将枚举值绑定到三态复选框

Question

我有以下枚举

Enum NodeStatusTypes
    Undefined
    Grant
    Deny
End Enum

我正在尝试将一个类绑定到一个列表框，以便该类的每个实例都可以 列表框中的 name 和 permission 条目绑定到文本框和三态复选框。下面的代码部分工作，如果我添加一个其 permission 属性为 Grant 的类对象，那么复选框将被选中。但是，对于 permission 为 Deny 的对象以及复选框处于“null”状态（例如 IsChecked="null"）时，我还需要取消选中该复选框权限是未定义。我几乎可以肯定问题出在 ConverterParameter 上，但我不知道如何处理。

<ListBox>
    <ListBox.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <StackPanel.Resources>
                    <l:EnumToTriStateConverter x:Key="TriConverter" />
                </StackPanel.Resources>
                <CheckBox IsThreeState="True" IsChecked="{Binding Path=Permission, Converter={StaticResource TriConverter}, ConverterParameter={x:Static l:NodeStatusTypes.Grant}}"  />
                <TextBlock Text="{Binding Path=Name}" />
                <TextBlock Text="{Binding Path=Permission}" />
            </StackPanel>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

这是每个请求的转换器类：

Public Class EnumToTriStateConverter
    Implements IValueConverter

    Public Function Convert(value As Object, targetType As System.Type, parameter As Object, culture As System.Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.Convert
        Return value.Equals(parameter)
    End Function

    Public Function ConvertBack(value As Object, targetType As System.Type, parameter As Object, culture As System.Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.ConvertBack
        Dim retVal As NodeStatusTypes = Nothing
        Select Case value
            Case Nothing
                retVal = NodeStatusTypes.Undefined
            Case True
                retVal = NodeStatusTypes.Grant
            Case False
                retVal = NodeStatusTypes.Deny
        End Select
        Return retVal
    End Function

End Class

Answer 1

正确的实现应该是这样的：

Public Function Convert(value As Object, targetType As System.Type,
                        parameter As Object,
                        culture As System.Globalization.CultureInfo) As Object
Implements System.Windows.Data.IValueConverter.Convert

    Dim retVal As Object = Nothing;
    Select Case value
        Case NodeStatusTypes.Undefined
            retVal = Nothing
        Case NodeStatusTypes.Grant
            retVal = True
        Case NodeStatusTypes.Deny
            retVal = False
    End Select

    Return retVal

End Function

转换器参数似乎没有多大意义，您可以将其从绑定中删除。