如何将Thickness动画绑定父容器Width实现UserControl左侧滑入？

当然可以实现！先帮你排查下原来转换器没生效的可能原因：你是不是没在资源里声明转换器实例？直接写Converter=cnv:MarginWidthConverter是不对的，应该先在资源里注册<cnv:MarginWidthConverter x:Key="MarginWidthConverter"/>，然后用Converter={StaticResource MarginWidthConverter}。不过既然你想要纯XAML无转换器的方案，我给你两个更简洁的实现思路：

滑入效果用RenderTransform的TranslateTransform比操作Margin更高效，而且逻辑更清晰。这里用ObjectDataProvider来生成父容器Width的负值，完全不用自定义转换器：

<!-- 主窗口XAML -->
<Window>
    <Grid x:Name="ParentControl">
        <local:YourUserControl /> <!-- 替换为你的UserControl实际类型 -->
    </Grid>
</Window>

<!-- UserControl的XAML -->
<UserControl x:Name="ucDashboardView" xmlns:sys="clr-namespace:System;assembly=mscorlib">
    <UserControl.Resources>
        <!-- 用ObjectDataProvider生成父容器Width的负值 -->
        <ObjectDataProvider x:Key="NegativeParentWidth" 
                            ObjectType="{x:Type sys:Double}" 
                            MethodName="Parse">
            <ObjectDataProvider.MethodParameters>
                <Binding ElementName="ParentControl" 
                         Path="Width" 
                         StringFormat="-{0}"/>
            </ObjectDataProvider.MethodParameters>
        </ObjectDataProvider>
    </UserControl.Resources>

    <UserControl.RenderTransform>
        <TranslateTransform x:Name="slideTransform"/>
    </UserControl.RenderTransform>

    <UserControl.Triggers>
        <EventTrigger RoutedEvent="Loaded">
            <BeginStoryboard>
                <Storyboard>
                    <DoubleAnimation 
                        Storyboard.TargetName="slideTransform"
                        Storyboard.TargetProperty="X"
                        From="{Binding Source={StaticResource NegativeParentWidth}}"
                        To="0"
                        Duration="0:0:1"
                        EasingFunction="{StaticResource QuinticEase}"/> <!-- 可选：加缓动函数让动画更自然 -->
                </Storyboard>
            </BeginStoryboard>
        </EventTrigger>
    </UserControl.Triggers>

    <Grid Margin="50" Background="Gainsboro"/>
</UserControl>

如果你一定要操作Margin，可以用MultiBinding结合ObjectDataProvider来构造起始Thickness值，同样无需自定义转换器：

<UserControl x:Name="ucDashboardView" xmlns:sys="clr-namespace:System;assembly=mscorlib">
    <UserControl.Resources>
        <ObjectDataProvider x:Key="NegativeParentWidth" 
                            ObjectType="{x:Type sys:Double}" 
                            MethodName="Parse">
            <ObjectDataProvider.MethodParameters>
                <Binding ElementName="ParentControl" 
                         Path="Width" 
                         StringFormat="-{0}"/>
            </ObjectDataProvider.MethodParameters>
        </ObjectDataProvider>
        <ObjectDataProvider x:Key="ParentWidth" 
                            ObjectType="{x:Type sys:Double}" 
                            MethodName="Parse">
            <ObjectDataProvider.MethodParameters>
                <Binding ElementName="ParentControl" 
                         Path="Width"/>
            </ObjectDataProvider.MethodParameters>
        </ObjectDataProvider>
    </UserControl.Resources>

    <UserControl.Triggers>
        <EventTrigger RoutedEvent="Loaded">
            <BeginStoryboard>
                <Storyboard>
                    <ThicknessAnimation Storyboard.TargetProperty="Margin" Duration="0:0:1">
                        <ThicknessAnimation.From>
                            <Thickness>
                                <Binding Source="{StaticResource NegativeParentWidth}"/>
                                <Binding Path="0"/>
                                <Binding Source="{StaticResource ParentWidth}"/>
                                <Binding Path="0"/>
                            </Thickness>
                        </ThicknessAnimation.From>
                        <ThicknessAnimation.To>
                            <Thickness>0,0,0,0</Thickness>
                        </ThicknessAnimation.To>
                    </ThicknessAnimation>
                </Storyboard>
            </BeginStoryboard>
        </EventTrigger>
    </UserControl.Triggers>

    <Grid Margin="50" Background="Gainsboro"/>
</UserControl>

• 没有在XAML的资源中声明转换器实例：必须先写<cnv:MarginWidthConverter x:Key="MarginWidthConverter"/>，才能用Converter={StaticResource MarginWidthConverter}
• 转换器的命名空间引用错误：检查xmlns:cnv="clr-namespace:YourProjectNamespace"是否正确
• 绑定时机问题：UserControl加载时父容器的Width可能还未计算完成，导致转换器拿到的是0，可以改用ActualWidth或者延迟动画启动

内容的提问来源于stack exchange，提问作者5tar-Kaster