对象是否为空
        if (obj == null) return false;

        // 检查类型是否相同
        if (obj.GetType() != this.GetType()) return false;

        // 将 obj 转换为 Staff 类型并进行属性比较
        Staff staff = obj as Staff;

        bool agesAreEqual = age == staff.age;
        bool namesAreEqual = name == null ? null == staff.name : name.Equals(staff.name);

        return agesAreEqual && namesAreEqual;
    }

    public override int GetHashCode()
    {
        // 使用属性生成哈希码
        int hash = 17;
        hash = hash * 23 + name?.GetHashCode() ?? 0;
        hash = hash * 23 + age.GetHashCode();
        return hash;
    }
}

Dictionary<Staff, string> messageDict = new Dictionary<Staff, string>();

messageDict.Add(new Staff("Alice", 30), "Hello World 1");
messageDict.Add(new Staff("Bob", 25), "Hello World 2");

Console.WriteLine(messageDict.ContainsKey(new Staff("Alice", 30)));
Console.WriteLine(messageDict.ContainsKey(new Staff("Alice", 31)));

# 输出结果

True
False

Dictionary<string, Staff> staffDict = new Dictionary<string, Staff>();

staffDict.Add("Alice", new Staff("Alice", 30));
staffDict.Add("Bob", new Staff("Bob", 25));

Console.WriteLine(staffDict.ContainsValue(new Staff("Alice", 30)));
Console.WriteLine(staffDict.ContainsValue(new Staff("Alice", 31)));

# 输出结果

True
False

二、Dictionary 与数组的转换

1、Dictionary 转数组

1. Dictionary 转键值对数组

Dictionary<string, int> dict = new Dictionary<string, int>();

dict.Add("Alice", 30);
dict.Add("Bob", 25);

KeyValuePair<string, int>[] array = dict.ToArray();

foreach (KeyValuePair<string, int> kvp in array)
{
    Console.WriteLine($"{kvp.Key} - {kvp.Value}");
}

# 输出结果

Alice - 30
Bob - 25

2. Dictionary 转键数组

Dictionary<string, int> dict = new Dictionary<string, int>();

dict.Add("Alice", 30);
dict.Add("Bob", 25);

KeyValuePair<string, int>[] array = dict.ToArray();

foreach (KeyValuePair<string, int> kvp in array)
{
    Console.WriteLine($"{kvp.Key} - {kvp.Value}");
}

# 输出结果

Alice
Bob

3. Dictionary 转值数组

Dictionary<string, int> dict = new Dictionary<string, int>();

dict.Add("Alice", 30);
dict.Add("Bob", 25);

string[] array = dict.Keys.ToArray();

foreach (string item in array)
{
    Console.WriteLine(item);
}

# 输出结果

30
25

2、数组转 Dictionary

var array = new (string, int)[]
{
    ("Alice", 30),
    ("Bob", 25)
};

Dictionary<string, int> dict = array.ToDictionary(kvp => kvp.Item1, kvp => kvp.Item2);


foreach (KeyValuePair<string, int> kvp in dict)
{
    Console.WriteLine($"{kvp.Key} - {kvp.Value}");
}

# 输出结果

Alice - 30
Bob - 25