使用multibinding在WPF中设置自定义附加属性

Question

我有一个MVVM WPF项目，我试图使用multiconverter设置自定义附加属性的值，应该传递DataContext（ViewModel）的属性和元素上的另一个自定义附加属性。

我可以使用xaml属性语法直接将属性绑定到viewmodel，但是我无法理解如何使用multiconverter设置附加属性的值。

<StackPanel>
    <StackPanel.Resources>
        <example:HelpTextConverter x:Key="ConvertHelpText"></example:HelpTextConverter>
    </StackPanel.Resources>

    <!-- shows binding the help text properties directly to the ViewModel's property -->
    <Border example:HelpTextProperties.HelpText="{Binding HelpText}"></Border>

    <!--how to set the HelpText attached property as the result of passing the DataContext.HelpText and the HelpTextProperties.ShowHelpText property to the HelpTextConverter?-->
    <Border>
        <example:HelpTextProperties.HelpText>
            <!--does not compile-->
        </example:HelpTextProperties.HelpText>
    </Border>

</StackPanel>

下面是代码附加属性和IMultiValueConverter的代码。

class HelpTextProperties
{
    public static readonly DependencyProperty ShowHelpTextProperty =
        DependencyProperty.RegisterAttached("ShowHelpText", typeof(bool), typeof(HelpTextProperties),
            new UIPropertyMetadata(false));

    public static bool GetShowHelpText(UIElement target)
    {
        return (bool)target.GetValue(ShowHelpTextProperty);
    }

    public static void SetShowHelpText(UIElement target, bool value)
    {
        target.SetValue(ShowHelpTextProperty, value);
    }

    public static readonly DependencyProperty HelpTextProperty =
        DependencyProperty.RegisterAttached("HelpText", typeof(LabelVM), typeof(HelpTextProperties),
        new UIPropertyMetadata(null));

    public static LabelVM GetHelpText(UIElement target)
    {
        return (LabelVM)target.GetValue(ShowHelpTextProperty);
    }

    public static void SetHelpText(UIElement target, LabelVM value)
    {
        target.SetValue(ShowHelpTextProperty, value);
    }
}

class HelpTextConverter : IMultiValueConverter
{
    /// <summary>
    /// returns the label in values[0] if values[1] is true
    /// </summary>
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        LabelVM labelVM = (LabelVM)values[0];
        if (values[0] == DependencyProperty.UnsetValue) { return null; }
        if (values[1] is bool)
        {
            if ((bool)values[1]) { return labelVM; }
        }
        return null;
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

谢谢你的尽心帮助！

Answer 1

你可以尝试这个并适应你的代码：

     <Border>
        <example:HelpTextProperties.HelpText>
            <MultiBinding Converter="{StaticResource ResourceKey=ConvertHelpText}">
                <Binding Path="HelpText"/> <!--The property that you wants, from DataContext or Dependency Property-->
                <Binding Path="ShowLabel"/> <!--Same thing, the property that you wants-->
            </MultiBinding>
        </example:HelpTextProperties.HelpText>
    </Border>

这是用于设置多重绑定转换器，但我认为您可以从“MainViewModel”或主窗口的视图模型管理此行为。 也许可能更简单，或触发。 希望这会对你有所帮助......