C# wpf Canvas中实现控件拖动调整大小

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WPF拖动改变大小系列

第一节 Grid内控件拖动调整大小
第二节 Canvas内控件拖动调整大小（本章）
第三节 窗口拖动调整大小
第四节 附加属性实现拖动调整大小
第五章 拓展更多调整大小功能

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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。

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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：

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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
}

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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;}}

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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：

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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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