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

下列程式碼範例將示範如何使用 OfType ,從類型的專案清單中,篩選出不屬於類型的元素 PropertyInfo MemberInfoThe 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

OfType方法 MethodCallExpression 會產生,代表呼叫 OfType 本身做為已建立的泛型方法。The OfType method generates a MethodCallExpression that represents calling OfType itself as a constructed generic method. 然後,它會將傳遞 MethodCallExpression 給以 CreateQuery(Expression) 參數的屬性所表示的方法 IQueryProvider Provider sourceIt then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

執行表示呼叫的運算式樹狀架構所產生的查詢行為, OfType 取決於參數類型的實作為 sourceThe 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 source 不屬於類型的任何元素 TResultThe expected behavior is that it filters out any elements in source that are not of type TResult.

適用於