鼠标中键（滚轮）和axMapControl之间的交互

ArcMap中对地图的浏览里，鼠标中键是一个非常重要的交互方式。它默认上滚缩小，下滚放大（与CAD相反，导致很多人不习惯），中键按下时可以对map进行平移操作。

在使用AE开发时，也希望实现类似的功能，同时，需要重载滚轮的功能，保证上滚放大，下滚缩小。

在参考（实现mapControl的滚轮缩放反效果）后，实现代码如下：

public partial class MainFrame : Form
{
IEnvelope mEnvelope = null;
IPoint mPoint = new PointClass();//缩放中心点
IPoint mousePoint = null;//鼠标点击点
IPoint startPnt = new PointClass();

public MainFrame()
{
InitializeComponent();
panel1.MouseWheel += new MouseEventHandler(panel1_MouseWheel);

axMapControl1.AutoMouseWheel = false;    //禁止axMapControl使用滚轮
mEnvelope = axMapControl1.ActiveView.Extent;
mPoint.X = (mEnvelope.XMax + mEnvelope.XMin) / 2;
mPoint.Y = (mEnvelope.YMax + mEnvelope.YMin) / 2;
}

void panel1_MouseWheel(object sender, MouseEventArgs e)
{
mousePoint = axMapControl1.ActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(e.X, e.Y);
double moveDisX = mousePoint.X - (mEnvelope.XMax + mEnvelope.XMin) / 2;
double moveDisY = mousePoint.Y - (mEnvelope.YMax + mEnvelope.YMin) / 2;
mEnvelope.CenterAt(mousePoint);
if (e.Delta > 0)
{
mEnvelope.Width = mEnvelope.Width * 0.8;
mEnvelope.Height = mEnvelope.Height * 0.8;
mPoint.X = mousePoint.X - moveDisX * 0.8;
mPoint.Y = mousePoint.Y - moveDisY * 0.8;
}
else if (e.Delta < 0)
{
mEnvelope.Width = mEnvelope.Width * 1.25;
mEnvelope.Height = mEnvelope.Height * 1.25;
mPoint.X = mousePoint.X - moveDisX * 1.2;
mPoint.Y = mousePoint.Y - moveDisY * 1.2;
}

mEnvelope.CenterAt(mPoint);
axMapControl1.ActiveView.Extent = mEnvelope;
axMapControl1.ActiveView.Refresh();
}

private void axMapControl1_OnMouseDown(object sender, ESRI.ArcGIS.Controls.IMapControlEvents2_OnMouseDownEvent e)
{
if (e.button == 4)
{//中键按下时，记住按下点的位置

startPnt.X = axMapControl1.ActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(e.x, e.y).X;
startPnt.Y = axMapControl1.ActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(e.x, e.y).Y;
mEnvelope = axMapControl1.ActiveView.Extent;
mPoint.X = (mEnvelope.XMax + mEnvelope.XMin) / 2;
mPoint.Y = (mEnvelope.YMax + mEnvelope.YMin) / 2;
}
}

private void axMapControl1_OnMouseMove(object sender, ESRI.ArcGIS.Controls.IMapControlEvents2_OnMouseMoveEvent e)
{
if(e.button==4)
{
//鼠标中键按下且拖动时
this.Cursor = System.Windows.Forms.Cursors.SizeAll;
mousePoint = axMapControl1.ActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(e.x, e.y);
double moveDisX = mousePoint.X - startPnt.X;
double moveDisY = mousePoint.Y - startPnt.Y;

mPoint.X = mPoint.X - moveDisX;
mPoint.Y = mPoint.Y - moveDisY;

mEnvelope.CenterAt(mPoint);
axMapControl1.ActiveView.Extent = mEnvelope;
axMapControl1.ActiveView.Refresh();
}
}

}