Farkı Arabirimleri'nde (C# ve Visual Basic) genel koleksiyonları için kullanma
Değişkenle birlikte arabirim yöntemlerini türetilmiş türler arabiriminde belirtilen haklardan daha geri dönmek izin verir.Karşıtı arabirim yöntemlerini arabiriminde SQL'den daha az türetilmiş türlerinin parametrelerini kabul etmek izin verir.
.net Framework 4, birçok varolan arabirimler değişkenle birlikte olur ve karşıtı.Bunlar IEnumerable<T> ve IComparable<T>.Temel türlerinden türetilmiþ tür koleksiyonları için genel toplulukla çalışması yöntemleri yeniden kullanmanıza olanak sağlar.
Varyant Arabirimleri'nde listesi.net Framework Bkz: Varyans Generic arabirimlerden (C# ve Visual Basic).
Genel Koleksiyonlar dönüştürme
Kovaryans desteği avantajları aşağıdaki örnekte gösterilmektedir IEnumerable<T> arabirimi.PrintFullName Yöntemi kabul topluluğu IEnumerable<Person> türü (IEnumerable(Of Person) Visual Basic) parametre olarak.Ancak, topluluğu için kullanabilir IEnumerable<Employee> türü (IEnumerable(Of Person) Visual Basic) çünkü Employee devralan Person.
' Simple hierarchy of classes.
Public Class Person
Public Property FirstName As String
Public Property LastName As String
End Class
Public Class Employee
Inherits Person
End Class
' The method has a parameter of the IEnumerable(Of Person) type.
Public Sub PrintFullName(ByVal persons As IEnumerable(Of Person))
For Each person As Person In persons
Console.WriteLine(
"Name: " & person.FirstName & " " & person.LastName)
Next
End Sub
Sub Main()
Dim employees As IEnumerable(Of Employee) = New List(Of Employee)
' You can pass IEnumerable(Of Employee),
' although the method expects IEnumerable(Of Person).
PrintFullName(employees)
End Sub
// Simple hierarchy of classes.
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
}
public class Employee : Person { }
class Program
{
// The method has a parameter of the IEnumerable<Person> type.
public static void PrintFullName(IEnumerable<Person> persons)
{
foreach (Person person in persons)
{
Console.WriteLine("Name: {0} {1}",
person.FirstName, person.LastName);
}
}
public static void Test()
{
IEnumerable<Employee> employees = new List<Employee>();
// You can pass IEnumerable<Employee>,
// although the method expects IEnumerable<Person>.
PrintFullName(employees);
}
}
Genel Koleksiyonlar karşılaştırma
Contravariance destek avantajları aşağıdaki örnekte gösterilmektedir IComparer<T> arabirimi.PersonComparer Implements sınıfı IComparer<Person> arabirimi (IComparer(Of Person) Visual Basic).Ancak, bu sınıf nesnelerinin bir dizisi karşılaştırmak için yeniden Employee yazın, çünkü Employee devralan Person.
' Simple hierarhcy of classes.
Public Class Person
Public Property FirstName As String
Public Property LastName As String
End Class
Public Class Employee
Inherits Person
End Class
' The custom comparer for the Person type
' with standard implementations of Equals()
' and GetHashCode() methods.
Class PersonComparer
Implements IEqualityComparer(Of Person)
Public Function Equals1(
ByVal x As Person,
ByVal y As Person) As Boolean _
Implements IEqualityComparer(Of Person).Equals
If x Is y Then Return True
If x Is Nothing OrElse y Is Nothing Then Return False
Return (x.FirstName = y.FirstName) AndAlso
(x.LastName = y.LastName)
End Function
Public Function GetHashCode1(
ByVal person As Person) As Integer _
Implements IEqualityComparer(Of Person).GetHashCode
If person Is Nothing Then Return 0
Dim hashFirstName =
If(person.FirstName Is Nothing,
0, person.FirstName.GetHashCode())
Dim hashLastName = person.LastName.GetHashCode()
Return hashFirstName Xor hashLastName
End Function
End Class
Sub Main()
Dim employees = New List(Of Employee) From {
New Employee With {.FirstName = "Michael", .LastName = "Alexander"},
New Employee With {.FirstName = "Jeff", .LastName = "Price"}
}
' You can pass PersonComparer,
' which implements IEqualityComparer(Of Person),
' although the method expects IEqualityComparer(Of Employee)
Dim noduplicates As IEnumerable(Of Employee) = employees.Distinct(New PersonComparer())
For Each employee In noduplicates
Console.WriteLine(employee.FirstName & " " & employee.LastName)
Next
End Sub
// Simple hierarchy of classes.
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
}
public class Employee : Person { }
// The custom comparer for the Person type
// with standard implementations of Equals()
// and GetHashCode() methods.
class PersonComparer : IEqualityComparer<Person>
{
public bool Equals(Person x, Person y)
{
if (Object.ReferenceEquals(x, y)) return true;
if (Object.ReferenceEquals(x, null) ||
Object.ReferenceEquals(y, null))
return false;
return x.FirstName == y.FirstName && x.LastName == y.LastName;
}
public int GetHashCode(Person person)
{
if (Object.ReferenceEquals(person, null)) return 0;
int hashFirstName = person.FirstName == null
? 0 : person.FirstName.GetHashCode();
int hashLastName = person.LastName.GetHashCode();
return hashFirstName ^ hashLastName;
}
}
class Program
{
public static void Test()
{
List<Employee> employees = new List<Employee> {
new Employee() {FirstName = "Michael", LastName = "Alexander"},
new Employee() {FirstName = "Jeff", LastName = "Price"}
};
// You can pass PersonComparer,
// which implements IEqualityComparer<Person>,
// although the method expects IEqualityComparer<Employee>.
IEnumerable<Employee> noduplicates =
employees.Distinct<Employee>(new PersonComparer());
foreach (var employee in noduplicates)
Console.WriteLine(employee.FirstName + " " + employee.LastName);
}
}