绑定GradientStop工作但报告错误

Question

下面的代码将GradientStop绑定到TemplatedParent的Background.Color属性。一切正常，但我在输出窗口中得到了一个绑定错误：

System.Windows.Data错误:2:找不到控制目标元素的FrameworkElement或FrameworkContentElement。BindingExpression:Path=Background.Color；DataItem=null；目标元素是'GradientStop‘(HashCode=6944299)；目标属性是'Color’(键入'Color')

<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
x:Class="WpfBindingTest.MainWindow"
x:Name="Window"
Title="MainWindow"
Width="100" Height="100">
<Window.Resources>
    <ControlTemplate x:Key="GradientTemplate" TargetType="{x:Type ContentControl}">
        <Border BorderThickness="1" BorderBrush="{TemplateBinding Background}">
            <Border.Background>
                <LinearGradientBrush  EndPoint="0.5,1" StartPoint="0.5,0">
                    <GradientStop Color="{Binding Path=Background.Color, 
                        RelativeSource={RelativeSource TemplatedParent}}"  Offset="1"/>
                    <GradientStop Color="White"  Offset="0"/>
                </LinearGradientBrush>
            </Border.Background>
            <ContentPresenter/>
        </Border>
    </ControlTemplate>
</Window.Resources>

<Grid x:Name="LayoutRoot">
    <ContentControl Background="Green" Template="{StaticResource GradientTemplate}" >
        <TextBlock VerticalAlignment="Center" HorizontalAlignment="Center" Text="X" />
    </ContentControl>
</Grid>
</Window>

Answer 1

我在Visual控制台输出中也有相同的错误。

一种可能的解释和解决方法是报告的这里。

基本上，如果使用返回LinearGradientBrush的转换器，则不会得到错误

代码是这样的

[ValueConversion(typeof(System.Windows.Media.Color), typeof(LinearGradientBrush))]
class GradientConverter : IValueConverter
{

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var brush = new LinearGradientBrush();
        var color = (Color)value;
        brush.StartPoint = new Point(0.5, 0);
        brush.EndPoint = new Point(0.5, 1);

        brush.GradientStops.Add(new GradientStop(Colors.White, 0));
        brush.GradientStops.Add(new GradientStop((Color)value, 1));

        return brush;
    }

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

在XAML中

<Border BorderThickness="1" BorderBrush="{TemplateBinding Background}" Background="{Binding Path=Background.Color, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource gradConv}}">