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Queryable.OfType<TResult>(IQueryable) Metode

Definisi

Ruang nama:
System.Linq
Rakitan:
System.Core.dll, System.Linq.Queryable.dll
Rakitan:
netstandard.dll, System.Linq.Queryable.dll
Rakitan:
System.Linq.Queryable.dll
Rakitan:
System.Core.dll
Rakitan:
netstandard.dll
Sumber:
Queryable.cs
Sumber:
Queryable.cs
Sumber:
Queryable.cs
Sumber:
Queryable.cs
Sumber:
Queryable.cs

Memfilter elemen IQueryable berdasarkan jenis tertentu.

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);
[System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")]
public static System.Linq.IQueryable<TResult> OfType<TResult>(this System.Linq.IQueryable source);
static member OfType : System.Linq.IQueryable -> System.Linq.IQueryable<'Result>
[<System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")>]
static member OfType : System.Linq.IQueryable -> System.Linq.IQueryable<'Result>
<Extension()>
Public Function OfType(Of TResult) (source As IQueryable) As IQueryable(Of TResult)

Jenis parameter

TResult

Jenis untuk memfilter elemen urutan.

Parameter

source
IQueryable

Elemen IQueryable yang akan difilter.

Mengembalikan

IQueryable<TResult>

Koleksi yang berisi elemen dari source yang memiliki jenis TResult.

Atribut
RequiresDynamicCodeAttribute

Pengecualian

ArgumentNullException

source adalah null.

Contoh

Contoh kode berikut menunjukkan cara menggunakan OfType untuk memfilter elemen yang bukan jenis PropertyInfo dari daftar elemen jenis 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

Keterangan

Metode ini OfType menghasilkan MethodCallExpression yang mewakili pemanggilan OfType dirinya sebagai metode generik yang dibangun. Kemudian meneruskan MethodCallExpression ke CreateQuery(Expression) metode yang diwakili IQueryProvider oleh Provider properti source parameter.

Perilaku kueri yang terjadi sebagai akibat dari menjalankan pohon ekspresi yang mewakili panggilan OfType tergantung pada implementasi jenis source parameter. Perilaku yang diharapkan adalah bahwa ia memfilter elemen apa pun dalam source yang bukan jenis TResult.

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