Sorting an ArrayList by using IComparer Compare Function C#

Question

How do I sort a List of Points by using an customized compare method?

using System;
using System.Collections;
using System.Collections.Generic;

public class Point : IComparer<Point>
{
    public int x;
    public int y;

    public Point(int x_Point, int y_Point)
    {
        x = x_Point;
        y = y_Point;
    }
    public int Compare(Point a, Point b)
    {
        if (a.x == b.x && a.y == b.y)
            return 0;
        if (a.y < b.y)
            return -1;
        if (a.y == b.y && a.x < b.x)
            return -1;
        return 1;
    }
}

The code below throws an error at AL.sort().

"Failed to compare two elements in the array." "ArgumentException: At least one object must implement IComparable"

I have no clue why. Did I described my own comparing method at the Points class wrong?

public class ArrayListTest
{
    public static void Main(string[] args)
    {
        ArrayList AL = new ArrayList();
        Random R = new Random();
        for (int i = 0; i < 10; i++)
        {
            Point p = new Point(R.Next(50), R.Next(50));
            AL.Add(p);
        }
        PrintValues(AL);
        AL.Sort();
        PrintValues(AL);
    }
}

" an error" . I wonder if you could guess my next quesstion.... — Jeroen van Langen
– Jeroen van Langen, Commented Feb 12, 2020 at 20:19
Don't use ArrayList instead use List<Point>. ArrayList is a left over from the dark days before generics. Also you should be implementing IComparable instead of IComparer as the former is to indicate that the type can compared to other instances of the same type and the later just indicates that it can compare two instances of a given type. — juharr
– juharr, Commented Feb 12, 2020 at 20:22
Here's how you can setup a class to be comparable learn.microsoft.com/en-us/dotnet/api/… — juharr
– juharr, Commented Feb 12, 2020 at 20:26

Jeroen van Langen · Accepted Answer · 2020-02-12 20:34:38Z

You'd better use the IComparable<> interface.

"The object to be sorted will implement IComparable while the class that is going to sort the objects will implement IComparer."

Source: difference between IComparable and IComparer

public class Point : IComparable<Point>
{
    public int x;
    public int y;

    public Point(int x_Point, int y_Point)
    {
        x = x_Point;
        y = y_Point;
    }

    public int CompareTo(Point other)
    {
        if (this.x == other.x && this.y == other.y)
            return 0;
        if (this.y < other.y)
            return -1;
        if (this.y == other.y && this.x < other.x)
            return -1;
        return 1;
    }
}

public static void Main()
{
    var AL = new List<Point>(); // ditch the ArrayList for good... ;-)
    Random R = new Random();
    for (int i = 0; i < 10; i++)
    {
        Point p = new Point(R.Next(50), R.Next(50));
        AL.Add(p);
    }
    PrintValues(AL);
    AL.Sort();
    PrintValues(AL);

}

Collectives™ on Stack Overflow

Sorting an ArrayList by using IComparer Compare Function C#

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related