前天，我写了一篇“”的文章。这次，使用从Adorner继承来写一个用于图像裁切的选择框。

先看看效果：

C#代码：

// RubberbandAdorner.cs#define VISUALCHILD

using System;

using System.IO;using System.Windows;using System.Windows.Input;using System.Windows.Media;using System.Windows.Documents;

namespace PhotoDemo

{ #if VISUALCHILD    public class RubberbandAdorner : Adorner    {         private Window1 _window;        public Window1 Window { set { _window = value; } }

        private RectangleGeometry _geometry;

                private UIElement _adornedElement;

        private Rect _selectRect;

        public Rect SelectRect { get { return _selectRect; } }

        private System.Windows.Shapes.Path _rubberband;

        public System.Windows.Shapes.Path Rubberband { get { return _rubberband; } }

        protected override int VisualChildrenCount { get { return 1; } }

                private Point _anchorPoint;                        public RubberbandAdorner(UIElement adornedElement) : base(adornedElement)        {             _adornedElement = adornedElement;            _selectRect = new Rect();            _geometry = new RectangleGeometry();            _rubberband = new System.Windows.Shapes.Path();            _rubberband.Data = _geometry;            _rubberband.StrokeThickness = 1;            _rubberband.Stroke = Brushes.Yellow;            _rubberband.Opacity = .6;            _rubberband.Visibility = Visibility.Hidden;            AddVisualChild(_rubberband);

            MouseMove += new MouseEventHandler(DrawSelection);

            MouseUp += new MouseButtonEventHandler(EndSelection);        }

        protected override Size ArrangeOverride(Size size)

        {             Size finalSize = base.ArrangeOverride(size);            ((UIElement)GetVisualChild(0)).Arrange(new Rect(new Point(), finalSize));

            return finalSize;

        }

        public void StartSelection(Point anchorPoint)

        {             _anchorPoint = anchorPoint;            _selectRect.Size = new Size(10, 10);            _selectRect.Location = _anchorPoint;            _geometry.Rect = _selectRect;             if (Visibility.Visible != _rubberband.Visibility)                _rubberband.Visibility = Visibility.Visible;        }

        private void DrawSelection(object sender, MouseEventArgs e)

        {             if (e.LeftButton == MouseButtonState.Pressed)            {                 Point mousePosition = e.GetPosition(_adornedElement);

                if (mousePosition.X < _anchorPoint.X)

                    _selectRect.X = mousePosition.X;                else                    _selectRect.X = _anchorPoint.X;

                if (mousePosition.Y < _anchorPoint.Y)

                    _selectRect.Y = mousePosition.Y;                else                    _selectRect.Y = _anchorPoint.Y;

                _selectRect.Width = Math.Abs(mousePosition.X - _anchorPoint.X);

                _selectRect.Height = Math.Abs(mousePosition.Y - _anchorPoint.Y);

                _geometry.Rect = _selectRect;

                AdornerLayer layer = AdornerLayer.GetAdornerLayer(_adornedElement);                 layer.InvalidateArrange();            }        }

        private void EndSelection(object sender, MouseButtonEventArgs e)

        {             if (3 >= _selectRect.Width || 3 >= _selectRect.Height)                _rubberband.Visibility = Visibility.Hidden;            else                _window.CropButton.IsEnabled = true;

            ReleaseMouseCapture();

        }            protected override Visual GetVisualChild(int index)        {             return _rubberband;        }    }#endif

#if NoVISUALCHILD

    public class RubberbandAdorner : Adorner

    {

        private UIElement _adornedElement;

        private bool _showRect;        private Window1 _window;        SolidColorBrush _brush;        Pen _pen;        private Rect _selectRect;        public Rect SelectRect { get { return _selectRect; } set { _selectRect = value; } }        public bool ShowRect { get { return _showRect; } set { _showRect = value; } }        public Window1 Window { set { _window = value; } }

        public RubberbandAdorner(UIElement adornedElement)

            : base(adornedElement)        {             _adornedElement = adornedElement;            _selectRect = new Rect();            _brush = new SolidColorBrush();            _brush.Color = Colors.Yellow;            _brush.Opacity = .6;            _pen = new Pen();            _pen.Thickness = 2;            _pen.Brush = _brush;            _showRect = false;            MouseMove += new MouseEventHandler(DrawSelection);            MouseUp += new MouseButtonEventHandler(EndSelection);        }

        public void StartSelection(Point anchorPoint)

        {             _anchorPoint = anchorPoint;            _selectRect.Size = new Size(0, 0);            _selectRect.Location = _anchorPoint;            if (!_showRect)                _showRect = true;        }

        private void DrawSelection(object sender, MouseEventArgs e)

        {             if (e.LeftButton == MouseButtonState.Pressed)            {                 Point mousePosition = e.GetPosition(_adornedElement);                if (mousePosition.X < _anchorPoint.X)                    _selectRect.X = mousePosition.X;                else                    _selectRect.X = _anchorPoint.X;                if (mousePosition.Y < _anchorPoint.Y)                    _selectRect.Y = mousePosition.Y;                else                    _selectRect.Y = _anchorPoint.Y;                _selectRect.Width = Math.Abs(mousePosition.X - _anchorPoint.X);                _selectRect.Height = Math.Abs(mousePosition.Y - _anchorPoint.Y);                InvalidateArrange();                AdornerLayer layer = AdornerLayer.GetAdornerLayer(_adornedElement);                layer.InvalidateArrange();            }        }

        private void EndSelection(object sender, MouseButtonEventArgs e)

        {             if (3 >= _selectRect.Width || 3 >= _selectRect.Height)                ShowRect = false;            else                _window.CropButton.IsEnabled = true;            ReleaseMouseCapture();        }

        protected override void OnRender(DrawingContext drawingContext)

        {             if (_showRect)            {                 base.OnRender(drawingContext);                drawingContext.DrawRectangle(Brushes.Transparent, _pen, _selectRect);            }            else                return;        }    }#endif

}

目前的代码是画一个实线框,而且是静止的。

有待改进的地方：

1. 如果需要制作类似Photoshop中的“蚂蚁行军”效果呢？如何写程序呢？2. 如果需要制作类似Photoshop中已框选区域可移动，修改（比如：四周四角加方形手柄）呢？