代码不多，思路也很简单，

先看看效果：

简单示例，所有代码都在MainWindow.xaml和MainWindow.xaml.cs内，

Xaml代码：

<Window x:Class="WPFDemos.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:d="http://schemas.microsoft.com/expression/blend/2008"xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"xmlns:local="clr-namespace:WPFDemos"mc:Ignorable="d"x:Name="widnow"WindowStartupLocation="CenterScreen"UseLayoutRounding="True"Background="LightBlue"FontSize="16"Title="拖动" Height="500" Width="1000"><Window.Resources><ControlTemplate x:Key="template" TargetType="{x:Type Thumb}"><Grid x:Name="bg"><Grid.Background><LinearGradientBrush ><GradientStop Color="Red" Offset="0."/><GradientStop Color="Blue" Offset="0.5"/><GradientStop Color="Green" Offset="1"/></LinearGradientBrush></Grid.Background></Grid><ControlTemplate.Triggers><Trigger Property="IsDragging" Value="True"><Setter TargetName="bg" Property="Background" Value="DarkGray"/></Trigger></ControlTemplate.Triggers></ControlTemplate></Window.Resources><Grid><Canvas x:Name="canvas" Margin="0,0"><Thumb x:Name="thumb1" Canvas.Top="0" Canvas.Left="0" Width="40" Height="40" Template="{StaticResource template}" DragDelta="Thumb_DragDelta"/><Thumb x:Name="thumb2" Canvas.Top="200" Canvas.Left="200" Width="40" Height="40" Template="{StaticResource template}" DragDelta="Thumb_DragDelta"/><Path  x:Name="path" Data="M 0,0 c 200,0 100,300 300,300" Height="200" Stretch="Fill" Stroke="Green" StrokeStartLineCap="Round" StrokeEndLineCap="Round" StrokeThickness="5" Width="200" Canvas.Left="381" Canvas.Top="105" RenderTransformOrigin="0.5,0.5"><Path.RenderTransform><TransformGroup><ScaleTransform x:Name="scale" ScaleX="0"/></TransformGroup></Path.RenderTransform></Path></Canvas></Grid>
</Window>

后台代码：

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;namespace WPFDemos
{public partial class MainWindow : Window{private void UpdateThumb(){var point1 = new Point((double)thumb1.GetValue(Canvas.LeftProperty)+thumb1.Width, (double)thumb1.GetValue(Canvas.TopProperty) + thumb1.Height / 2);var point2 = new Point((double)thumb2.GetValue(Canvas.LeftProperty), (double)thumb2.GetValue(Canvas.TopProperty) + thumb2.Height / 2);path.SetValue(Canvas.LeftProperty, Math.Min(point1.X,point2.X));path.SetValue(Canvas.TopProperty, Math.Min(point1.Y,point2.Y));path.Width = Math.Abs(point1.X - point2.X);path.Height = Math.Abs(point1.Y - point2.Y);if (point1.X < point2.X){scale.ScaleX = point1.Y < point2.Y ? 1 : -1;}else{scale.ScaleX = point1.Y < point2.Y ? -1 : 1;}}public MainWindow(){InitializeComponent();UpdateThumb();}private void Thumb_DragDelta(object sender, System.Windows.Controls.Primitives.DragDeltaEventArgs e){Thumb myThumb = (Thumb)sender; double nTop = Canvas.GetTop(myThumb) + e.VerticalChange;double nLeft = Canvas.GetLeft(myThumb) + e.HorizontalChange; Canvas.SetTop(myThumb, nTop);Canvas.SetLeft(myThumb, nLeft);UpdateThumb();}}
}

好了，结束了，

效果图：