using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows;using System.Windows.Controls;using System.Windows.Data;using System.Windows.Documents;using System.Windows.Input;using System.Windows.Media;using System.Windows.Media.Imaging;using System.Windows.Navigation;using System.Windows.Shapes;namespace WPFDrawing{    /// 
    /// MainWindow.xaml 的交互逻辑    /// 
    public partial class MainWindow : Window    {        public MainWindow()        {            InitializeComponent();            Button_Click(null, null);        }        private void Button_Click(object sender, RoutedEventArgs e)        {            var pts = new PointCollection();            pts.Add(new Point() { X = 10, Y = 10 });            pts.Add(new Point() { X = 300, Y = 300 });            Visual vs = drawCanvas.Polyline(pts, Brushes.Red, 1);            drawCanvas.AddVisual(vs);        }        private void drawCanvas_MouseMove(object sender, MouseEventArgs e)        {            if (e.LeftButton == MouseButtonState.Pressed)            {                var p = e.GetPosition(null);                if (vs != null)                {                    drawCanvas.NewLine(vs, new Point() { X = 10, Y = 10 }, p);                }                Console.WriteLine(p.X + "    " + p.Y);            }        }        DrawingVisual vs = null;        private void drawCanvas_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)        {            var p = e.GetPosition(null);            Console.WriteLine(p.X + "    " + p.Y);            vs = drawCanvas.GetVisual(p);            if (vs != null)            {                Console.WriteLine("已经选中了。。。。。");            }        }    }}

using System.Collections.Generic;using System.Windows.Controls;using System.Windows.Media;using System.Windows;namespace WPFDrawing{    public class DrawingCanvas : Canvas    {        private List
      
        visuals = new List
       
        ();        //获取Visual的个数        protected override int VisualChildrenCount        {            get { return visuals.Count; }        }        //获取Visual        protected override Visual GetVisualChild(int index)        {            return visuals[index];        }        //添加Visual        public void AddVisual(Visual visual)        {            visuals.Add(visual);            base.AddVisualChild(visual);            base.AddLogicalChild(visual);        }        //删除Visual        public void RemoveVisual(Visual visual)        {            visuals.Remove(visual);            base.RemoveVisualChild(visual);            base.RemoveLogicalChild(visual);        }        //命中测试        public DrawingVisual GetVisual(Point point)        {            HitTestResult hitResult = VisualTreeHelper.HitTest(this, point);            return hitResult.VisualHit as DrawingVisual;        }        //使用DrawVisual画Polyline        public Visual Polyline(PointCollection points, Brush color, double thinkness)        {            DrawingVisual visual = new DrawingVisual();            DrawingContext dc = visual.RenderOpen();            Pen pen = new Pen(Brushes.Red, 10);            pen.Freeze();  //冻结画笔，这样能加快绘图速度            for (int i = 0; i < points.Count - 1; i++)            {                dc.DrawLine(pen, points[i], points[i + 1]);            }            dc.Close();            return visual;        }        public void NewLine(DrawingVisual visual, Point ps, Point pd)        {            DrawingContext dc = visual.RenderOpen();            Pen pen = new Pen(Brushes.Red, 2);            pen.Freeze();  //冻结画笔，这样能加快绘图速度            dc.DrawLine(pen, ps, pd);            dc.Close();        }    }}
       
      

自定义流程图线段拖动改变长短，只是提供一种思路。