Enumerable.AsEnumerable<TSource>(IEnumerable<TSource>) Metoda

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TSource> ^ AsEnumerable(System::Collections::Generic::IEnumerable<TSource> ^ source);

public static System.Collections.Generic.IEnumerable<TSource> AsEnumerable<TSource> (this System.Collections.Generic.IEnumerable<TSource> source);

static member AsEnumerable : seq<'Source> -> seq<'Source>

<Extension()>
Public Function AsEnumerable(Of TSource) (source As IEnumerable(Of TSource)) As IEnumerable(Of TSource)

Parametry typu

Parametry

Zwraca

IEnumerable<TSource>

Sekwencja wejściowa wpisana jako IEnumerable<T> .The input sequence typed as IEnumerable<T>.

Przykłady

Poniższy przykład kodu demonstruje, jak użyć AsEnumerable<TSource>(IEnumerable<TSource>) do ukrycia niestandardowej Where metody typu, gdy wymagana jest implementacja standardowego operatora zapytań.The following code example demonstrates how to use AsEnumerable<TSource>(IEnumerable<TSource>) to hide a type's custom Where method when the standard query operator implementation is desired.

// Custom class.
class Clump<T> : List<T>
{
    // Custom implementation of Where().
    public IEnumerable<T> Where(Func<T, bool> predicate)
    {
        Console.WriteLine("In Clump's implementation of Where().");
        return Enumerable.Where(this, predicate);
    }
}

static void AsEnumerableEx1()
{
    // Create a new Clump<T> object.
    Clump<string> fruitClump =
        new Clump<string> { "apple", "passionfruit", "banana",
            "mango", "orange", "blueberry", "grape", "strawberry" };

    // First call to Where():
    // Call Clump's Where() method with a predicate.
    IEnumerable<string> query1 =
        fruitClump.Where(fruit => fruit.Contains("o"));

    Console.WriteLine("query1 has been created.\n");

    // Second call to Where():
    // First call AsEnumerable() to hide Clump's Where() method and thereby
    // force System.Linq.Enumerable's Where() method to be called.
    IEnumerable<string> query2 =
        fruitClump.AsEnumerable().Where(fruit => fruit.Contains("o"));

    // Display the output.
    Console.WriteLine("query2 has been created.");
}

// This code produces the following output:
//
// In Clump's implementation of Where().
// query1 has been created.
//
// query2 has been created.

Dim output As New System.Text.StringBuilder

' A custom class.
Class Clump(Of T)
    Inherits List(Of T)

    ' Constructor.
    Public Sub New(ByVal collection As IEnumerable(Of T))
        MyBase.New(collection)
    End Sub

    ' Custom implementation of Where().
    Function Where(ByVal predicate As Func(Of T, Boolean)) As IEnumerable(Of T)
        output.AppendLine("In Clump's implementation of Where().")
        Return Enumerable.Where(Me, predicate)
    End Function
End Class

Sub AsEnumerableEx1()
    ' Create a new Clump(Of T) object.
    Dim fruitClump As New Clump(Of String)(New String() _
                                       {"apple", "passionfruit", "banana",
                                        "mango", "orange", "blueberry",
                                        "grape", "strawberry"})

    ' First call to Where():
    ' Call Clump's Where() method with a predicate.
    Dim query1 As IEnumerable(Of String) =
    fruitClump.Where(Function(fruit) fruit.Contains("o"))
    output.AppendLine("query1 has been created." & vbCrLf)

    ' Second call to Where():
    ' First call AsEnumerable() to hide Clump's Where() method and thereby
    ' force System.Linq.Enumerable's Where() method to be called.
    Dim query2 As IEnumerable(Of String) =
    fruitClump.AsEnumerable().Where(Function(fruit) fruit.Contains("o"))
    output.AppendLine("query2 has been created.")

    ' Display the output.
    Console.WriteLine(output.ToString())
End Sub

' This code produces the following output:
'
' In Clump's implementation of Where().
' query1 has been created.
'
' query2 has been created.

Uwagi

AsEnumerable<TSource>(IEnumerable<TSource>)Metoda nie ma żadnego efektu niż zmiana typu czasu kompilacji z source typu, który implementuje IEnumerable<T> IEnumerable<T> sam.The AsEnumerable<TSource>(IEnumerable<TSource>) method has no effect other than to change the compile-time type of source from a type that implements IEnumerable<T> to IEnumerable<T> itself.

AsEnumerable<TSource>(IEnumerable<TSource>) może służyć do wybierania między implementacjami zapytań, gdy sekwencja implementuje, IEnumerable<T> ale również ma inny zestaw metod zapytania publicznego.AsEnumerable<TSource>(IEnumerable<TSource>) can be used to choose between query implementations when a sequence implements IEnumerable<T> but also has a different set of public query methods available. Na przykład, w przypadku klasy generycznej Table , która implementuje IEnumerable<T> i ma własne metody, takie jak Where , Select , i SelectMany , wywołanie Where wywoła metodę publiczną Where Table .For example, given a generic class Table that implements IEnumerable<T> and has its own methods such as Where, Select, and SelectMany, a call to Where would invoke the public Where method of Table. TableTyp reprezentujący tabelę bazy danych może mieć Where metodę, która przyjmuje argument predykat jako drzewo wyrażenia i konwertuje drzewo na SQL na potrzeby wykonywania zdalnego.A Table type that represents a database table could have a Where method that takes the predicate argument as an expression tree and converts the tree to SQL for remote execution. Jeśli zdalne wykonywanie nie jest wymagane, na przykład dlatego, że predykat wywołuje metodę lokalną, AsEnumerable można użyć metody do ukrycia metod niestandardowych i zamiast tego udostępnić standardowe operatory zapytań.If remote execution is not desired, for example because the predicate invokes a local method, the AsEnumerable method can be used to hide the custom methods and instead make the standard query operators available.

Dotyczy