C＃|将键和值添加到OrderedDictionary集合中

OrderedDictionary.Add(Object，Object)方法用于将具有指定键和值的条目添加到具有最低可用索引的OrderedDictionary集合中。

句法：

public void Add (object key, object value);

参数：

key : The key of the entry to add.
value : The value of the entry to add. This value can be null.

例外情况：

• NotSupportedException：如果OrderedDictionary集合为只读。
• ArgumentException：如果OrderedDictionary集合中已经存在具有相同键的元素。

下面给出了一些示例，以更好地理解实现：

范例1：

// C# code to add key and value
// into OrderedDictionary
using System;
using System.Collections;
using System.Collections.Specialized;
  
class GFG {
  
    // Driver method
    public static void Main()
    {
  
        // Creating a orderedDictionary named myDict
        OrderedDictionary myDict = new OrderedDictionary();
  
        // Adding key and value in myDict
        myDict.Add("key1", "value1");
        myDict.Add("key2", "value2");
        myDict.Add("key3", "value3");
        myDict.Add("key4", "value4");
        myDict.Add("key5", "value5");
  
        // Displaying the number of key/value
        // pairs in myDict
        Console.WriteLine(myDict.Count);
  
        // Displaying the key/value pairs in myDict
        foreach(DictionaryEntry de in myDict)
            Console.WriteLine(de.Key + " --> " + de.Value);
    }
}

输出：

5
key1 --> value1
key2 --> value2
key3 --> value3
key4 --> value4
key5 --> value5

范例2：

// C# code to add key and value
// into OrderedDictionary
using System;
using System.Collections;
using System.Collections.Specialized;
  
class GFG {
  
    // Driver method
    public static void Main()
    {
  
        // Creating a orderedDictionary named myDict
        OrderedDictionary myDict = new OrderedDictionary();
  
        // Adding key and value in myDict
        myDict.Add("key1", "value1");
        myDict.Add("key2", "value2");
  
        // This should raise "ArgumentException"
        // as an element with the same key already
        // exists in the OrderedDictionary collection.
        myDict.Add("key2", "value3");
        myDict.Add("key4", "value4");
        myDict.Add("key5", "value5");
  
        // Displaying the number of key/value
        // pairs in myDict
        Console.WriteLine(myDict.Count);
  
        // Displaying the key/value pairs in myDict
        foreach(DictionaryEntry de in myDict)
            Console.WriteLine(de.Key + " --> " + de.Value);
    }
}

运行时错误：

Unhandled Exception:
System.ArgumentException: Item has already been added. Key in dictionary: ‘key2’ Key being added: ‘key2’

注意：键不能为null，但值可以为null。

参考：

• https://docs.microsoft.com/zh-cn/dotnet/api/system.collections.specialized.ordereddictionary.add?view=netframework-4.7.2