鹰眼图在VB+MapObjects2.3中的实现(上)

<P>Map1为主视图，Map2为鹰眼图（放置全图显示的图层，并且不会改变比例），以下俩段代码可以实现鹰眼睛图的显示，但是要想在Map2中实现拖动红色的矩形框（Map1的当前显示范围）来移动Map1中的显示范围，则需要用到gdi.dll,user32。dll的知识，将在后面作详细介绍该功能。</P>
<P>而红色矩形框的作用：在主视图（Map1）中进行放大，缩小的变换操作后，在鹰眼图（Map2）中的红色矩形框则标示主视图（Map1）的当前范围。</P>
<P>Private Sub Map1_AfterLayerDraw(ByVal index As Integer, ByVal canceled As Boolean, ByVal hdc As Stdole.OLE_HANDLE)<br>  If index = 0 Then<br>     '在主视图的首图层绘制后刷新Map2来更新红线范围<br>      Map2.TrackingLayer.Refresh True<br>  End If<br>End Sub</P>
<P>Private Sub Map2_AfterTrackingLayerDraw(ByVal hdc As Stdole.OLE_HANDLE)<br>  ' 在Map2中绘制Map1的当前显示范围<br>  Dim sym As New Symbol<br>  sym.OutlineColor = moRed<br>  sym.Style = moTransparentFill<br>  Map2.DrawShape Map1.Extent, sym<br>End Sub</P>
<P>如果你看了该系列的下，则可以使用下面代码，DragDLL1是定义一个类，该类在系列下有介绍，定义位置放在该窗体代码的顶端</P>
<P>Dim DragDLL1 as  New DragDLL<br>Private Sub Map2_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)<br>  '将Map2中的窗体坐标转化为地图坐标(鹰眼图)<br>  Dim p As MapObjects2.Point<br>  Set p = Map2.ToMapPoint(X, Y)<br>  <br>  '判断点p是否在Map2的红线框架内即Map1的当前显示范围(鹰眼图)<br>  If Map1.Extent.IsPointIn(p) Then<br>    Set DragDLL1 = New DragDLL1</P>
<P>    DragDLL1 .DragStart Map1.Extent, Map2, X, Y<br>  End If<br>End Sub</P>
<P>Private Sub Map2_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)<br>  If Not DragDLL1 Is Nothing Then<br>    DragDLL1 .DragMove X, Y<br>  End If<br>End Sub</P>
<P>Private Sub Map2_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)<br>  If Not DragDLL1 Is Nothing Then<br>    Map1.Extent = DragDLL1 .DragFinish(X, Y)<br>    Set DragDLL1 = Nothing<br>  End If<br>End Sub</P>

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