[英]Using equality comparer in lambda expression
I have a Venue class, and a Coordinate class like so: 我有一个Venue类和一个Coordinate类,如下所示:
class Venue
{
string Name;
Coordinate coordinate;
}
class Coordinate
{
double latitute;
double longitude;
}
Now, I want to be able to select a venue based on a coordinate as follows: 现在,我希望能够根据如下所示的坐标来选择场地:
List<Venue> venues = GetAllVenues();
var myVenue = venues.FirstOrDefault(venue=>venue.coordinate == myCoordinate);
I have an IEqualityComparer implementation, but the lambda expression does not have an overload which takes the IEqualityComparer as a parameter. 我有IEqualityComparer实现,但是lambda表达式没有将IEqualityComparer作为参数的重载。
How do I use my equality comparer in a lambda expression? 如何在lambda表达式中使用我的相等比较器?
EDIT: 编辑:
My equality comparer looks like this: 我的平等比较器如下所示:
class CoordinatesEqualityComparer:IEqualityComparer<Coordinate>
{
public bool Equals(Coordinate x, Coordinate y)
{
return x.RowIndex == y.RowIndex && x.ColumnIndex == y.ColumnIndex;
}
public int GetHashCode(Coordinate obj)
{
return obj.GetHashCode();
}
}
When I do a Union() operation, like so, it does not work correctly, even though coordinates in both lists are same. 当我像这样执行Union()操作时,即使两个列表中的坐标相同,它也无法正常工作。
List<Coordinates> coordinates;
CoordinatesEqualityComparer comparer;
coordinates.Union(someOtherListOfCoordinates, comparer);
However, when I do a union with itself, it works. 但是,当我与自己进行联合时,它会起作用。 What am I doing wrong? 我究竟做错了什么? Does it have something to do with the GetHashCode() implementation? 它与GetHashCode()实现有关吗?
Edit 2: Fixing the GetHashCode() method seems to do the trick. 编辑2:修复GetHashCode()方法似乎可以解决问题。
public int GetHashCode(Coordinates obj)
{
// Warning:Hack. Use two prime numbers to generate a hash based on two properties.
return obj.RowIndex.GetHashCode() * 7 + obj.ColumnIndex.GetHashCode() * 13 ;
}
Have you tried: 你有没有尝试过:
var ec = new YourEqualityComparer();
var myVenue = venues.FirstOrDefault(venue =>
ec.Equals(venue.coordinate, myCoordinate));
Of course, another approach would be to define the ==
operator for your Coordinate
class and then you wouldn't need an IEqualityComparer
: 当然,另一种方法是为您的Coordinate
类定义==
运算符,然后就不需要IEqualityComparer
:
class Coordinate
{
double latitude;
double longitude;
public override bool Equals(object obj)
{
return Object.ReferenceEquals(this, obj)) ||
this == (other as Coordinate);
}
public static bool operator ==(Coordinate l, Coordinate r)
{
return ((object)l == null && (object)r == null) ||
((object)l != null && (object)r != null) &&
// equality check including epsilons, edge cases, etc.
}
public static bool operator !=(Coordinate l, Coordinate r)
{
return !(l == r);
}
}
I would implement IEquatable<Coordinate>
, override Equals(object), override GetHashCode(), and == != operators like this: 我将实现IEquatable<Coordinate>
,覆盖Equals(object),覆盖GetHashCode()和==!=运算符,如下所示:
public class Coordinate : IEquatable<Coordinate>
{
public double Latitide { get; set; }
public double Longitude { get; set; }
public bool Equals(Coordinate other)
{
if (other == null)
{
return false;
}
else
{
return this.Latitide == other.Latitide && this.Longitude == other.Longitude;
}
}
public override bool Equals(object obj)
{
return this.Equals(obj as Coordinate);
}
public override int GetHashCode()
{
return this.Latitide.GetHashCode() ^ this.Longitude.GetHashCode();
}
public static bool operator ==(Coordinate value1, Coordinate value2)
{
if (!Object.ReferenceEquals(value1, null) && Object.ReferenceEquals(value2, null))
{
return false;
}
else if (Object.ReferenceEquals(value1, null) && !Object.ReferenceEquals(value2, null))
{
return false;
}
else if (Object.ReferenceEquals(value1, null) && Object.ReferenceEquals(value2, null))
{
return true;
}
else
{
return value1.Latitide == value2.Latitide && value1.Longitude == value2.Longitude;
}
}
public static bool operator !=(Coordinate value1, Coordinate value2)
{
return !(value1 == value2);
}
}
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