C# | OrderedDictionary.Item[Object] Property

There are two methods in the overload list of this property as follows: 

1. Item[Int32] : Used to get or set the value at the specified index.
2. Item[Object] : Used to get or set the value with the specified key. 

OrderedDictionary.Item[Int32] Property

This property is used to get or set the value at the specified index.
Syntax:

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

Here, index is the zero-based index of the value to get or set.
Return Value: The value of the item at the specified index.
Exceptions:

• NotSupportedException : If the OrderedDictionary collection is read-only.
• 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:

CSHARP

// C# code to get or set the value
// at the specified index for
// 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");

        // To get or set the value at the
        // specified index for OrderedDictionary
        Console.WriteLine(myDict[1]);
    }
}

Output:

value2

Example 2:

CSHARP

// C# code to get or set the value
// at the specified index for
// 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");

        // To get or set the value at the
        // specified index for OrderedDictionary
        // This should raise "ArgumentOutOfRangeException"
        // as index is less than 0
        Console.WriteLine(myDict[-3]);
    }
}

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: This property allows you to access a specific element in the collection by using the syntax : myCollection[index]. 

OrderedDictionary.Item[Object] Property

This property is used to get or set the value with the specified key.
Syntax:

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

Here, key is the key of the 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 element using the specified key.
Exception : This property will give NotSupportedException if the property is being set and the OrderedDictionary collection is read-only.
Example:

CSHARP

// C# code to get or set the
// value with the specified key
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");

        // To get or set the value
        // with the specified key
        Console.WriteLine(myDict["key3"]);
    }
}

Output:

value3

Note: 

• This property allows you to access a specific element in the collection by using the syntax : myCollection[key].
• A key cannot be null, but a value can be.

Reference:

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