C# | Get or set the element at specified index in Collection<T>

Collection<T>.Item[Int32] property is used to get or set the element at the specified index.

Syntax:

public T this[int index] { get; set; }

Here, index is the zero-based index of the element to get or set.

Return Value: The element at the specified index.

Exception: This method will give ArgumentOutOfRangeException if the index is less than zero or index is equal to or greater than Count.

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

Example 1:

// C# code to get or set the
// element at the specified index
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

class GFG {

    // Driver code
    public static void Main()
    {
        // Creating a collection of strings
        Collection<string> myColl = new Collection<string>();

        // Adding elements in Collection myColl
        myColl.Add("A");
        myColl.Add("B");
        myColl.Add("C");
        myColl.Add("D");
        myColl.Add("E");

        // Displaying the elements in myColl
        foreach(string str in myColl)
        {
            Console.WriteLine(str);
        }

        // Get the element at index 2
        Console.WriteLine("Element at index 2 is : " + myColl[2]);

        // Get the element at index 3
        Console.WriteLine("Element at index 3 is : " + myColl[3]);

        // Set the element at index 3
        myColl[3] = "GFG";

        // Displaying the elements in myColl
        foreach(string str in myColl)
        {
            Console.WriteLine(str);
        }
    }
}

Output:

A
B
C
D
E
Element at index 2 is : C
Element at index 3 is : D
A
B
C
GFG
E

Example 2:

// C# code to get or set the
// element at the specified index
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

class GFG {

    // Driver code
    public static void Main()
    {
        // Creating a collection of ints
        Collection<int> myColl = new Collection<int>();

        // Adding elements in Collection myColl
        myColl.Add(2);
        myColl.Add(3);
        myColl.Add(4);
        myColl.Add(5);

        // Displaying the elements in myColl
        foreach(int i in myColl)
        {
            Console.WriteLine(i);
        }

        // Get the element at index -1
        // This should raise "ArgumentOutOfRangeException"
        // as the index is less than 0
        Console.WriteLine("Element at index -1 is : " + myColl[-1]);

        // Set the element at index 2
        myColl[2] = 10;

        // Displaying the elements in myColl
        foreach(int i in myColl)
        {
            Console.WriteLine(i);
        }
    }
}

Runtime Error:

Unhandled Exception:
System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

Note:

• Collection<T> accepts null as a valid value for reference types and allows duplicate elements.
• This property provides the ability to access a specific element in the collection by using the syntax : myCollection[index].
• Retrieving the value of this property is an O(1) operation.
• Setting the property is also an O(1) operation.

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.objectmodel.collection-1.item?view=netframework-4.7.2