C# | Add key and value into OrderedDictionary collection

Last Updated : 01 Feb, 2019

OrderedDictionary.Add(Object, Object) method is used to add an entry with the specified key and value into the OrderedDictionary collection with the lowest available index.

Syntax:

public void Add (object key, object value);

Parameters:

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

Exceptions :

NotSupportedException : If the OrderedDictionary collection is read-only.
ArgumentException : If an element with the same key already exists in the OrderedDictionary collection.

Below given are some examples to understand the implementation in a better way:

Example 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);
    }
}

Output:

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

Example 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);
    }
}

Runtime Error:

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

Note: A key cannot be null, but a value can be.

Reference:

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

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