Using IComparer for sorting

Question

I am trying to use an IComparer to sort a list of Points. Here is the IComparer class:

public class CoordinatesBasedComparer : IComparer {     public int Compare(Object q, Object r)     {         Point a = (p)q;         Point b = (p)r;         if ((a.x == b.x) && (a.y == b.y))             return 0;         if ((a.x < b.x) || ((a.x == b.x) && (a.y < b.y)))             return -1;          return 1;     } } 

In the client code, I am trying to using this class for sorting a list of points p (of type List<Point>):

CoordinatesBasedComparer c = new CoordinatesBasedComparer(); Points.Sort(c); 

The code errors out. Apparently it is expecting IComparer<Point> as argument to sort method.
What do I need to do to fix this?

Answer 1

You need to implement the strongly type interface (MSDN).

public class CoordinatesBasedComparer : IComparer<Point> {     public int Compare(Point a, Point b)     {         if ((a.x == b.x) && (a.y == b.y))             return 0;         if ((a.x < b.x) || ((a.x == b.x) && (a.y < b.y)))             return -1;          return 1;     } } 

BTW, I think you use too many braces, I believe they should be used only when they contribute to the compiler. This is my version:

if (a.x == b.x && a.y == b.y)     return 0; if (a.x < b.x || (a.x == b.x && a.y < b.y))     return -1; 

Just like I dislike people using return (0).

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Note that if you target a .Net-3.5+ application you can use LINQ which is easier and even faster with sorting.

LINQ vesion can be something like:

var orderedList = Points.OrderBy(point => point.x)                         .ThenBy(point => point.y)                         .ToList(); 

Answer 2

public class CoordinatesBasedComparer : IComparer, IComparer<Point> {     public int Compare(Point a, Point b)     {         if ((a.x == b.x) && (a.y == b.y))             return 0;         if ((a.x < b.x) || ((a.x == b.x) && (a.y < b.y)))             return -1;          return 1;     }     int IComparer.Compare(Object q, Object r)     {         return Compare((Point)q, (Point)r);                 } }