Sorting List by IComparable vs IComparer

List<T> class has a Sort() method which sorts the elements in the entire List<T> using the default comparer. (<T> => , ...)

List<string> strList = new List<string>();

strList.Add("Ss");

strList.Add("As");

strList.Add("Rs");

strList.Add("Ks");

strList.Sort();

foreach (string item in strList)

{

    Console.WriteLine(item);

}

IComparable - Sorting list of complex type like List<Employee> using IComparable and only by one way.

public class Employee

{

    public string Name { get; set; }

    public int Age { get; set; }

}

List<Employee> employee = new List<Employee>();

employee.Add(new Employee() { Name = "Ss", Age = 30 });

employee.Add(new Employee() { Name = "As", Age = 25 });

employee.Add(new Employee() { Name = "Rs", Age = 20 });

employee.Add(new Employee() { Name = "Ks", Age = 30 });

employee.Add(new Employee() { Name = "Av", Age = 50 });

employee.Sort();

foreach (Employee item in employee)

{

    Console.WriteLine("{0}, {1}", item.Name, item.Age);

}

So in order to do this we will have to implement Employee class by IComparable. and have to put sorting logic in implemented function CompareTo.

public class Employee : IComparable<Employee>

{

    public string Name { get; set; }

    public int Age { get; set; }

    public int CompareTo(Employee other)

    {

        if (this.Age == other.Age)

        {

            return this.Name.CompareTo(other.Name);

        }

        return this.Age.CompareTo(other.Age);

    }

}

IComparer - Used to sorting list of complex type using IComparer and by multiple ways like Name or by Age.

public class Employee

{

    public string Name { get; set; }

    public int Age { get; set; }

}

public class SortEmployeeByName : IComparer<Employee>

{

    public int Compare(Employee x, Employee y)

    {

        return string.Compare(x.Name, y.Name);

    }

}

public class SortEmployeeByAge : IComparer<Employee>

{

    public int Compare(Employee x, Employee y)

    {

        if (x.Age == x.Age)

        {

            return 0;

        }

        if (x.Age > y.Age)

        {

            return 1;

        }

        if (x.Age < y.Age)

        {

            return -1;

        }

        return 0;

    }

}

List<Employee> employee = new List<Employee>();

employee.Add(new Employee() { Name = "Ss", Age = 35 });

employee.Add(new Employee() { Name = "As", Age = 25 });

employee.Add(new Employee() { Name = "Rs", Age = 20 });

employee.Add(new Employee() { Name = "Ks", Age = 30 });

employee.Add(new Employee() { Name = "Av", Age = 50 });

//---------------

Console.WriteLine("By Name ....");

employee.Sort(new SortEmployeeByName());

foreach (Employee item in employee)

{

    Console.WriteLine("{0}, {1}", item.Name, item.Age);

}

//---------------

Console.WriteLine("By Age ....");

employee.Sort(new SortEmployeeByAge());

foreach (Employee item in employee)

{

    Console.WriteLine("{0}, {1}", item.Name, item.Age);

}