问SciChart (C# WPF)。TextAnnotation中绑定文本属性的问题

EN

 <s:CompositeAnnotation x:Class="KernelDensity.DensityAnnotation"
         xmlns:s="http://schemas.abtsoftware.co.uk/scichart"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         Canvas.ZIndex="1" MouseDoubleClick="DensityAnnotation_OnMouseDoubleClick">
<s:CompositeAnnotation.Annotations>
    <s:BoxAnnotation x:Name="DensityBoxArea" Background="#FFBADAFF" BorderBrush ="Black" BorderThickness="1" CoordinateMode="Relative" CornerRadius="1" Width="1" Height="1" Opacity="0.5" X1="0" X2="1" Y1="0" Y2="1" >
        <s:BoxAnnotation.Template>
            <ControlTemplate TargetType="s:BoxAnnotation">
                <Border x:Name="PART_BoxAnnotationRoot"
                        Margin="{TemplateBinding Margin}"
                        Background="{TemplateBinding Background}"
                        BorderBrush="{TemplateBinding BorderBrush}"
                        BorderThickness="{TemplateBinding BorderThickness}"
                        CornerRadius="{TemplateBinding CornerRadius}">
                    <Image x:Name="DensityPlot" Width="Auto" Stretch="Fill"/>
                </Border>
            </ControlTemplate>
        </s:BoxAnnotation.Template>
    </s:BoxAnnotation>
    <s:TextAnnotation x:Name="SelectedSeriesTextAnnotation"
                      Background="Black"
                      CoordinateMode="Relative"
                      CornerRadius="3"
                      Foreground="White"
                      HorizontalAnchorPoint="Center"
                      X1="0.5"
                      Y1="0.5"
                      FontSize="14"
                      Text="{Binding SelectedSeriesTextAnnotationText}">
    </s:TextAnnotation>
</s:CompositeAnnotation.Annotations>
<s:CompositeAnnotation.ToolTip >
    <ToolTip Placement="Right">
        <TextBlock Text="{Binding SelectedSeriesTextAnnotationText}" FontSize="15" Foreground="Black"/>
    </ToolTip>
</s:CompositeAnnotation.ToolTip>
</s:CompositeAnnotation>