具有绑定依赖属性的IValueConverter

Question

我需要根据要绑定的对象中标识的单元系统确定运行时StringFormat的某些TextBlocks绑定.

我有一个具有依赖属性的转换器,我想绑定.Bound值用于确定转换过程.

public class UnitConverter : DependencyObject, IValueConverter
{
    public static readonly DependencyProperty IsMetricProperty =
        DependencyProperty.Register("IsMetric", typeof(bool), typeof(UnitConverter), new PropertyMetadata(true, ValueChanged));

    private static void ValueChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
    {
        ((UnitConverter)source).IsMetric = (bool)e.NewValue;
    }

    public bool IsMetric
    {
        get { return (bool)this.GetValue(IsMetricProperty); }
        set { this.SetValue(IsMetricProperty, value); }
    }

    object IValueConverter.Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (IsMetric)
            return string.Format("{0:0.0}", value);
        else
            return string.Format("{0:0.000}", value);
    }

    object IValueConverter.ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

我宣布转换器

<my:UnitConverter x:Key="Units" IsMetric="{Binding Path=IsMetric}"/>

并绑定TextBlock

<TextBlock Text="{Binding Path=Breadth, Converter={StaticResource Units}}" Style="{StaticResource Values}"/>

从来没有,我收到以下错误:

System.Windows.Data错误:2:找不到目标元素的管理FrameworkElement或FrameworkContentElement.BindingExpression:路径= IsMetric; 的DataItem = NULL; target元素是'UnitConverter'(HashCode = 62641008); target属性是'IsMetric'(类型'布尔')

我想这是在我设置datacontext之前初始化,因此没有什么可以将IsMetric属性绑定到.我怎样才能达到预期的效果？

Answer 1

只要Breadth与IsMetric具有相同的数据对象的属性,你可以使用一个MultiBinding连同多值转换器:

<TextBlock>
    <TextBlock.Text>
        <MultiBinding Converter="{StaticResource UnitMultiValueConverter}">
            <Binding Path="Breadth" />
            <Binding Path="IsMetric" />
        </MultiBinding>
    </TextBlock.Text>
</TextBlock>

使用这样的转换器:

public class UnitMultiValueConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        double value = (double)values[0];
        bool isMetric = (bool)values[1];
        string format = isMetric ? "{0:0.0}" : "{0:0.000}";
        return string.Format(format, value);
    }

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

您的方法的问题是,当UnitConverter被声明为资源时,它没有DataContext,并且以后永远不会得到它.

还有一件更重要的事情:ValueChanged回调UnitConverter.IsMetric是无稽之谈.它再次设置相同的属性,刚刚更改.