Queryable.OfType<TResult>(IQueryable) 方法

定義

根據指定的型別來篩選 IQueryable 的項目。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)

類型參數

TResult

用來做為序列項目之篩選依據的類型。The type to filter the elements of the sequence on.

參數

source
IQueryable

要篩選其項目的 IQueryableAn IQueryable whose elements to filter.

傳回

IQueryable<TResult>

集合,其中包含 source 中型別為 TResult 的項目。A collection that contains the elements from source that have type TResult.

例外狀況

sourcenullsource is null.

範例

下列程式碼範例示範如何使用OfType , 從類型MemberInfo的專案清單中篩選出不PropertyInfo屬於類型的元素。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

備註

方法會產生, 其代表以OfType結構化泛型方法的方式呼叫本身。 MethodCallExpression OfTypeThe OfType method generates a MethodCallExpression that represents calling OfType itself as a constructed generic method. 然後, 它會MethodCallExpression將傳遞CreateQuery(Expression)至由Provider source參數IQueryProvider的屬性所表示之的方法。It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

因執行代表呼叫OfType之運算式樹狀架構而產生的查詢行為, 取決於source參數類型的實作為。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. 預期的行為是, 它會篩選出不屬於source類型TResult的任何元素。The expected behavior is that it filters out any elements in source that are not of type TResult.

適用於