绘制图层

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Layers 集合的 AddUserDraw Layer 方法使开发人员在地图上绘制图层。当需要绘制图层时，它与激活的 DrawUserLayer 事件结合在一起使用。该方法返回新创建的 Layer 对象。用户可以绘制任意数量的图层。

如何工作

首先，添加用户绘制图层到图层集合：

Dim lyr as Layer

Set lyr = Map1.Layers.AddUserDrawLayer("My Layer", 1)

然后，设置 DrawUser Layer 事件中的代码以绘制图层。当应用程序使用 Layers 集合的 AddUserDrawLayer 方法创建了 UserDraw 图层，在窗口需要更新时，应用程序就会激活该事件。 下面是完整的示例。

' API DEFS should be declared in a separate module

Declare Function MoveToEx Lib "gdi32" Alias "MoveToEx" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, lpPoint As POINTAPI) As Long

Declare Function LineTo Lib "gdi32" Alias "LineTo" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long

Declare Function SetMapMode Lib "gdi32" Alias "SetMapMode" (ByVal hdc As Long, ByVal nMapMode As Long) As Long

Type POINTAPI

       x As Long
       y As Long

End Type

Public Const MM_TWIPS = 6

' this sets the UserDraw Layer to “My Layer” Dim lyr as Layer

Set lyr = Map1.Layers.AddUserDrawLayer("My Layer", 1)

' this example draws a line between the corners of Wyoming

Private Sub Map1_DrawUserLayer(ByVal Layer As Object, ByVal hDC As

stdole.OLE_HANDLE, ByVal hAttributeDC As stdole.OLE_HANDLE, ByVal RectFull As Object, ByVal RectInvalid As Object)

Dim pt As POINTAPI

SetMapMode hDC, MM_TWIPS

dim PX as single

dim PY as single

Dim X1 As Double, Y1 As Double, X2 As Double, Y2 As Double

X1 = -111.0542

Y1 = 45.0009

X2 = -104.0528

Y2 = 41.0018

if map1.ClipLine(X1,Y1,X2,Y2) then

mp1.ConvertCoord X, PY, X1,Y1, miMapToScreen

MoveToEx hDC, PX, -PY, pt ' win api call

map1.ConvertCoord PX, PY, X2,Y2, miMapToScreen LineTo hDC, PX, -PY ' win api call end if

End Sub

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