Queryable.OfType<TResult>(IQueryable) Method

Definition

Filtra gli elementi di un oggetto IQueryable in base a 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)

Type Parameters

TResult

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

Parameters

source
IQueryable

Un oggetto IQueryable i cui elementi devono essere filtrati.An IQueryable whose elements to filter.

Returns

IQueryable<TResult>

Raccolta che contiene elementi da source che sono di tipo TResult.A collection that contains the elements from source that have type TResult.

Exceptions

source è null.source is null.

Examples

Nell'esempio di codice riportato di seguito 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

Remarks

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

Il comportamento della query che si verifica in seguito all'esecuzione di un albero delle espressioni che rappresenta la chiamata di OfType dipende dall'implementazione del tipo del parametro source.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 filtra 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.

Applies to