Part 66 - C# Tutorial - Overloading indexers in c#

Suggested Videos 
Part 63 - Partial methods
Part 64 - How and where are indexers used in .net
Part 65 - Indexers in c#



In this video we will discuss about Overloading indexers in c#. Please watch Part 64 and Part 65 before proceeding. We will be modifying the example, that we discussed in Part 65.



In Part 65, we discussed about creating an indexer based on integer parameter. 
public string this[int employeeId]
{
    get
    {
        return listEmployees.
            FirstOrDefault(x => x.EmployeeId == employeeId).Name;
    }
    set
    {
        listEmployees.
            FirstOrDefault(x => x.EmployeeId == employeeId).Name = value;
    }
}

Now let us create another indexer based on a string parameter.
public string this[string gender]
{
    get
    {
        // Returns the total count of employees whose gender matches
        // with the gender that is passed in.
        return listEmployees.Count(x => x.Gender == gender).ToString();
    }
    set
    {
        // Changes the gender of all employees whose gender matches
        // with the gender that is passed in.
        foreach (Employee employee in listEmployees)
        {
            if (employee.Gender == gender)
            {
                employee.Gender = value;
            }
        }
    }
}

Please note that, indexers can be overloaded based on the number and type of parameters.

Here is the complete code of Company class. 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

namespace Demo
{
    public class Employee
    {
        public int EmployeeId { get; set; }
        public string Name { get; set; }
        public string Gender { get; set; }
    }

    public class Company
    {
        private List<Employee> listEmployees;

        public Company()
        {
            listEmployees = new List<Employee>();

            listEmployees.Add(new Employee 
            { EmployeeId = 1, Name = "Mike", Gender = "Male" });
            listEmployees.Add(new Employee 
            { EmployeeId = 2, Name = "Pam", Gender = "Female" });
            listEmployees.Add(new Employee 
            { EmployeeId = 3, Name = "John", Gender = "Male" });
            listEmployees.Add(new Employee 
            { EmployeeId = 4, Name = "Maxine", Gender = "Female" });
            listEmployees.Add(new Employee 
            { EmployeeId = 5, Name = "Emiliy", Gender = "Female" });
            listEmployees.Add(new Employee 
            { EmployeeId = 6, Name = "Scott", Gender = "Male" });
            listEmployees.Add(new Employee 
            { EmployeeId = 7, Name = "Todd", Gender = "Male" });
            listEmployees.Add(new Employee 
            { EmployeeId = 8, Name = "Ben", Gender = "Male" });
        }

        public string this[int employeeId]
        {
            get
            {
                return listEmployees.
                    FirstOrDefault(x => x.EmployeeId == employeeId).Name;
            }
            set
            {
                listEmployees.
                    FirstOrDefault(x => x.EmployeeId == employeeId).Name = value;
            }
        }

        public string this[string gender]
        {
            get
            {
                return listEmployees.Count(x => x.Gender == gender).ToString();
            }
            set
            {
                foreach (Employee employee in listEmployees)
                {
                    if (employee.Gender == gender)
                    {
                        employee.Gender = value;
                    }
                }
            }
        }
    }
}

Notice that the Company class has 2 indexers. The first indexer has an integer (employeeId) parameter and the second indexer has got a string (gender) parameter.

To test the string indexer, that we have just created, copy and paste the following code in Page_Load() event of WebForm1.aspx.cs

Company company = new Company();

Response.Write("Before changing the Gender of all male employees to Female");
Response.Write("<br/>");

// Get accessor of string indexer is invoked to return the total
// count of male employees
Response.Write("Total Employees with Gender = Male:" + company["Male"]);
Response.Write("<br/>");
Response.Write("Total Employees with Gender = Female:" + company["Female"]);
Response.Write("<br/>");
Response.Write("<br/>");

// Set accessor of string indexer is invoked to change the gender
// all "Male" employees to "Female"
company["Male"] = "Female";

Response.Write("After changing the Gender of all male employees to Female");
Response.Write("<br/>");
Response.Write("Total Employees with Gender = Male:" + company["Male"]);
Response.Write("<br/>");
Response.Write("Total Employees with Gender = Female:" + company["Female"]);