C# Dictionary.Item[]用法及代码示例

此属性用于获取或设置与Dictionary中的指定键关联的值。

用法:

public TValue this[TKey key] { get; set; }

在这里，key是要获取或设置的值的Key。

属性值：这是与指定键关联的值。如果找不到指定的键，则get操作将引发KeyNotFoundException，而set操作将使用指定的键创建一个新元素。

异常：

ArgumentNullException：如果键为null。
KeyNotFoundException：如果检索到属性并且键在集合中不存在。

例：

// C# code to get or set the value 
// associated with the specified key 
using System; 
using System.Collections; 
using System.Collections.Generic; 
  
class GFG { 
  
    // Driver code 
    public static void Main() 
    { 
  
        // Creating a Dictionary named myDict 
        Dictionary<string, string> myDict = new Dictionary<string, string>(); 
  
        // Adding key/value pairs in myDict 
        myDict.Add("Australia", "Canberra"); 
        myDict.Add("Belgium", "Brussels"); 
        myDict.Add("Netherlands", "Amsterdam"); 
        myDict.Add("China", "Beijing"); 
        myDict.Add("Russia", "Moscow"); 
        myDict.Add("India", "New Delhi"); 
  
        // Displaying the key/value pairs in myDict 
        foreach(KeyValuePair<string, string> k in myDict) 
        { 
            Console.WriteLine("Key = {0}, Value = {1}", 
                              k.Key, k.Value); 
        } 
  
        // Displaying the value associated 
        // with key "Russia" 
        Console.Write("\nValue associated with Russia:"); 
        Console.Write(myDict["Russia"]); 
  
        // Setting the value associated with key "Russia" 
        myDict["Russia"] = "Saint Petersburg"; 
  
        // Displaying the value associated 
        // with key "Russia" 
        Console.Write("\n\nValue associated with Russia After Setting:"); 
        Console.Write(myDict["Russia"]); 
  
        // Displaying the value associated 
        // with key "India" 
        Console.Write("\n\nValue associated with India:"); 
        Console.Write(myDict["India"]); 
  
        // Setting the value associated with key "India" 
        myDict["India"] = "Mumbai"; 
  
        // Displaying the value associated 
        // with key "India" 
        Console.Write("\n\nValue associated with India After Setting:"); 
        Console.Write(myDict["India"]); 
        Console.WriteLine("\n"); 
  
        // Displaying the key/value pairs in myDict 
        foreach(KeyValuePair<string, string> k1 in myDict) 
        { 
            Console.WriteLine("Key = {0}, Value = {1}", 
                              k1.Key, k1.Value); 
        } 
    } 
}

输出：

Key = Australia, Value = Canberra
Key = Belgium, Value = Brussels
Key = Netherlands, Value = Amsterdam
Key = China, Value = Beijing
Key = Russia, Value = Moscow
Key = India, Value = New Delhi

Value associated with Russia:Moscow

Value associated with Russia After Setting:Saint Petersburg

Value associated with India:New Delhi

Value associated with India After Setting:Mumbai

Key = Australia, Value = Canberra
Key = Belgium, Value = Brussels
Key = Netherlands, Value = Amsterdam
Key = China, Value = Beijing
Key = Russia, Value = Saint Petersburg
Key = India, Value = Mumbai

参考：

https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.item?view=netframework-4.7.2

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注：本文由纯净天空筛选整理自Kirti_Mangal大神的英文原创作品 C# | Dictionary.Item[] Property。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。