Queryable.OfType<TResult>(IQueryable) 方法

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)

类型参数

参数

返回

包含具有类型的TResult元素source的集合。

属性

RequiresDynamicCodeAttribute

例外

示例

下面的代码示例演示如何从OfType类型MemberInfo元素列表中筛选出类型不是类型的PropertyInfo元素。

// 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

注解

该方法OfType生成一个表示调用OfType自身为已构造泛型方法的一MethodCallExpression个方法。 然后，它将传递给MethodCallExpressionCreateQuery(Expression)由参数属性source表示Provider的方法IQueryProvider。

执行表示调用 OfType 的表达式树导致的查询行为取决于参数类型的 source 实现。 预期行为是，它会筛选出类型不TResult为的任何元素source。