ControlTemplate LayoutTransform绑定System.Windows.Data错误2或4

Question

我正在创建一个自定义的UserControl，它将充当一个容器，在其内容后面显示一个大小大小的水印。

ControlTemplate的相关部分(下面我将给您完整的说明)是

    <TextBlock
                        Text="{TemplateBinding WatermarkText}"
                        Foreground="{TemplateBinding WatermarkBrush}"
                        HorizontalAlignment="Center"
                        VerticalAlignment="Center"
                        FontWeight="Bold">
                                <TextBlock.LayoutTransform>
                                    <RotateTransform Angle="{Binding WatermarkAngle,RelativeSource={RelativeSource AncestorType={x:Type local:WatermarkUserControl}}}"/>
                                </TextBlock.LayoutTransform>
                            </TextBlock>

我的UserControl具有WatermarkText、WatermarkBrush、WatermarkAngle和WatermarkVisibility的依赖属性(我将在下面包含这些属性)。注意，TemplateBindings for WatermarkText、WatermarkBrush和WatermarkVisibility都很好。

将TemplateBinding用于WatermarkAngle不起作用，因为TemplateBinding是一个轻量级的“绑定”，因此它不支持继承语境。我最终得到的WatermarkAngle绑定(上面)确实有效；但是报告了一个绑定错误：

System.Windows.Data错误:4:无法找到与引用'RelativeSource FindAncestor，AncestorType='redacted Nampace.WatermarkUserControl‘，AncestorLevel=’1‘绑定的源代码。BindingExpression:Path=WatermarkAngle；DataItem=null；目标元素为“RotateTransform”(HashCode=59772470)；目标属性为“角”(类型为“Double”)

那么，是否有更好的方法来避免报告错误呢？那么，考虑到绑定实际上是有效的，它为什么报告绑定错误呢？(如果我改变了值，它就反映了这一点。)

问题到此结束。以下是您需要的满足MCVE的所有部件

using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

public class WatermarkUserControl : UserControl
{
    public static readonly DependencyProperty WatermarkTextProperty =
        DependencyProperty.Register(nameof(WatermarkText), typeof(string), typeof(WatermarkUserControl), new PropertyMetadata("Watermark"));
    public static readonly DependencyProperty WatermarkBrushProperty =
        DependencyProperty.Register(nameof(WatermarkBrush), typeof(Brush), typeof(WatermarkUserControl), new PropertyMetadata(new SolidColorBrush(Colors.LightGray)));
    public static readonly DependencyProperty WatermarkAngleProperty =
        DependencyProperty.Register(nameof(WatermarkAngle), typeof(double), typeof(WatermarkUserControl), new PropertyMetadata(0d));
    public static readonly DependencyProperty WatermarkVisibilityProperty =
        DependencyProperty.Register(nameof(WatermarkVisibility), typeof(Visibility), typeof(WatermarkUserControl), new PropertyMetadata(Visibility.Visible));

    public string WatermarkText
    {
        get { return (string)GetValue(WatermarkTextProperty); }
        set { SetValue(WatermarkTextProperty, value); }
    }

    public Brush WatermarkBrush
    {
        get { return (Brush)GetValue(WatermarkBrushProperty); }
        set { SetValue(WatermarkBrushProperty, value); }
    }

    public double WatermarkAngle
    {
        get { return (double)GetValue(WatermarkAngleProperty); }
        set { SetValue(WatermarkAngleProperty, value); }
    }

    public Visibility WatermarkVisibility
    {
        get { return (Visibility)GetValue(WatermarkVisibilityProperty); }
        set { SetValue(WatermarkVisibilityProperty, value); }
    }
}

ResourceDictionary：

<Style x:Key="WatermarkUserControlBaseStyle" TargetType="local:WatermarkUserControl">
    <Setter Property="Padding" Value="0"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="local:WatermarkUserControl">
                <Grid>
                    <local:NoSizeDecorator Visibility="{TemplateBinding WatermarkVisibility}">
                        <Viewbox>
                            <TextBlock
                                Text="{TemplateBinding WatermarkText}"
                                Foreground="{TemplateBinding WatermarkBrush}"
                                HorizontalAlignment="Center"
                                VerticalAlignment="Center"
                                FontWeight="Bold">
                                <TextBlock.LayoutTransform>
                                    <RotateTransform Angle="{Binding WatermarkAngle,RelativeSource={RelativeSource AncestorType={x:Type local:WatermarkUserControl}}}"/>
                                </TextBlock.LayoutTransform>
                            </TextBlock>
                        </Viewbox>
                    </local:NoSizeDecorator>
                    <ContentPresenter Content="{TemplateBinding Content}"/>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
<Style x:Key="DraftWatermarkStyle" TargetType="local:WatermarkUserControl" BasedOn="{StaticResource WatermarkUserControlBaseStyle}">
    <Setter Property="WatermarkText" Value="DRAFT"/>
    <Setter Property="WatermarkBrush" Value="LightPink"/>
    <Setter Property="WatermarkAngle" Value="-20"/>
</Style>

NoSizeDecorator被定义为这里。

使用实例：

<local:WatermarkUserControl
    Style="{StaticResource DraftWatermarkStyle}"
    WatermarkVisibility="True">
    <StackPanel>
        <Label Content="Mr Smith"/>
        <Label Content="1 High Street"/>
        <Label Content="London"/>
    </StackPanel>
</local:WatermarkUserControl>

Answer 1

我想出了个办法。它使错误消失了，而且它似乎仍然有效，而且我还没有发现任何副作用。

我将RotateTransform声明为ControlTemplate视图框中的本地资源，然后将其绑定为StaticResource到TextBlock的LayoutTransform属性。因此问题中的Viewbox的新版本如下所示：

<Viewbox>
    <Viewbox.Resources>
        <RotateTransform x:Key="RotateWatermarkTransform" Angle="{Binding WatermarkAngle,RelativeSource={RelativeSource TemplatedParent}}"/>
    </Viewbox.Resources>

    <TextBlock
        Text="{TemplateBinding WatermarkText}"
        Foreground="{TemplateBinding WatermarkBrush}"
        HorizontalAlignment="Center"
        VerticalAlignment="Center"
        FontWeight="Bold"
        LayoutTransform="{StaticResource RotateWatermarkTransform}"/>
</Viewbox>