Queryable.OfType(IQueryable) Queryable.OfType(IQueryable) Queryable.OfType(IQueryable) Queryable.OfType(IQueryable) Method

Definizione

Filtra gli elementi di un IQueryable basato su un tipo specificato.Filters the elements of an IQueryable based on a specified type.

public:
generic <typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TResult> ^ OfType(System::Linq::IQueryable ^ source);
public static System.Linq.IQueryable<TResult> OfType<TResult> (this System.Linq.IQueryable source);
static member OfType : System.Linq.IQueryable -> System.Linq.IQueryable<'Result>
<Extension()>
Public Function OfType(Of TResult) (source As IQueryable) As IQueryable(Of TResult)

Parametri di tipo

TResult

Il tipo in base al quale filtrare gli elementi della sequenza.The type to filter the elements of the sequence on.

Parametri

source
IQueryable IQueryable IQueryable IQueryable

Un IQueryable cui filtrare gli elementi.An IQueryable whose elements to filter.

Restituisce

IQueryable<TResult>

Una raccolta che contiene gli elementi dalla source che dispongono di tipo TResult.A collection that contains the elements from source that have type TResult.

Eccezioni

Esempi

Esempio di codice seguente viene illustrato come utilizzare OfType per filtrare gli elementi che non sono di tipo PropertyInfo da un elenco di elementi di tipo MemberInfo.The following code example demonstrates how to use OfType to filter out elements that are not of type PropertyInfo from a list of elements of type MemberInfo.

// Create a list of MemberInfo objects.
List<System.Reflection.MemberInfo> members = typeof(String).GetMembers().ToList();

// Return only those items that can be cast to type PropertyInfo.
IQueryable<System.Reflection.PropertyInfo> propertiesOnly =
    members.AsQueryable().OfType<System.Reflection.PropertyInfo>();

Console.WriteLine("Members of type 'PropertyInfo' are:");
foreach (System.Reflection.PropertyInfo pi in propertiesOnly)
    Console.WriteLine(pi.Name);

/*
    This code produces the following output:
 
    Members of type 'PropertyInfo' are:
    Chars
    Length
*/

' Create a list of MemberInfo objects.
Dim members As List(Of System.Reflection.MemberInfo) = GetType(String).GetMembers().ToList()

' Return only those items that can be cast to type PropertyInfo.
Dim propertiesOnly As IQueryable(Of System.Reflection.PropertyInfo) = _
        members.AsQueryable().OfType(Of System.Reflection.PropertyInfo)()

Dim output As New System.Text.StringBuilder
output.AppendLine("Members of type 'PropertyInfo' are:")
For Each pi As System.Reflection.PropertyInfo In propertiesOnly
    output.AppendLine(pi.Name)
Next

' Display the output.
MsgBox(output.ToString())

' This code produces the following output:

' Members of type 'PropertyInfo' are:
' Chars
' Length

Commenti

Il OfType metodo genera un MethodCallExpression che rappresenta una chiamata OfType stesso come un metodo generico costruito.The OfType method generates a MethodCallExpression that represents calling OfType itself as a constructed generic method. Passa quindi il MethodCallExpression per il CreateQuery(Expression) metodo del IQueryProvider rappresentato dal Provider proprietà del source parametro.It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

Il comportamento delle query che si verifica in seguito all'esecuzione di un albero delle espressioni che rappresenta una chiamata OfType dipende dall'implementazione del tipo del source parametro.The query behavior that occurs as a result of executing an expression tree that represents calling OfType depends on the implementation of the type of the source parameter. Il comportamento previsto è che esclude tutti gli elementi in source che non sono di tipo TResult.The expected behavior is that it filters out any elements in source that are not of type TResult.

Si applica a