C# | Get or set the value associated with specified key in ListDictionary

ListDictionary.Item[Object] property is used to get or set the value associated with the specified key.

Syntax:

public object this[object key] { get; set; }

Here, key is the key whose value to get or set.

Return Value : The value associated with the specified key. If the specified key is not found, attempting to get it returns null, and attempting to set it creates a new entry using the specified key.

Exception: This property will give ArgumentNullException if the key is null.

Example:

// C# code to get or set the value
// associated with the specified key
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a ListDictionary named myDict
        ListDictionary myDict = new ListDictionary();

        // 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(DictionaryEntry de in myDict)
        {
            Console.WriteLine(de.Key + " " + de.Value);
        }

        // Displaying the value associated
        // with key "Russia"
        Console.WriteLine(myDict["Russia"]);

        // Setting the value associated with key "Russia"
        myDict["Russia"] = "Saint Petersburg";

        // Displaying the value associated
        // with key "Russia"
        Console.WriteLine(myDict["Russia"]);

        // Displaying the value associated
        // with key "India"
        Console.WriteLine(myDict["India"]);

        // Setting the value associated with key "India"
        myDict["India"] = "Mumbai";

        // Displaying the value associated
        // with key "India"
        Console.WriteLine(myDict["India"]);

        // Displaying the key/value pairs in myDict
        foreach(DictionaryEntry de in myDict)
        {
            Console.WriteLine(de.Key + " " + de.Value);
        }
    }
}

Output:

Australia Canberra
Belgium Brussels
Netherlands Amsterdam
China Beijing
Russia Moscow
India New Delhi
Moscow
Saint Petersburg
New Delhi
Mumbai
Australia Canberra
Belgium Brussels
Netherlands Amsterdam
China Beijing
Russia Saint Petersburg
India Mumbai

Note:

• This property provides the ability to access a specific element in the collection by using the syntax : myCollection[key].
• A key cannot be null, but a value can.
• This method is an O(n) operation, where n is Count.

Reference:

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