c#添加事件，以xtraTabPage控件添加MouseWheel事件为例，实现图像的放大缩小

参考文章：http://blog.youkuaiyun.com/dszgf5717/article/details/12997163#

要在控件xtraTabPage上实现用鼠标滚轮控制图像大小的功能，则需要添加MouseWheel事件，而xtraTabPage控件中没有自带这个事件，所以需要手动添加这个实现来实现功能，两步完成。

1、在xxx.Designer.cs文件中的InitializeComponent()函数里添加添加事件代码。

        this.xtraTabPage3.MouseWheel += new System.Windows.Forms.MouseEventHandler(this.xtraTabPage3_MouseWheel);

2、在xxx.cs文件中添加事件实现函数。

        private void xtraTabPage3_MouseWheel(object sender, MouseEventArgs e)
        {
            base.OnMouseWheel(e);
            Matrix4D oldTo2DTransform = CalculateTo2DTransform1();
            int compare = Math.Sign(e.Delta);
            // wheel movement is forward 
            if (compare > 0)
            {
                scaleFactor *= 1.1d;
            }
            // wheel movement is backward 
            else if (compare < 0)
            {
                scaleFactor /= 1.1d;
            }
            // --- Begin of correction on the translation to zoom into mouse position.
            // Comment out this section to zoom into center of model.
            Point3D currentScreenPoint = new Point3D(e.X, e.Y, 0d);
            Point3D modelPoint = oldTo2DTransform.GetInverse().Transform(currentScreenPoint);
            Matrix4D intermediateTo2DTransform = CalculateTo2DTransform1();
            Point3D screenPoint = intermediateTo2DTransform.Transform(modelPoint);
            translation += (currentScreenPoint - screenPoint);
            // --- End of translation correction.
            CalculateTo2DTransform1();
            this.xtraTabPage3.Invalidate();
        }