C# | Getting the keys in a SortedList object

Last Updated : 11 Jul, 2025
SortedList.Keys Property is used to get the keys in a SortedList object. Syntax: 
public virtual System.Collections.ICollection Keys { get; }
Property Value: An ICollection object containing the keys in the SortedList object. Below programs illustrate the use of above-discussed property: Example 1: CSharp 
// C# code to get an ICollection containing
// the keys in the SortedList
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a SortedList
        SortedList mylist = new SortedList();

        // Adding elements in SortedList
        mylist.Add("4", "Even");
        mylist.Add("9", "Odd");
        mylist.Add("5", "Odd and Prime");
        mylist.Add("2", "Even and Prime");

        // Get a collection of the keys.
        ICollection c = mylist.Keys;

        // Displaying the contents
        foreach(string str in c)
            Console.WriteLine(str + ": " + mylist[str]);
    }
}
Output: 
2: Even and Prime
4: Even
5: Odd and Prime
9: Odd
Example 2: CSharp 
// C# code to get an ICollection containing
// the keys in the SortedList.
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a SortedList
        SortedList mylist = new SortedList();

        // Adding elements in SortedList
        mylist.Add("India", "Country");
        mylist.Add("Chandigarh", "City");
        mylist.Add("Mars", "Planet");
        mylist.Add("China", "Country");

        // Get a collection of the keys.
        ICollection c = mylist.Keys;

        // Displaying the contents
        foreach(string str in c)
            Console.WriteLine(str + ": " + mylist[str]);
    }
}
Output: 
Chandigarh: City
China: Country
India: Country
Mars: Planet
Note:
  • The ICollection object is a read-only view of the keys of the SortedList object. Modifications made to the underlying SortedList are immediately reflected in the ICollection.
  • The elements of the ICollection are sorted in the same order as the keys of the SortedList.
  • This property is similar to the GetKeyList method but returns an ICollection object instead of an IList object.
  • This method is an O(1) operation.
Reference:
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