[英]Using equality comparer in lambda expression
我有一個Venue類和一個Coordinate類,如下所示:
class Venue
{
string Name;
Coordinate coordinate;
}
class Coordinate
{
double latitute;
double longitude;
}
現在,我希望能夠根據如下所示的坐標來選擇場地:
List<Venue> venues = GetAllVenues();
var myVenue = venues.FirstOrDefault(venue=>venue.coordinate == myCoordinate);
我有IEqualityComparer實現,但是lambda表達式沒有將IEqualityComparer作為參數的重載。
如何在lambda表達式中使用我的相等比較器?
編輯:
我的平等比較器如下所示:
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();
}
}
當我像這樣執行Union()操作時,即使兩個列表中的坐標相同,它也無法正常工作。
List<Coordinates> coordinates;
CoordinatesEqualityComparer comparer;
coordinates.Union(someOtherListOfCoordinates, comparer);
但是,當我與自己進行聯合時,它會起作用。 我究竟做錯了什么? 它與GetHashCode()實現有關嗎?
編輯2:修復GetHashCode()方法似乎可以解決問題。
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 ;
}
你有沒有嘗試過:
var ec = new YourEqualityComparer();
var myVenue = venues.FirstOrDefault(venue =>
ec.Equals(venue.coordinate, myCoordinate));
當然,另一種方法是為您的Coordinate
類定義==
運算符,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);
}
}
我將實現IEquatable<Coordinate>
,覆蓋Equals(object),覆蓋GetHashCode()和==!=運算符,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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