WPF 窗体中的 Canvas 限定范围拖动 鼠标滚轴改变大小

xaml代码:

 <Canvas Name="movBg">
             <Canvas.Background>
                 <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                     <GradientStop Color="White" Offset="0" />
                     <GradientStop Color="#FFF5FF00" Offset="1" />
                 </LinearGradientBrush>
             </Canvas.Background>
             <Canvas Canvas.Top="50" Canvas.Left="50"  Height="100" HorizontalAlignment="Left" Name="mov" VerticalAlignment="Top" Width="200" MouseLeftButtonDown="mov_MouseLeftButtonDown" MouseLeftButtonUp="mov_MouseLeftButtonUp" MouseMove="mov_MouseMove" MouseWheel="mov_MouseWheel" MaxWidth="300" MaxHeight="300">
                 <Border BorderThickness="1" BorderBrush="Black" Width="{Binding ElementName=mov,Path=Width}" Height="{Binding ElementName=mov,Path=Height}" MaxWidth="{Binding ElementName=mov,Path=MaxWidth}" MaxHeight="{Binding ElementName=mov,Path=MaxHeight}"></Border>
                 <Canvas.Background>
                     <LinearGradientBrush EndPoint="1,0.5" StartPoint="0,0.5">
                         <GradientStop Color="White" Offset="0" />
                         <GradientStop Color="#FFD679F2" Offset="1" />
                     </LinearGradientBrush>
                 </Canvas.Background>
             </Canvas>
 </Canvas>  

C#代码：

 #region 拖动选区,滚轴改变大小
         //鼠标相对于被拖动的Canvas控件mov的坐标
         Point childPoint = new Point();
         //鼠标相对于作为容器的Canvas控件movBg的坐标
         Point prevPoint = new Point();  

         private void mov_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
         {
             childPoint = e.GetPosition(mov);
         }  

         private void mov_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
         {
             Canvas c = sender as Canvas;
             Rect rc = new Rect(, , movBg.ActualWidth, movBg.ActualHeight);
             Rect childRc = new Rect(Canvas.GetLeft(c), Canvas.GetTop(c), c.ActualWidth, c.ActualHeight);
             if (!rc.Contains(childRc))
             {
                 childRc = AutoResize(rc, childRc);
                 c.SetValue(Canvas.LeftProperty, childRc.Left);
                 c.SetValue(Canvas.TopProperty, childRc.Top);
                 c.Width = childRc.Width;
                 c.Height = childRc.Height;
             }
             c.ReleaseMouseCapture();
         }  

         private void mov_MouseMove(object sender, MouseEventArgs e)
         {
             if (e.LeftButton == MouseButtonState.Pressed)
             {
                 Canvas c = sender as Canvas;  

                 prevPoint = e.GetPosition(movBg);
                 double x = prevPoint.X - childPoint.X;
                 double y = prevPoint.Y - childPoint.Y;  

                 Rect rc = new Rect(, , movBg.ActualWidth, movBg.ActualHeight);
                 Rect childRc = new Rect(Canvas.GetLeft(c), Canvas.GetTop(c), c.ActualWidth, c.ActualHeight);
                 if (!rc.Contains(childRc))
                 {
                     childRc = AutoResize(rc, childRc);
                     c.SetValue(Canvas.LeftProperty, childRc.Left);
                     c.SetValue(Canvas.TopProperty, childRc.Top);
                     c.Width = childRc.Width;
                     c.Height = childRc.Height;
                     c.ReleaseMouseCapture();
                 }
                 else
                 {
                     c.SetValue(Canvas.LeftProperty, prevPoint.X - childPoint.X);
                     c.SetValue(Canvas.TopProperty, prevPoint.Y - childPoint.Y);
                     c.CaptureMouse();
                 }
             }
         }  

         private Rect AutoResize(Rect outerRc, Rect innerRc)
         {
             double with = innerRc.Width;
             double height = innerRc.Height;  

             if (innerRc.Left < outerRc.Left)
             {
                 innerRc.X = outerRc.Left + ;
                 innerRc.Width = with;
             }
             if (innerRc.Right > outerRc.Right)
             {
                 innerRc.X = outerRc.Right - with - ;
                 innerRc.Width = with;
             }
             if (innerRc.Top < outerRc.Top)
             {
                 innerRc.Y = outerRc.Top + ;
                 innerRc.Height = height;
             }
             if (innerRc.Bottom > outerRc.Bottom)
             {
                 innerRc.Y = outerRc.Bottom - height - ;
                 innerRc.Height = height;
             }
             return innerRc;
         }  

         private void mov_MouseWheel(object sender, MouseWheelEventArgs e)
         {
             double val = e.Delta * 0.001;
             double wl = mov.Width * (val / 0.12) * 0.02;
             double hl = mov.Height * (val / 0.12) * 0.02;  

             if ((Canvas.GetLeft(mov) - wl/2.0) >  && (Canvas.GetLeft(mov) + wl + mov.Width) <= movBg.ActualWidth &&
                 (Canvas.GetTop(mov) - hl/2.0) >  && (Canvas.GetTop(mov) + hl + mov.Height) <= movBg.ActualHeight &&
                 (mov.Width + wl) < mov.MaxWidth && (mov.Height + hl) < mov.MaxHeight)
             {
                 mov.SetValue(Canvas.LeftProperty, Canvas.GetLeft(mov) - wl / 2.0);
                 mov.SetValue(Canvas.TopProperty, Canvas.GetTop(mov) - hl / 2.0);
                 mov.Width += wl;
                 mov.Height += hl;  

             }
             return;
         }
         #endregion