at的读取字段表达式
大家好，我有一个带有属性引用的块引用。
其中一个参考是计算字段，该字段给出了多段线的面积。
这是其计算表达式：
%%).区域\f“%lu2”>%
其中2129748024是链接多段线的ID。
为了提取对象id号（2129748024），我想得到上面的表达式。我的目标是获取id号，并使用它将新属性插入到块中，该块将具有对应于同一多段线长度的计算字段。
我在www.vbaexpress上发布了这个问题。com还没有解决方案。
提前谢谢。 这段代码有点脏，很棘手，你必须把它抹掉
（抱歉格式错误）
<CommandMethod("foo")> _
Public Sub
GetFieldFromAttribute()
Dim doc As Document =
Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument
Dim db As Database =
doc.Database
Dim ed As Editor = doc.Editor
Try
Dim tab As String =
Autodesk.AutoCAD.ApplicationServices.Application.GetSystemVariable("ctab").ToString
Dim blockname As String = ed.GetString(vbLf & "Enter blockname:
").StringResult
Dim opts As PromptSelectionOptions = New
PromptSelectionOptions
opts.SingleOnly =
True
opts.MessageForRemoval = vbLf & "Select block
only"
opts.MessageForAdding = vbLf & "Select single
block"
Dim filt As SelectionFilter = New SelectionFilter({New TypedValue(0, "insert"),
New TypedValue(2, blockname), New TypedValue(410,
tab)})
Dim psr As PromptSelectionResult = ed.GetSelection(opts,
filt)
If psr.Status <> PromptStatus.OK Then Exit Sub
If psr.Value.Count <> 1 Then Exit Sub
Dim id As ObjectId = psr.Value.GetObjectIds(0)
If id.IsNull Then Exit Sub
Using tr As Transaction = db.TransactionManager.StartTransaction()
Dim obj As DBObject = tr.GetObject(psr.Value.GetObjectIds(0), OpenMode.ForRead)
If TypeOf obj Is BlockReference Then
Dim bref As BlockReference = CType(tr.GetObject(id, OpenMode.ForRead),
BlockReference)
Dim attcoll As AttributeCollection =
bref.AttributeCollection
Dim att As
AttributeReference
For Each aid As ObjectId In
attcoll
Dim aobj As DBObject = tr.GetObject(aid,
OpenMode.ForRead)
att = TryCast(DirectCast(aobj, AttributeReference),
AttributeReference)
If att Is Nothing Then Exit
Sub
If att.Tag.Equals("LENGTH", StringComparison.CurrentCultureIgnoreCase)
Then
If att.HasFields
Then
Dim fld As Field = tr.GetObject(att.GetField(),
OpenMode.ForRead)
Dim code As String =
fld.GetFieldCode
Dim pos1 As Int32 =
code.IndexOf("_ObjId")
Dim pos2 As Integer =
code.IndexOf(">%")
Dim leng1 As Integer =
"_ObjId".Length
Dim leng2 As Integer =
">%".Length
Dim idstr As String = code.Substring(pos1 + leng1 + 1, pos2 - (pos1 + leng1) -
1)
MsgBox("ID from field code: " & idstr)
Dim objId As ObjectId = New ObjectId(New IntPtr(Convert.ToInt32(idstr)))
Dim fieldchild As DBObject = tr.GetObject(objId,
OpenMode.ForRead)
If TypeOf fieldchild Is Polyline
Then
Dim poly As Polyline = DirectCast(fieldchild,
Polyline)
MsgBox("Compare:" & vbLf & "Return from attribute: " &
att.TextString & vbLf & "Return from Polyline: " &
poly.Area.ToString)
End
If
Exit
For
End
If
End If
Next
End
If
End Using
Catch ex
As
Autodesk.AutoCAD.Runtime.Exception
ed.WriteMessage(ex.Message + vbLf +
ex.StackTrace)
End Try
End Sub
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