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

定義

篩選的項目IQueryable根據指定的型別。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 IQueryable IQueryable IQueryable

IQueryable篩選其項目。An IQueryable whose elements to filter.

傳回

IQueryable<TResult>

集合,其中包含的項目source具有類型TResultA collection that contains the elements from source that have type TResult.

例外狀況

範例

下列程式碼範例示範如何使用OfType若要篩選掉不屬於類型的項目PropertyInfo型別的項目清單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方法會產生MethodCallExpression,表示呼叫OfType本身做為建構的泛型方法。The OfType method generates a MethodCallExpression that represents calling OfType itself as a constructed generic method. 它接著會傳遞MethodCallExpressionCreateQuery(Expression)方法IQueryProviderProvider屬性source參數。It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

因執行運算式樹狀架構表示呼叫的查詢行為OfType之型別的實作而定source參數。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,它會篩選中的任何項目source不是型別的TResultThe expected behavior is that it filters out any elements in source that are not of type TResult.

適用於