C# Cookbook

3.5. Making a Type Sortable

Problem

You have a data type that will be stored as elements in an array or an ArrayList. You would like to use the Array.Sort and ArrayList.Sort methods to allow for a custom sorting of your data types in the array. In addition, you may need to use this structure in a SortedList collection.

Solution

Implement the IComparable interface. The following class, Square, implements this interface in a way so that the Array, ArrayList, and SortedList objects can sort and search an array or collection of these Square objects:

public class Square : IComparable
{
    public Square( ){}
    public Square(int height, int width)
    {
        this.height = height;
        this.width = width;
    }

    private int height;
    private int width;

    public int Height
    {
        get{ return (height); }
        set{ height = value; }
    }

    public int Width
    {
        get{ return (width); }
        set{ width = value; }
    }

    public int CompareTo(object obj)
    {
        if (this.GetType( ) != obj.GetType( ))
        {
            throw (new ArgumentException(
                   "Both objects being compared must be of type Square."));
        }
        else
        {
            Square square2 = (Square)obj;

            long area1 = this.Height * this.Width;
            long area2 = square2.Height * square2.Width;

            if (area1 == area2)
            {
                return (0);
            }
            else if (area1 > area2)
            {
                return (1);
            }
            else if (area1 < area2)
            {
                return (-1);
            }
            else
            {
                return (-1);
            }
        }
    }

    public override string ToString( )
    {
        return ("Height:" + height + "  Width:" + width);
    }
}

Discussion

By implementing the IComparable interface on your class (or structure), you can take advantage of the sorting ...