如何实现ScrollViewer内仅单个嵌套组件响应鼠标滚轮滚动？

问题描述 #

我有一个包含多个RichTextBox的外层ScrollViewer，每个RichTextBox都显示垂直滚动条。期望实现的滚动逻辑是：

• 当RichTextBox获得焦点时，仅滚动该RichTextBox
• 未聚焦时，滚动外层ScrollViewer

但当前问题是：RichTextBox获焦时，它和外层ScrollViewer会同时滚动。原因是两者都响应PreviewMouseWheel事件，且外层ScrollViewer会先捕获事件，导致RichTextBox无法单独拦截事件。

复现代码（XAML） #

<Window x:Class="RichTextBoxMouseWheel.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="300" Width="500">
    <ScrollViewer>
        <StackPanel Orientation="Vertical">
            <RichTextBox VerticalScrollBarVisibility="Visible" Height="200" Width="400" FontSize="40">
                <FlowDocument>
                    <Paragraph>Paragraph 1</Paragraph>
                    <Paragraph>Paragraph 2</Paragraph>
                    <Paragraph>Paragraph 3</Paragraph>
                </FlowDocument>
            </RichTextBox>
            <RichTextBox VerticalScrollBarVisibility="Visible" Height="200" Width="400" FontSize="40">
                <FlowDocument>
                    <Paragraph>Paragraph 1</Paragraph>
                    <Paragraph>Paragraph 2</Paragraph>
                    <Paragraph>Paragraph 3</Paragraph>
                </FlowDocument>
            </RichTextBox>
        </StackPanel>
    </ScrollViewer>
</Window>

界面说明：窗口内包含上下两个高度为200的RichTextBox，均带有垂直滚动条，整体由ScrollViewer包裹。

解决方案 #

方法1：直接添加事件处理 #

给每个RichTextBox绑定PreviewMouseWheel事件，在事件中判断当前RichTextBox是否还能滚动，若可以则拦截事件并手动触发滚动，阻止事件传递到外层ScrollViewer。

1. 修改XAML，给RichTextBox添加事件：

<RichTextBox VerticalScrollBarVisibility="Visible" Height="200" Width="400" FontSize="40"
             PreviewMouseWheel="RichTextBox_PreviewMouseWheel">
    <!-- 内容不变 -->
</RichTextBox>

2. 在后台代码中实现事件逻辑：

private void RichTextBox_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
{
    var richTextBox = sender as RichTextBox;
    if (richTextBox == null) return;

    // 获取RichTextBox内部的ScrollViewer
    var scrollViewer = FindVisualChild<ScrollViewer>(richTextBox);
    if (scrollViewer == null) return;

    // 判断是否还能继续滚动
    bool canScrollUp = scrollViewer.VerticalOffset > 0;
    bool canScrollDown = scrollViewer.VerticalOffset < scrollViewer.ScrollableHeight;

    // 根据滚轮方向决定是否拦截事件
    if ((e.Delta > 0 && canScrollUp) || (e.Delta < 0 && canScrollDown))
    {
        e.Handled = true;
        // 手动设置滚动位置，16为默认滚动步长，可按需调整
        scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset - e.Delta / 120 * 16);
    }
}

// 辅助方法：查找可视化树中的子元素
private T FindVisualChild<T>(DependencyObject parent) where T : DependencyObject
{
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
    {
        var child = VisualTreeHelper.GetChild(parent, i);
        if (child is T tChild)
            return tChild;
        
        var result = FindVisualChild<T>(child);
        if (result != null)
            return result;
    }
    return null;
}

方法2：使用附加属性（复用性更强） #

创建一个附加行为类，无需逐个给RichTextBox绑定事件，只需在XAML中设置附加属性即可。

1. 创建附加行为类：

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

namespace RichTextBoxMouseWheel
{
    public static class RichTextBoxScrollBehavior
    {
        public static readonly DependencyProperty HandleMouseWheelProperty =
            DependencyProperty.RegisterAttached(
                "HandleMouseWheel", 
                typeof(bool), 
                typeof(RichTextBoxScrollBehavior), 
                new PropertyMetadata(false, OnHandleMouseWheelChanged));

        public static bool GetHandleMouseWheel(DependencyObject obj)
        {
            return (bool)obj.GetValue(HandleMouseWheelProperty);
        }

        public static void SetHandleMouseWheel(DependencyObject obj, bool value)
        {
            obj.SetValue(HandleMouseWheelProperty, value);
        }

        private static void OnHandleMouseWheelChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (d is RichTextBox richTextBox)
            {
                if ((bool)e.NewValue)
                {
                    richTextBox.PreviewMouseWheel += RichTextBox_PreviewMouseWheel;
                }
                else
                {
                    richTextBox.PreviewMouseWheel -= RichTextBox_PreviewMouseWheel;
                }
            }
        }

        private static void RichTextBox_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
        {
            var richTextBox = sender as RichTextBox;
            if (richTextBox == null) return;

            var scrollViewer = FindVisualChild<ScrollViewer>(richTextBox);
            if (scrollViewer == null) return;

            bool canScrollUp = scrollViewer.VerticalOffset > 0;
            bool canScrollDown = scrollViewer.VerticalOffset < scrollViewer.ScrollableHeight;

            if ((e.Delta > 0 && canScrollUp) || (e.Delta < 0 && canScrollDown))
            {
                e.Handled = true;
                scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset - e.Delta / 120 * 16);
            }
        }

        private static T FindVisualChild<T>(DependencyObject parent) where T : DependencyObject
        {
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
            {
                var child = VisualTreeHelper.GetChild(parent, i);
                if (child is T tChild)
                    return tChild;
                
                var result = FindVisualChild<T>(child);
                if (result != null)
                    return result;
            }
            return null;
        }
    }
}

2. 在XAML中引用命名空间并设置附加属性：

<Window x:Class="RichTextBoxMouseWheel.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:RichTextBoxMouseWheel"
        Title="MainWindow" Height="300" Width="500">
    <ScrollViewer>
        <StackPanel Orientation="Vertical">
            <RichTextBox VerticalScrollBarVisibility="Visible" Height="200" Width="400" FontSize="40"
                         local:RichTextBoxScrollBehavior.HandleMouseWheel="True">
                <FlowDocument>
                    <Paragraph>Paragraph 1</Paragraph>
                    <Paragraph>Paragraph 2</Paragraph>
                    <Paragraph>Paragraph 3</Paragraph>
                </FlowDocument>
            </RichTextBox>
            <RichTextBox VerticalScrollBarVisibility="Visible" Height="200" Width="400" FontSize="40"
                         local:RichTextBoxScrollBehavior.HandleMouseWheel="True">
                <FlowDocument>
                    <Paragraph>Paragraph 1</Paragraph>
                    <Paragraph>Paragraph 2</Paragraph>
                    <Paragraph>Paragraph 3</Paragraph>
                </FlowDocument>
            </RichTextBox>
        </StackPanel>
    </ScrollViewer>
</Window>

原理说明 #

默认情况下，RichTextBox内部的ScrollViewer不会将PreviewMouseWheel事件标记为已处理，导致事件会继续向上冒泡到外层ScrollViewer，引发两者同时滚动。通过上述方法，在RichTextBox的PreviewMouseWheel事件中判断是否还能继续滚动，若可以则标记事件为已处理并手动控制滚动，阻止事件传递到外层；当RichTextBox已滚到边界时，不拦截事件，让外层ScrollViewer处理滚动操作。

内容的提问来源于stack exchange，提问作者Jon Skeet