两点的C#集合不返回任何结果

Question

类：

public class Point : IEqualityComparer<Point>
{               
    public char HorizontalPosition { get; set; }
    public int VerticalPosition { get; set; }

    public Point(char horizontalPosition, int verticalPosition)
    {
        HorizontalPosition = char.ToUpper(horizontalPosition);
        VerticalPosition = verticalPosition;           
    }   

    public bool Equals(Point x, Point y)
    {
        return (x.VerticalPosition == y.VerticalPosition && x.HorizontalPosition == y.HorizontalPosition);
    }

    public int GetHashCode(Point obj)
    {
        return (obj.HorizontalPosition.GetHashCode() + obj.VerticalPosition.GetHashCode());
    }
}

我试图在两个集合中找到公共点(交集)，但是结果是空集合--其中应该包含两个元素。为什么？我已经实现了IEqualityComparer。我做错什么了吗？

示例集合：

  List<Point> first = new List<Point> { new Point('a', 1), new Point('b', 2) };
  List<Point> second = new List<Point> { new Point('a', 1), new Point('b', 2) };
  List<Point> intersection = first.Intersect(second).ToList();

交集是空列表，但其中应该包含两个元素。

Answer 1

List<Point> first = new List<Point> { new Point('a', 1), new Point('b', 2) };
            List<Point> second = new List<Point> { new Point('a', 1), new Point('b', 2) };
            List<Point> intersection = first.Intersect(second, new PointComparer()).ToList();


public class Point 
{
    public char HorizontalPosition { get; set; }
    public int VerticalPosition { get; set; }

    public Point(char horizontalPosition, int verticalPosition)
    {
        HorizontalPosition = char.ToUpper(horizontalPosition);
        VerticalPosition = verticalPosition;
    }
}

public class PointComparer : IEqualityComparer<Point>
{
    public bool Equals(Point x, Point y)
    {
        return (x.VerticalPosition == y.VerticalPosition && x.HorizontalPosition == y.HorizontalPosition);
    }

    public int GetHashCode(Point obj)
    {
        return (obj.HorizontalPosition.GetHashCode() + obj.VerticalPosition.GetHashCode());
    }
}

试试上面的例子

Answer 2

IEqualityComparer是您可以提供给Intersect方法比较项的接口。默认情况下，它不用于比较任何事物。因此，您的代码只是使用Object中内置的Object，它将返回false，除非对象是同一个对象。

您必须重写类中的默认Equal和GetHashCode方法，或者告诉交集使用比较器的实现。但是您不应该在数据存储类中实现比较器。

Answer 3

您应该从object重写Equals和GetHashCode：

public class Point
{
    public char HorizontalPosition { get; set; }
    public int VerticalPosition { get; set; }

    public Point(char horizontalPosition, int verticalPosition)
    {
        HorizontalPosition = char.ToUpper(horizontalPosition);
        VerticalPosition = verticalPosition;
    }

    public override int GetHashCode()
    {
        unchecked
        { 
            return (HorizontalPosition * 397) ^ VerticalPosition;
        }
    }

    protected bool Equals(Point other)
    {
        return Equals(HorizontalPosition, other.HorizontalPosition) && Equals(VerticalPosition, other.VerticalPosition);
    }

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(null, obj)) return false;
        if (ReferenceEquals(this, obj)) return true;
        if (obj.GetType() != this.GetType()) return false;
        return Equals((Point)obj);
    }
}

还可以实现自定义IEqualityComparer并将其传递给intersect。

public class PointComparer : IEqualityComparer<Point>
{
    public bool Equals(Point a, Point b)
    {
        return a.HorizontalPosition == b.HorizontalPosition && a.VerticalPosition == b.VerticalPosition;
    }

    public int GetHashCode(Point p)
    {
        unchecked
        { 
            return (p.HorizontalPosition * 397) ^ p.VerticalPosition;
        }
    }
}

// ...

List<Point> intersection = first.Intersect(second, new PointComparer()).ToList();

正如@decPL的注释中所提到的，您还应该重新考虑您的哈希代码实现。