C# |字典。添加()方法

原文:https://www . geesforgeks . org/c-sharp-dictionary-add-method/

词典< TKey，TValue >。Add()方法用于向字典中添加指定的键和值。

语法:

public void Add (TKey key, TValue value);

参数:

键:是要添加的元素的键。 值:是元素添加的值。对于引用类型，该值可以为 null。

异常:

  • ArgumentNullException :如果密钥为空。
  • ArgumentException :如果字典中已经存在相同关键字的元素。

以下是说明使用字典< TKey，TValue >的程序。添加()方法:

例 1:

// C# code to add the specified key
// and value into the Dictionary
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Create a new dictionary 
        // of strings, with string keys.
        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");

        // To get count of key/value
        // pairs in myDict
        Console.WriteLine("Total key/value pairs in"+
                    " myDict are : " + myDict.Count);

        // Displaying the key/value
        // pairs in myDict
        Console.WriteLine("The key/value pairs"+
                           " in myDict are : ");

        foreach(KeyValuePair<string, string> kvp in myDict)
        {
            Console.WriteLine("Key = {0}, Value = {1}",
                              kvp.Key, kvp.Value);
        }
    }
}

Output:

Total key/value pairs in myDict are : 6
The key/value pairs in myDict are : 
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

例 2:

// C# code to add the specified 
// key and value into the Dictionary
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Create a new dictionary of 
        // strings, with string keys.
        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");

        // The Add method throws an
        // exception if the new key is
        // already in the dictionary.
        try {

            myDict.Add("Russia", "Moscow");
        }

        catch (ArgumentException) {

            Console.WriteLine("An element with Key "+
                     "= \"Russia\" already exists.");
        }
    }
}

Output:

An element with Key = "Russia" already exists.

注:

  • 键不能为空，但如果 TValue 是引用类型，则值可以为空。
  • 如果计数小于容量，此方法将接近 0(1)操作。
  • 如果容量必须增加以容纳新元素，则此方法变成 O(n)操作，其中 n 是 Count。

参考:

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