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

Definizione

Restituisce l'input tipizzato come oggetto 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)

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

Parametri

source
IEnumerable<TSource>

Sequenza da digitare come oggetto IEnumerable<T>.The sequence to type as IEnumerable<T>.

Restituisce

IEnumerable<TSource>

Sequenza di input digitata come oggetto IEnumerable<T>.The input sequence typed as IEnumerable<T>.

Esempio

Nell'esempio di codice riportato di seguito viene illustrato come utilizzare AsEnumerable<TSource>(IEnumerable<TSource>) per nascondere il metodo Where personalizzato di un tipo quando si desidera l'implementazione dell'operatore di query standard.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.

Commenti

Il metodo AsEnumerable<TSource>(IEnumerable<TSource>) non ha alcun effetto tranne che per modificare il tipo di source in fase di compilazione da un tipo che implementa IEnumerable<T> per IEnumerable<T> stesso.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.

è possibile utilizzare AsEnumerable<TSource>(IEnumerable<TSource>) per scegliere tra implementazioni di query quando una sequenza implementa IEnumerable<T> ma dispone anche di un set diverso di metodi di query pubblici disponibili.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. Ad esempio, data una classe generica Table che implementa IEnumerable<T> e dispone di metodi propri, ad esempio Where, Selecte SelectMany, una chiamata a Where richiama il metodo Where pubblico di 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. Un tipo di Table che rappresenta una tabella di database può avere un metodo Where che accetta l'argomento del predicato come albero delle espressioni e converte l'albero in SQL per l'esecuzione remota.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. Se l'esecuzione remota non è desiderata, ad esempio perché il predicato richiama un metodo locale, è possibile usare il metodo AsEnumerable per nascondere i metodi personalizzati e rendere disponibili gli operatori di query standard.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.

Si applica a