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

Definice

Vrátí vstup zadaný jako IEnumerable<T> .Returns the input typed as IEnumerable<T>.

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

TSource

Typ prvků source .The type of the elements of source.

Parametry

source
IEnumerable<TSource>

Sekvence, která se má napsat IEnumerable<T> .The sequence to type as IEnumerable<T>.

Návraty

IEnumerable<TSource>

Vstupní sekvence zadaná jako IEnumerable<T> .The input sequence typed as IEnumerable<T>.

Příklady

Následující příklad kódu ukazuje, jak použít AsEnumerable<TSource>(IEnumerable<TSource>) pro skrytí vlastní metody typu, Where když je požadována standardní implementace operátoru dotazu.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.

Poznámky

AsEnumerable<TSource>(IEnumerable<TSource>)Metoda nemá žádný vliv na změnu typu při kompilaci source z typu, který implementuje IEnumerable<T> IEnumerable<T> sám sobě.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>) dá se použít k výběru mezi implementacemi dotazů, když sekvence implementuje, IEnumerable<T> ale také má jinou sadu veřejných metod dotazů, které jsou k dispozici.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. Například s ohledem na obecnou třídu Table , která implementuje IEnumerable<T> a má své vlastní metody, jako například Where , Select a SelectMany , volání Where by způsobilo vyvolání veřejné Where metody 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, který představuje databázovou tabulku, může mít Where metodu, která přebírá argument predikátu jako strom výrazu a převádí strom na SQL pro vzdálené spuštění.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. Pokud vzdálené spuštění není žádoucí, například protože predikát vyvolá místní metodu, AsEnumerable lze použít metodu pro skrytí vlastních metod a místo toho nastavit k dispozici standardní operátory dotazu.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.

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