.NET Tip: Sort an ArrayList Using a Custom Comparer Class Houston TX

provided by: 
Originally published at Internet.com

The Sort() method of the ArrayList class allows you to provide your own comparer. When you provide a comparison object, your Compare() method will be used to compare objects in the ArrayList when sorting. This flexibility allows you to sort by any means that you choose. This example will sort an ArrayList that contains objects of different types. The Compare() method sorts them based on the name of the data type of the object. First, take a look at the DataTypeComparer class that implements the IComparer interface and defines a Compare() method that does a comparison based on the names of the data types of two objects. public class DataTypeComparer : IComparer { public DataTypeComparer() {} public int Compare(object obj1, object obj2) { return obj1.GetType().ToString(). CompareTo(obj2.GetType().ToString()); } }

To use the new DataTypeComparer, you need to create an ArrayList, fill it with data, and then pass an instance of DataTypeComparer to the Sort() method of the ArrayList. Here is some sample code that creates an ArrayList and populates it with five different data types. It prints the data types and values of the unsorted items, sorts them using a DataTypeComparer object, and then prints the sorted items. ArrayList Items = new ArrayList(); // Add several different data types to the Items ArrayList Items.Add(5); Items.Add("C# Tip"); Items.Add(new object()); Items.Add(new DateTime()); Items.Add(9876543210); // Print out the unsorted list of items Debug.Print("Unsorted:\r\nData Type [Value]"); foreach (object item in Items) Debug.Print(" " + item.GetType().ToString() + " [" + item.ToString() + "]"); // Sort the items DataTypeComparer MyDataTypeComparer = new DataTypeComparer(); Items.Sort(MyDataTypeComparer); // Print out the list of items sorted by data type Debug.Print("Sorted:\r\nData Type [Value]"); foreach (object item in Items) Debug.Print(" " + item.GetType().ToString() + " [" + item.ToString() + "]");

Here is the output from executing the code above: Unsorted: Data Type [Value] System.Int32 [5] System.String [C# Tip] System.Object [System.Object] System.DateTime [1/1/0001 12:00:00 AM] System.Int64 [9876543210] Sorted: Data Type [Value] System.DateTime [1/1/0001 12:00:00 AM] System.Int32 [5] System.Int64 [9876543210] System.Object [System.Object] System.String [C# Tip]

You can see from the final output that the items are sorted by the data type of the item in the ArrayList. Try your hand at creating a custom comparer class that sorts on something other the data type.

About the Author

Jay Miller is a Software Engineer with Electronic Tracking Systems, a company dedicated to robbery prevention, apprehension, and recovery based in Carrollton, Texas. Jay has been working with .NET since the release of the first beta and is co-author of Learn Microsoft Visual Basic.Net In a Weekend. Jay can be reached via email at jmiller@sm-ets.com.

Author: Jay Miller

Read article at Internet.com site

Entrance Software

Entrance Software is a Software Development and Consulting company and a Microsoft Gold Certified Partner.

713-357-4930
1001 McKinney
Houston, TX
http://www.entrancesoftware.com

For mid-sized businesses that own or need software, Entrance Software is a Trusted Advisor. Unlike other contract programming or staffing companies, Entrance exclusively provides Professional Software Consultants who are not only technical geniuses, but also understand the business value of Sales, Profit, Productivity, Loyalty and Morale.

Entrance Software is a Microsoft Gold Certified Partner and develops custom software applications for businesses in a variety of industries including Oil and Gas, Exploration and Production, Manufacturing, Education, Legal and Medical Services.