IteratorStateMachineAttribute 类

定义

public ref class IteratorStateMachineAttribute sealed : System::Runtime::CompilerServices::StateMachineAttribute

[System.AttributeUsage(System.AttributeTargets.Method, AllowMultiple=false, Inherited=false)]
public sealed class IteratorStateMachineAttribute : System.Runtime.CompilerServices.StateMachineAttribute

[System.AttributeUsage(System.AttributeTargets.Method, AllowMultiple=false, Inherited=false)]
[System.Serializable]
public sealed class IteratorStateMachineAttribute : System.Runtime.CompilerServices.StateMachineAttribute

[<System.AttributeUsage(System.AttributeTargets.Method, AllowMultiple=false, Inherited=false)>]
type IteratorStateMachineAttribute = class
    inherit StateMachineAttribute

[<System.AttributeUsage(System.AttributeTargets.Method, AllowMultiple=false, Inherited=false)>]
[<System.Serializable>]
type IteratorStateMachineAttribute = class
    inherit StateMachineAttribute

Public NotInheritable Class IteratorStateMachineAttribute
Inherits StateMachineAttribute

继承

Object

Attribute

StateMachineAttribute

IteratorStateMachineAttribute

属性

AttributeUsageAttribute SerializableAttribute

示例

以下示例演示如何确定方法是否为迭代器方法。 在此示例中， IsIteratorMethod 执行以下步骤：

• 使用 /> 获取方法名称的对象。

• Type使用 GetType 运算符获取属性的对象。

• 使用 MethodInfo.GetCustomAttribute.. 获取方法和属性类型的属性对象。 如果 GetCustomAttribute 返回 Nothing （Visual Basic），则方法不包含该属性。

Imports System.Collections.Generic
Imports System.Reflection
Imports System.Threading.Tasks
Imports System.Runtime.CompilerServices


Module Module1

    ' This class is used by the code below to discover method attributes.
    Public Class TheClass
        Public Async Function AsyncMethod() As Task(Of Integer)
            Await Task.Delay(5)
            Return 1
        End Function

        Public Iterator Function IteratorMethod() As IEnumerable(Of Integer)
            Yield 1
            Yield 2
        End Function

        Public Function RegularMethod() As Integer
            Return 0
        End Function
    End Class


    Private Function IsAsyncMethod(classType As Type, methodName As String)
        ' Obtain the method with the specified name.
        Dim method As MethodInfo = classType.GetMethod(methodName)

        Dim attType As Type = GetType(AsyncStateMachineAttribute)

        Dim attrib = CType(method.GetCustomAttribute(attType), AsyncStateMachineAttribute)
        ' The above variable contains the StateMachineType property.

        Return (attrib IsNot Nothing)
    End Function

    Private Function IsIteratorMethod(classType As Type, methodName As String)
        ' Obtain the method with the specified name.
        Dim method As MethodInfo = classType.GetMethod(methodName)

        Dim attType As Type = GetType(IteratorStateMachineAttribute)

        ' Obtain the custom attribute for the method.
        ' The value returned contains the StateMachineType property.
        ' Nothing is returned if the attribute isn't present for the method.
        Dim attrib = CType(method.GetCustomAttribute(attType), IteratorStateMachineAttribute)

        Return (attrib IsNot Nothing)
    End Function

    Private Sub ShowResult(classType As Type, methodName As String)
        Console.Write((methodName & ": ").PadRight(16))

        If IsAsyncMethod(classType, methodName) Then
            Console.WriteLine("Async method")
        ElseIf IsIteratorMethod(classType, methodName) Then
            Console.WriteLine("Iterator method")
        Else
            Console.WriteLine("Regular method")
        End If

        ' Note: The IteratorStateMachineAttribute applies to Visual Basic methods
        ' but not C# methods.
    End Sub

    Sub Main()
        ShowResult(GetType(TheClass), "AsyncMethod")
        ShowResult(GetType(TheClass), "IteratorMethod")
        ShowResult(GetType(TheClass), "RegularMethod")

        Console.ReadKey()
    End Sub

    '   AsyncMethod:    Async method
    '   IteratorMethod: Iterator method
    '   RegularMethod:  Regular method

End Module

注解

不应将 IteratorStateMachine 属性应用于代码中的方法。 对于具有 迭代器修饰符 的 Visual Basic 中的方法，编译器将在它发出的 IL 中应用 IteratorStateMachine 属性。

当 Visual Basic 中的方法（MethodName）具有 Iterator 修饰符时，编译器会发出包含状态机结构的 IL。 该结构包含方法中的代码。 该 IL 还包含一个调用状态机的存根方法（MethodName）。 编译器将 IteratorStateMachine 特性添加到存根方法，以便工具能够标识相应的状态机。 在编译器的未来版本中，发出的 IL 的详细信息可能会更改。

迭代器方法通过使用 Yield （Visual Basic） 语句一次返回每个元素，对集合执行自定义迭代。

另请参阅

• AsyncStateMachineAttribute
• StateMachineType