我如何使用C#泛型字典,就像在Java中使用Hashtable一样？

使用indexer或TryGetValue()方法.如果密钥不存在,则前者抛出KeyNotFoundException,后者返回false.

实际上没有直接等同于Java Hashtable get()方法.这是因为如果密钥不存在,Java的get()将返回null.

Returns the value to which the specified key is mapped,or null if this map contains no mapping for the key.

另一方面,在C#中,我们可以将键映射到空值.如果索引器或TryGetValue()表示与键关联的值为null,则表示该键未映射.它只是意味着键被映射为null.

Running Example：

using System;
using System.Collections.Generic;

public class Program
{
    private static Dictionary<String,Tile>();
    public static void Main()
    {
        // add two items to the dictionary
        tiles.Add("x",new Tile { Name = "y" });
        tiles.Add("x:null",null);

        // indexer access
        var value1 = tiles["x"];
        Console.WriteLine(value1.Name);

        // TryGetValue access
        Tile value2;
        tiles.TryGetValue("x",out value2);
        Console.WriteLine(value2.Name);

        // indexer access of a null value
        var value3 = tiles["x:null"];
        Console.WriteLine(value3 == null);

        // TryGetValue access with a null value
        Tile value4;
        tiles.TryGetValue("x:null",out value4);
        Console.WriteLine(value4 == null);

        // indexer access with the key not present
        try
        {
            var n1 = tiles["nope"];     
        }
        catch(KeyNotFoundException e)
        {
            Console.WriteLine(e.Message);
        }

        // TryGetValue access with the key not present      
        Tile n2;
        var result = tiles.TryGetValue("nope",out n2);
        Console.WriteLine(result);
        Console.WriteLine(n2 == null);
    }

    public class Tile
    {
        public string Name { get; set; }
    }
}