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目录+前言+一、功能说明+二、如何实现+1. 继承Adorner+2. 使用Thumb+3. 实现拖动逻辑+三、完整代码+四、使用示例+五、总结+前言+我们做图像编辑工具、视频编辑工具，或者画板时，有时需要实现控件拖动功能。“

目录

• 前言
• 一、功能说明
• 二、如何实现？
• 1.继承Adorner
• 2.使用Thumb
• 3.实现拖动逻辑
• 三、完整代码
• 四、使用示例
• 总结

前言

我们做图片编辑工具、视频编辑工具、或者画板有时需要实现控件缩放功能，比如图片或图形可以拉伸放大或缩小，实现这种功能通常需要8个点，对应4条边和4个角，在wpf中通常可以使用装饰器实现。

一、功能说明

8个点方放置在控件的8个方位上，通过拖动这些点对控件进行拉伸或缩小，示意图如下：

二、如何实现？

1.继承Adorner

通过装饰器的方式添加8个点在控件上，这样既可以不影响控件布局，又可以自由摆放8点控件。通过重写方法，给装饰添加控件。必要的重写的方法如下面示例所示：

public class CanvasAdorner : Adorner { //获取装饰器的元素个数 protected override Visual GetVisualChild(int index); //指定装饰器子元素个数 protected override int VisualChildrenCount{get;} //布局，添加的子元素需要手动布局。 protected override Size ArrangeOverride(Size finalSize); }

2.使用Thumb

因为Thumb实现拖动比较容易，有相关事件获取拖动距离。在装饰器中定义8个Thumb，对应8个方位点。
示例代码如下：

//4条边 Thumb _leftThumb, _topThumb, _rightThumb, _bottomThumb; //4个角 Thumb _lefTopThumb, _rightTopThumb, _rightBottomThumb, _leftbottomThumb;

初始化

public CanvasAdorner(UIElement adornedElement) : base(adornedElement) { //初始化thumb _leftThumb = new Thumb(); _leftThumb.HorizontalAlignment = HorizontalAlignment.Left; _leftThumb.VerticalAlignment = VerticalAlignment.Center; _leftThumb.Cursor = Cursors.SizeWE; //其他略... }

3.实现拖动逻辑

在Thumb的DragDelta事件可以获取拖动距离，根据八个方位的不同计算并修改控件的大小。

private void Thumb_DragDelta(object sender, DragDeltaEventArgs e) { //1.右侧点HorizontalChange加宽 //2.左侧点HorizontalChange减宽，加左移 //3.下侧点VerticalChange加高 //4.上侧点VerticalChange减高，加上移 }

三、完整代码

代码如下：

public class CanvasAdorner : Adorner { //4条边 Thumb _leftThumb, _topThumb, _rightThumb, _bottomThumb; //4个角 Thumb _lefTopThumb, _rightTopThumb, _rightBottomThumb, _leftbottomThumb; //布局容器，如果不使用布局容器，则需要给上述8个控件布局，实现和Grid布局定位是一样的，会比较繁琐且意义不大。 Grid _grid; UIElement _adornedElement; public CanvasAdorner(UIElement adornedElement) : base(adornedElement) { _adornedElement = adornedElement; //初始化thumb _leftThumb = new Thumb(); _leftThumb.HorizontalAlignment = HorizontalAlignment.Left; _leftThumb.VerticalAlignment = VerticalAlignment.Center; _leftThumb.Cursor = Cursors.SizeWE; _topThumb = new Thumb(); _topThumb.HorizontalAlignment = HorizontalAlignment.Center; _topThumb.VerticalAlignment = VerticalAlignment.Top; _topThumb.Cursor = Cursors.SizeNS; _rightThumb = new Thumb(); _rightThumb.HorizontalAlignment = HorizontalAlignment.Right; _rightThumb.VerticalAlignment = VerticalAlignment.Center; _rightThumb.Cursor = Cursors.SizeWE; _bottomThumb = new Thumb(); _bottomThumb.HorizontalAlignment = HorizontalAlignment.Center; _bottomThumb.VerticalAlignment = VerticalAlignment.Bottom; _bottomThumb.Cursor = Cursors.SizeNS; _lefTopThumb = new Thumb(); _lefTopThumb.HorizontalAlignment = HorizontalAlignment.Left; _lefTopThumb.VerticalAlignment = VerticalAlignment.Top; _lefTopThumb.Cursor = Cursors.SizeNWSE; _rightTopThumb = new Thumb(); _rightTopThumb.HorizontalAlignment = HorizontalAlignment.Right; _rightTopThumb.VerticalAlignment = VerticalAlignment.Top; _rightTopThumb.Cursor = Cursors.SizeNESW; _rightBottomThumb = new Thumb(); _rightBottomThumb.HorizontalAlignment = HorizontalAlignment.Right; _rightBottomThumb.VerticalAlignment = VerticalAlignment.Bottom; _rightBottomThumb.Cursor = Cursors.SizeNWSE; _leftbottomThumb = new Thumb(); _leftbottomThumb.HorizontalAlignment = HorizontalAlignment.Left; _leftbottomThumb.VerticalAlignment = VerticalAlignment.Bottom; _leftbottomThumb.Cursor = Cursors.SizeNESW; _grid = new Grid(); _grid.Children.Add(_leftThumb); _grid.Children.Add(_topThumb); _grid.Children.Add(_rightThumb); _grid.Children.Add(_bottomThumb); _grid.Children.Add(_lefTopThumb); _grid.Children.Add(_rightTopThumb); _grid.Children.Add(_rightBottomThumb); _grid.Children.Add(_leftbottomThumb); AddVisualChild(_grid); foreach (Thumb thumb in _grid.Children) { thumb.Width = 16; thumb.Height = 16; thumb.Background = Brushes.Green; thumb.Template = new ControlTemplate(typeof(Thumb)) { VisualTree = GetFactory(new SolidColorBrush(Colors.White)) }; thumb.DragDelta += Thumb_DragDelta; } } protected override Visual GetVisualChild(int index) { return _grid; } protected override int VisualChildrenCount { get { return 1; } } protected override Size ArrangeOverride(Size finalSize) { //直接给grid布局，grid内部的thumb会自动布局。 _grid.Arrange(new Rect(new Point(-_leftThumb.Width / 2, -_leftThumb.Height / 2), new Size(finalSize.Width + _leftThumb.Width, finalSize.Height + _leftThumb.Height))); return finalSize; } //拖动逻辑 private void Thumb_DragDelta(object sender, DragDeltaEventArgs e) { var c = _adornedElement as FrameworkElement; var thumb = sender as FrameworkElement; double left, top, width, height; if (thumb.HorizontalAlignment == HorizontalAlignment.Left) { left =double.IsNaN( Canvas.GetLeft(c))?0: Canvas.GetLeft(c) + e.HorizontalChange; width = c.Width - e.HorizontalChange; } else { left = Canvas.GetLeft(c); width = c.Width + e.HorizontalChange; } if (thumb.VerticalAlignment == VerticalAlignment.Top) { top = double.IsNaN(Canvas.GetTop(c)) ? 0 : Canvas.GetTop(c) + e.VerticalChange; height = c.Height - e.VerticalChange; } else { top = Canvas.GetTop(c); height = c.Height + e.VerticalChange; } if (thumb.HorizontalAlignment != HorizontalAlignment.Center) { if (width >= 0) { Canvas.SetLeft(c, left); c.Width = width; } } if (thumb.VerticalAlignment != VerticalAlignment.Center) { if (height >= 0) { Canvas.SetTop(c, top); c.Height = height; } } } //thumb的样式 FrameworkElementFactory GetFactory(Brush back) { var fef = new FrameworkElementFactory(typeof(Ellipse)); fef.SetValue(Ellipse.FillProperty, back); fef.SetValue(Ellipse.StrokeProperty, new SolidColorBrush((Color)ColorConverter.ConvertFromString("#999999"))); fef.SetValue(Ellipse.StrokeThicknessProperty, (double)2); return fef; } }

四、使用示例

示例代码如下：
xaml

<Canvas Margin="20"> <Border x:Name="border" Width="200" Height="200" Background="Gray" ></Border> </Canvas>

在窗口或控件的Loaded事件中添加装饰器：
cs

private void window_Loaded(object sender, RoutedEventArgs e) { var layer = AdornerLayer.GetAdornerLayer(border); layer.Add(new CanvasAdorner(border)); }

效果预览：

总结

以上就是今天要讲的内容，本文讲述了控件缩放的方法与实现，都相对较简单，尤其是实现也是特意精简了代码，比如布局直接使用Grid控件，拖动的逻辑也是较为简化，最终呈现的效果还是比较不错的。

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