Sorting an Array of Custom Objects in C#
page 3 of 4
by Sandesh Meda
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Method 2: Using the IComparer Interface

Sometimes, it might be necessary to have more flexibility in your sorting, for example, to provide which property you want to sort the Car array by. In situations like this, we would need to use the IComparer interface and use the overloaded Sort method that takes the comparer instance as an argument.

Step 1: Create a CarComparer class that implements the IComparer interface

Listing 6

class CarComparer: IComparer
  public enum ComparisonType
    Make = 1, Year, Location
  public ComparisonType ComparisonMethod
  public int Compare(object x, object y)
    Car c1;
    Car c2;
    if (x is Car)
      c1 = x as Car;
      throw new ArgumentException("Object is not of type Car.");
    if (y is Car)
      c2 = y as Car;
      throw new ArgumentException("Object is not of type Car.");
    return c1.CompareTo(c2, ComparisonMethod);

The main purpose of the CarComparer is to keep track of by what property we are sorting. It has a ComparisonType enum that has the property elements and an overloaded Compare method.

Step 2

Add an overloaded CompareTo to the Car class as shown in Listing 7.

Listing 7

public int CompareTo(Car c2, CarComparer.ComparisonType comparisonType)
  switch (comparisonType)
    case CarComparer.ComparisonType.Make:
      return Make.CompareTo(c2.Make);
    case CarComparer.ComparisonType.Year:
      return Year.CompareTo(c2.Year);
    case CarComparer.ComparisonType.Location:
      return Location.CompareTo(c2.Location);
      return Make.CompareTo(c2.Make);

That is it, we are done. We now have added the ability to sort by Make, Year or Location. Let us test it out.

Step 3

Listing 8

Car objCar = new Car();
ArrayList carArray = new ArrayList();
objCar.Make = "BMW";
objCar.Year = 2008;
objCar.Location = "Florida";
objCar = null;
objCar = new Car();
objCar.Make = "Honda";
objCar.Year = 1996;
objCar.Location = "Illinois";
objCar = null;
objCar = new Car();
objCar.Make = "Corvette";
objCar.Year = 2006;
objCar.Location = "ZZ";
objCar = null;
CarComparer carComparer = new CarComparer();
carComparer.ComparisonMethod = CarComparer.ComparisonType.Location;

We use the overloaded Sort method that takes an instance of the CarComparer class. To sort by other properties, change the ComparisonMethod as shown below.

carComparer.ComparisonMethod = CarComparer.ComparisonType.Year

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User Comments

Title: Great   
Name: peter
Date: 2011-09-02 5:41:56 AM
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Title: Thanx   
Name: Stef
Date: 2010-02-03 4:10:36 PM
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Title: Mast hai   
Name: Niraj kumar
Date: 2009-06-05 8:58:00 AM
Best explanation
Title: Well Done   
Name: jj
Date: 2009-06-03 2:28:54 AM
This is good work
Title: Excelent   
Name: Awais Ranjha
Date: 2009-05-11 4:52:25 PM
This is a great help. i am really thankful to the author. Really excellent article. Thanks a lot!
Title: Coustom object   
Name: shatendra singh
Date: 2009-05-02 6:34:28 AM
this is very well artical.
Title: Great   
Name: Anton
Date: 2009-01-14 2:13:57 PM
Thnx, very helpful
Title: great explanation   
Name: Aga
Date: 2008-11-28 11:50:20 PM
Thanks so much for giving great explanation of the subject!
Title: Useful one   
Name: Chennai Tours Travels
Date: 2008-10-20 3:56:09 AM
Nice explanation Sandesh Meda
Good effort ..
Title: Nice one   
Name: Ravi Sadalagi
Date: 2008-08-12 6:05:44 AM
good one thank you..
Title: Excellent   
Name: Nancy
Date: 2008-08-11 10:23:58 AM
Makes a great attempt to explain sorting an array of custom objects in a very easy understandable way. Really excellent article. Thanks a lot!
Title: Mr   
Name: Amook Vandan
Date: 2008-08-11 4:46:47 AM
good article
Title: good   
Name: Neetu Tiwari
Date: 2008-08-09 6:55:21 AM
Its good.....thanks
Title: Mr   
Name: Priyan R
Date: 2008-07-29 2:18:41 AM
Hi thanks good article

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