爲DevExpress擴展局部縮放功能

    使用devexpress 控件可以作出美觀漂亮的界面，其豐富的控件庫大多可以知足咱們平常開發的要求。但在有的方面DEVexpress仍是作得不夠完善的，好比說其圖表控件(charting)庫就不支持局部縮放功能，而dev默認提供的縮放功能實在是太差勁了，怎麼辦呢，一個圖表的縮放是其亮點之一，又不能沒有。怎麼才能實現想要的局部縮放功能呢？

    我如今想要的效果是選定圖表的局部區域，對選定的局部區域放大，同時又要保留初始的圖表使放大後的圖可以還原到初始狀態。在此將操做分爲兩個功能，一是局部放大，二是還原。實現局部放大效果的操做分解爲如下三個觸發事件，前後順序是：左鍵點擊圖表、向右下拖動鼠標移動、釋放左鍵。還原操做分解爲兩個觸發事件，前後順序是：左鍵點擊圖表，除右下方向外的其它方向脫東鼠標移動、釋放左鍵。這裏要判斷光標是否有移動，沒有位移移動就不是以上的局部放大和還原操做。實現代碼以下

 //======================================================================
//
//        Copyright (C)  
//        All rights reserved
//
//        created by 王超 at  10/12/2014 
//        email:atasas@163.com
//
//======================================================================
 
 private bool _isScale = false;//鼠標左鍵是否按下
 private object _maxX, _minX, _maxY, _minY，_maxX1, _minX1, _maxY1, _minY1；//原圖X軸和Y軸的最大和最小值以及第二座標軸（若是有）X軸和Y軸的最大和最小值
 private object _x0, _x1, _y0, _y1;
 private object _x00, _y00, _x11,_y11;
 private Point _p0 = new Point();
 private Point _p1 = new Point();
 
 //單擊左鍵
  void DevUCChart_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                _p0 = e.Location;
                SetLocationClientValue(_p0, ref  _x0, ref  _y0,ref _x00,ref _y00);
                _isScale = true;
            }
        }
        
        //將屏幕座標轉換爲圖表的座標
     void SetLocationClientValue(Point p,ref object x0,ref object y0,ref object x1,ref object y1)
        {
            try
            {
                XYDiagram diagram = this.Diagram as XYDiagram;
                DiagramCoordinates coord = diagram.PointToDiagram(p);
                switch (coord.ArgumentScaleType)
                {
                    case ScaleType.DateTime:
                        x0 = coord.DateTimeArgument;
                        break;
                    case ScaleType.Numerical:
                        x0 = coord.NumericalArgument;
                        break;
                    case ScaleType.Qualitative:
                        x0 = coord.QualitativeArgument;
                        break;
                }
                switch (coord.ValueScaleType)
                {
                    case ScaleType.DateTime:
                        y0 = coord.DateTimeValue;
                        break;
                    case ScaleType.Numerical:
                        y0 = coord.NumericalValue;
                        break;
                }
                if (diagram.GetAllAxesX().Count > 1)
                {
                    AxisValue ax = coord.GetAxisValue(diagram.GetAllAxesX()[1]);
                    switch (coord.ArgumentScaleType)
                    {
                        case ScaleType.DateTime:
                            x1 = ax.DateTimeValue;
                            break;
                        case ScaleType.Numerical:
                            x1 = ax.NumericalValue;
                            break;
                        case ScaleType.Qualitative:
                            x1 = ax.QualitativeValue;
                            break;
                    }

                }

                if (diagram.GetAllAxesY().Count > 1)
                {
                    AxisValue ax = coord.GetAxisValue(diagram.GetAllAxesY()[1]);
                    switch (coord.ValueScaleType)
                    {
                        case ScaleType.DateTime:
                            y1 = ax.DateTimeValue;
                            break;
                        case ScaleType.Numerical:
                            y1 = ax.NumericalValue;
                            break;
                    }
                }
            }
            catch
            {

            }
        }
        
        //拖動鼠標事件，繪製虛線矩形
           void DevUCChart_MouseMove(object sender, MouseEventArgs e)
        {
            if (_isScale)
            {
                Point pE = new Point(e.Location.X - this.Location.X, e.Location.Y - this.Location.Y);
                Graphics g = this.CreateGraphics();
                Pen pen = new Pen(new SolidBrush(Color.FromArgb(100, 100, 100)));
                pen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot;
                g.DrawRectangle(pen, _p0.X, _p0.Y, e.Location.X - _p0.X, e.Location.Y - _p0.Y);
            }
        }
        
        //釋放左鍵事件
        void DevUCChart_MouseUp(object sender, MouseEventArgs e)
        {
            try
            {
                if (e.Button == MouseButtons.Left)
                {
                    _p1 = e.Location;
                    SetLocationClientValue(_p1, ref  _x1, ref  _y1, ref _x11, ref _y11);
                    XYDiagram diag = (XYDiagram)this.Diagram;
                    if (_p1.X ==_p0.X && _p1.Y == _p0.Y)//沒有拖動操做
                    {
                        return;
                    }
                    if (_p1.X > _p0.X && _p1.Y > _p0.Y)//右下拖動，局部方大
                    {
                        diag.AxisX.Range.MaxValue = _x1;
                        diag.AxisX.Range.MinValue = _x0;

                        if (diag.AxisY.Range.MinValue is double)
                        {
                            double __y1 = (double)_y1;
                            double __y0 = (double)_y0;
                            diag.AxisY.Range.MaxValue = __y1 > __y0 ? __y1 : __y0;
                            diag.AxisY.Range.MinValue = __y1 > __y0 ? __y0 : __y1;
                        }

                        if (diag.GetAllAxesX().Count > 1)
                        {
                            diag.GetAllAxesX()[1].Range.MinValue = _x00;
                            diag.GetAllAxesX()[1].Range.MaxValue = _x11;
                        }

                    }
                    else//其它方向拖動，還原
                    {
                        diag.AxisX.Range.MinValue = _minX;
                        diag.AxisX.Range.MaxValue = _maxX;
                        diag.AxisY.Range.MinValue = _minY;
                        diag.AxisY.Range.MaxValue = _maxY;
                        if (diag.GetAllAxesX().Count > 1)
                        {
                            diag.GetAllAxesX()[1].Range.MinValue = _minX1;
                            diag.GetAllAxesX()[1].Range.MaxValue = _maxX1;
                        }
                        else
                        {
                            diag.GetAllAxesY()[1].Range.MinValue = _minY1;
                            diag.GetAllAxesY()[1].Range.MaxValue = _maxY1;
                        }
                    }

                }
                
            }
            catch
            { }
            finally {
                _isScale = false;
            }
        }

效果以下：

一、選定區間x軸： 2月8號到3月14號，y軸：1.4到2.5

二、局部方大效果

以上就是我實現的對devexpress控件庫圖表控件的局部縮放擴展功能，雖然仍是有點不完美，但基本上能知足個人要了。