绑定到转换器参数

Question

是否可以在 Silverlight 4.0 中绑定到 ConverterParameter？

例如，我想做这样的事情并将 ConverterParameter 绑定到 ViewModel 中的对象。

如果这不可能，还有其他选择吗？

<RadioButton
  Content="{Binding Path=Mode}"
  IsChecked="{Binding
    Converter={StaticResource ParameterModeToBoolConverter},
    ConverterParameter={Binding Path=DataContext.SelectedMode,ElementName=root}}"
/>

Answer 1

可以通过创建自己的 Binding 来支持与 ConverterParameter 的绑定。使用方法如下：

<RadioButton Content="{Binding Path=Mode}" 
    IsChecked="{BindingWithBindableConverterParameter Converter={StaticResource ParameterModeToBoolConverter},
    ConverterParameter={Binding Path=DataContext.SelectedMode,ElementName=root}}" />

以及实现此绑定的代码：

[ContentProperty(nameof(Binding))]
public class BindingWithBindableConverterParameter : MarkupExtension
{
    public Binding Binding { get; set; }
    public BindingMode Mode { get; set; }
    public IValueConverter Converter { get; set; }
    public Binding ConverterParameter { get; set; }

    public BindingWithBindableConverterParameter()
    { }

    public BindingWithBindableConverterParameter(string path)
    {
        Binding = new Binding(path);
    }

    public BindingWithBindableConverterParameter(Binding binding)
    {
        Binding = binding;
    }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var multiBinding = new MultiBinding();
        Binding.Mode = Mode;
        multiBinding.Bindings.Add(Binding);
        if (ConverterParameter != null)
        {
            ConverterParameter.Mode = BindingMode.OneWay;
            multiBinding.Bindings.Add(ConverterParameter);
        }
        var adapter = new MultiValueConverterAdapter
        {
            Converter = Converter
        };
        multiBinding.Converter = adapter;
        return multiBinding.ProvideValue(serviceProvider);
    }

    [ContentProperty(nameof(Converter))]
    private class MultiValueConverterAdapter : IMultiValueConverter
    {
        public IValueConverter Converter { get; set; }

        private object lastParameter;

        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            if (Converter == null) return values[0]; // Required for VS design-time
            if (values.Length > 1) lastParameter = values[1];
            return Converter.Convert(values[0], targetType, lastParameter, culture);
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            if (Converter == null) return new object[] { value }; // Required for VS design-time

            return new object[] { Converter.ConvertBack(value, targetTypes[0], lastParameter, culture) };
        }
    }
}

Answer 2

我找到了一个相关的 SO 帖子，我相信它可以回答这个问题：

WPF ValidationRule with dependency property

在我的具体示例中，我最终得到了 xaml，它在实现上述示例后看起来像这样：

<conv:BindingProxy x:Key="iconCacheHolder" Value="{Binding ElementName=This,Path=IconCache}" />
<conv:UriImageConverter  x:Key="ImageConverter">
    <conv:UriImageConverter.Proxy>
        <conv:IconCacheProxy Value="{Binding Value, Source={StaticResource iconCacheHolder}}" />
    </conv:UriImageConverter.Proxy>
</conv:UriImageConverter>

Answer 3

我知道这是一个老问题，但也许这对遇到它的人有用。我找到的解决方案如下：

public class WattHoursConverter : FrameworkElement, IValueConverter
    {

        #region Unit (DependencyProperty)

        /// <summary>
        /// A description of the property.
        /// </summary>
        public string Unit
        {
            get { return (string)GetValue(UnitProperty); }
            set { SetValue(UnitProperty, value); }
        }
        public static readonly DependencyProperty UnitProperty =
            DependencyProperty.Register("Unit", typeof(string), typeof(WattHoursConverter),
            new PropertyMetadata("", new PropertyChangedCallback(OnUnitChanged)));

        private static void OnUnitChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ((WattHoursConverter)d).OnUnitChanged(e);
        }

        protected virtual void OnUnitChanged(DependencyPropertyChangedEventArgs e)
        {
        }

        #endregion


        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
// you can use the dependency property here
...
}
}

在你的 xaml 中：

<UserControl.Resources>
    <converters:WattHoursConverter x:Key="WattHoursConverter" Unit="{Binding UnitPropFromDataContext}"/>
 </UserControl.Resources>
....
  <TextBlock Grid.Column="1" TextWrapping="Wrap" Text="{Binding TotalCO2, Converter={StaticResource KgToTonnesConverter}}" FontSize="13.333" />

Answer 4

另一种选择是通过创建一个自定义转换器来包装您的其他转换器并从属性中传递转换器参数来获得幻想。这个自定义转换器只要继承DependencyObject，使用一个DependencyProperty，就可以绑定。例如：

<c:ConverterParamHelper ConverterParam="{Binding ...}">

    <c:ConverterParamHelper.Converter>

        <c:RealConverter/>

    </c:ConverterParamHelper.Converter>

</c:ConverterParamHelper>

Answer 5

很遗憾，您不能绑定到 ConverterParameter。我过去使用过两个选项：不使用转换器，而是在您的 ViewModel（或您要绑定的任何东西）上创建一个属性来为您进行转换。如果您仍想走 Converter 路线，请将整个绑定对象传递给转换器，然后您可以通过这种方式进行计算。