Vb.net DirectCast（错误，可为空（布尔值））错误

我从一个C#项目中提取了一些代码，并将其放入转换器中。原代码为：

(Nullable<bool>)false

我甚至编译了C#项目并在Reflector中查看了它。它给出了与上述相同的VB代码，但这会产生错误：

Value of type 'Boolean' cannot be converted to 'Boolean?'

我如何正确地投射这个

根据要求提供更多代码：

Imports System.Windows
Imports System.Windows.Controls.Primitives
Imports System.Windows.Input

Public Class VirtualToggleButton

    Public Shared ReadOnly IsCheckedProperty As DependencyProperty = DependencyProperty.RegisterAttached("IsChecked", _
            GetType(Nullable(Of Boolean)), _
            GetType(VirtualToggleButton), _
            New FrameworkPropertyMetadata(DirectCast(False, Nullable(Of Boolean)), _
             FrameworkPropertyMetadataOptions.BindsTwoWayByDefault Or _
             FrameworkPropertyMetadataOptions.Journal, _
             New PropertyChangedCallback(AddressOf OnIsCheckedChanged)))

            Public Shared Function GetIsChecked(ByVal d As DependencyObject) As Nullable(Of Boolean)
        Return DirectCast(d.GetValue(IsCheckedProperty), Nullable(Of Boolean))
    End Function

            Public Shared Sub SetIsChecked(ByVal d As DependencyObject, ByVal value As Nullable(Of Boolean))
        d.SetValue(IsCheckedProperty, value)
    End Sub

            Private Shared Sub OnIsCheckedChanged(ByVal d As DependencyObject, ByVal e As DependencyPropertyChangedEventArgs)
        Dim pseudobutton As UIElement = TryCast(d, UIElement)
        If pseudobutton IsNot Nothing Then
            Dim newValue As Nullable(Of Boolean) = DirectCast(e.NewValue, Nullable(Of Boolean))
            If newValue = True Then
                RaiseCheckedEvent(pseudobutton)
            ElseIf newValue = False Then
                RaiseUncheckedEvent(pseudobutton)
            Else
                RaiseIndeterminateEvent(pseudobutton)
            End If
        End If
    End Sub


            Public Shared ReadOnly IsThreeStateProperty As DependencyProperty = DependencyProperty.RegisterAttached("IsThreeState", _
                             GetType(Boolean), _
                             GetType(VirtualToggleButton), _
                             New FrameworkPropertyMetadata(CBool(False)))

            Public Shared Function GetIsThreeState(ByVal d As DependencyObject) As Boolean
        Return CBool(d.GetValue(IsThreeStateProperty))
    End Function

            Public Shared Sub SetIsThreeState(ByVal d As DependencyObject, ByVal value As Boolean)
        d.SetValue(IsThreeStateProperty, value)
    End Sub


            Public Shared ReadOnly IsVirtualToggleButtonProperty As DependencyProperty = DependencyProperty.RegisterAttached("IsVirtualToggleButton", _
                                 GetType(Boolean), _
                                 GetType(VirtualToggleButton), _
                                 New FrameworkPropertyMetadata(CBool(False), _
                                         New PropertyChangedCallback(AddressOf OnIsVirtualToggleButtonChanged)))

            Public Shared Function GetIsVirtualToggleButton(ByVal d As DependencyObject) As Boolean
        Return CBool(d.GetValue(IsVirtualToggleButtonProperty))
    End Function

            Public Shared Sub SetIsVirtualToggleButton(ByVal d As DependencyObject, ByVal value As Boolean)
        d.SetValue(IsVirtualToggleButtonProperty, value)
    End Sub

            Private Shared Sub OnIsVirtualToggleButtonChanged(ByVal d As DependencyObject, ByVal e As DependencyPropertyChangedEventArgs)
        Dim element As IInputElement = TryCast(d, IInputElement)
        If element IsNot Nothing Then
            If CBool(e.NewValue) Then
                AddHandler element.MouseLeftButtonDown, New MouseButtonEventHandler(AddressOf VirtualToggleButton.OnMouseLeftButtonDown)
                AddHandler element.KeyDown, New KeyEventHandler(AddressOf VirtualToggleButton.OnKeyDown)
            Else
                RemoveHandler element.MouseLeftButtonDown, New MouseButtonEventHandler(AddressOf VirtualToggleButton.OnMouseLeftButtonDown)
                RemoveHandler element.KeyDown, New KeyEventHandler(AddressOf VirtualToggleButton.OnKeyDown)
            End If
        End If
    End Sub


            Friend Shared Function RaiseCheckedEvent(ByVal target As UIElement) As RoutedEventArgs
        If target Is Nothing Then
            Return Nothing
        End If

        Dim args As New RoutedEventArgs()
        args.RoutedEvent = ToggleButton.CheckedEvent
        [RaiseEvent](target, args)
        Return args
    End Function

            Friend Shared Function RaiseUncheckedEvent(ByVal target As UIElement) As RoutedEventArgs
        If target Is Nothing Then
            Return Nothing
        End If

        Dim args As New RoutedEventArgs()
        args.RoutedEvent = ToggleButton.UncheckedEvent
        [RaiseEvent](target, args)
        Return args
    End Function

            Friend Shared Function RaiseIndeterminateEvent(ByVal target As UIElement) As RoutedEventArgs
        If target Is Nothing Then
            Return Nothing
        End If

        Dim args As New RoutedEventArgs()
        args.RoutedEvent = ToggleButton.IndeterminateEvent
        [RaiseEvent](target, args)
        Return args
    End Function


    Private Shared Sub OnMouseLeftButtonDown(ByVal sender As Object, ByVal e As MouseButtonEventArgs)
        e.Handled = True
        UpdateIsChecked(TryCast(sender, DependencyObject))
    End Sub

    Private Shared Sub OnKeyDown(ByVal sender As Object, ByVal e As KeyEventArgs)
        If e.OriginalSource Is sender Then
            If e.Key = Key.Space Then
                                    If (Keyboard.Modifiers And ModifierKeys.Alt) = ModifierKeys.Alt Then
                    Return
                End If

                UpdateIsChecked(TryCast(sender, DependencyObject))

                e.Handled = True
            ElseIf e.Key = Key.Enter AndAlso CBool(TryCast(sender, DependencyObject).GetValue(KeyboardNavigation.AcceptsReturnProperty)) Then
                UpdateIsChecked(TryCast(sender, DependencyObject))
                e.Handled = True
            End If
        End If
    End Sub

    Private Shared Sub UpdateIsChecked(ByVal d As DependencyObject)
        Dim isChecked As Nullable(Of Boolean) = GetIsChecked(d)
        If isChecked = True Then
            SetIsChecked(d, If(GetIsThreeState(d), DirectCast(Nothing, Nullable(Of Boolean)), DirectCast(False, Nullable(Of Boolean))))
        Else
            SetIsChecked(d, isChecked.HasValue)
        End If
    End Sub

    Private Shared Sub [RaiseEvent](ByVal target As DependencyObject, ByVal args As RoutedEventArgs)
        If TypeOf target Is UIElement Then
            TryCast(target, UIElement).[RaiseEvent](args)
        ElseIf TypeOf target Is ContentElement Then
            TryCast(target, ContentElement).[RaiseEvent](args)
        End If
    End Sub

End Class

---

看起来您可以删除DirectCast。从我看到的情况来看，您正在将false传递给具有布尔值的函数/方法？（或可为空的（布尔值））作为参数。VB不需要C所需的显式转换（尽管在某些情况下这不是一个坏主意）。举个简单的例子

Private Function DoSomething(byval param as Boolean?) as Boolean?
   'do something and return a Nullable(of Boolean)
End Function

DoSomething(false) 'is just fine, no DirectCast needed
DoSomething(nothing) 'is also fine
DoSomething(true) 'fine

DoSomething(DirectCast(false, Nullable(of Boolean)) 'will give you the error you described

---

作为旁注，万一它混淆了Nullable（布尔值）和Boolean？也就是说，它是一个布尔变量，可以有true、false或nothing值。

TKTS是正确的，VB通常不需要显式转换，但为了完整性，“正确”的转换是：

New Boolean?(False)

---

你能发布更多的代码吗？这样我们就可以看到还有什么其他的事情发生了，你想做什么？这句话本身并不意味着什么（至少对我来说）。这就是我所需要的！“谢谢！

New Boolean?(False)