C# Generic Collections Part 5: Using Icomparer Interface

In the previous content we use Icomparable interface to sorting the list. There was a employee class which was created by me.If the class was created by some one and i had not the access of the code then how can i sort the list implementing the CompareTo() method. For get rid of this problem we use the Icomparer Interface.

The role of IComparer is to provide additional comparison mechanisms. For example, you may want to provide ordering of your class on several fields or properties, ascending and descending order on the same field, or both. 

Using IComparer is a two-step process. First, declare a class that implements IComparer, and then implement the Compare method.

Code:

1. using System;  
2. using System.Collections.Generic;  
3. using System.Linq;  
4. using System.Text;  
5. using System.Threading.Tasks;  
6.   
7. namespace genericUserDefined  
8. {  
9.     public class Employee : IComparable<Employee>  
10.     {  
11.         public int eid { get; set; }  
12.         public string first_name { get; set; }  
13.         public string last_name { get; set; }  
14.         public string department { get; set; }  
15.         public double salary { get; set; }  
16.   
17.         public int CompareTo(Employee other)  
18.         {  
19.             if (this.eid > other.eid)  
20.                 return 1;  
21.             else if (this.eid < other.eid)  
22.                 return -1;  
23.             else  
24.                 return 0;  
25.         }  
26.     }  
27.     public class compareEmployee : IComparer<Employee> //Using Icomparer Interface  
28.     {  
29.   
30.         public int Compare(Employee x, Employee y) // Implementing the compare method.  
31.         {  
32.             if (x.salary > y.salary)  
33.                 return 1;  
34.             else if (x.salary < y.salary)  
35.                 return -1;  
36.             else  
37.                 return 0;  
38.         }  
39.     }  
40. }  
41.   
42.   
43. //Main class  
44.   
45. using System;  
46. using System.Collections.Generic;  
47. using System.Linq;  
48. using System.Text;  
49. using System.Threading.Tasks;  
50.   
51. namespace genericUserDefined  
52. {  
53.     class Program  
54.     {  
55.         static void Main(string[] args)  
56.         {  
57.             List<Employee> elist = new List<Employee>();  
58.   
59.             Employee e1 = new Employee();  
60.             e1.eid = 101;  
61.             e1.first_name = "Sujan";  
62.             e1.last_name = "Hasan";  
63.             e1.department = "IT";  
64.             e1.salary = 55000.00;  
65.   
66.             elist.Add(e1);  
67.   
68.             Employee e2 = new Employee();  
69.             e2.eid = 102;  
70.             e2.first_name = "Shakil";  
71.             e2.last_name = "Sorker";  
72.             e2.department = "Networking";  
73.             e2.salary = 175000.00;  
74.   
75.             elist.Add(e2);  
76.   
77.             Employee e3 = new Employee();  
78.             e3.eid = 100;  
79.             e3.first_name = "Shimul";  
80.             e3.last_name = "Hossain";  
81.             e3.department = "Marketing";  
82.             e3.salary = 75000.50;  
83.             elist.Add(e3);  
84.   
85.               
86.   
87.             print(elist);  
88.             Console.WriteLine("\nAfter sorting the value with respect of employee id:\n");  
89.             elist.Sort();  
90.             print(elist);  
91.   
92.             Console.WriteLine("\nSorting with respect to salary:\n");  
93.             compareEmployee obj = new compareEmployee();  
94.             elist.Sort(obj);  
95.             print(elist);  
96.   
97.             Console.ReadKey();  
98.         }  
99.         public static void print(List<Employee> emp)  
100.         {  
101.             foreach (Employee obj in emp)  
102.             {  
103.                 Console.WriteLine(obj.eid+" "+obj.first_name+" "+obj.last_name+" "+obj.department+" "+obj.salary);  
104.             }  
105.         }  
106.     }  
107. }