Return nil to indicate an error condition in a .NET LispFunction

eachy · 发表于 2013-5-27 23:35:13

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Return nil to indicate an error condition in a .NET LispFunction By Wayne Brill
  Issue
  I am implementing functionality in .NET that I am using from AutoLISP. How can I return an error condition from the .NET function?

  Solution
  One suggestion is to return nil from the .NET function using the LispDataType. If the function does return nil you could then handle that appropriately. (Or you could return an integer and respond to that value in the LISP function)
  Here is an excerpt from the AutoCAD .NET Managed Class Reference guide for the LispDataType:

Public Enum LispDataType
Angle = &H138c
DottedPair = &H139a
Double = &H1389
Int16 = &H138b
Int32 = &H1392
ListBegin = &H1398
ListEnd = &H1399
Nil = &H139b
None = &H1388
ObjectId = &H138e
Orientation = &H1390
Point2d = &H138a
Point3d = &H1391
SelectionSet = &H138f
T_atom = &H139d
Text = &H138d
Void = &H1396
End Enum

复制代码

Here is a VB example. Notice that if the entity is not selected ok, the routine returns nil.

<LispFunction("getId")>
Public Function test _
(ByVal myLispArgs As ResultBuffer) As ResultBuffer
' This example asks the user to select
' an(entity) The object id of the entity is
' returned to the calling lisp function
Dim rbfResult As ResultBuffer
Dim ed As Autodesk.AutoCAD.EditorInput.Editor
ed = Autodesk.AutoCAD.ApplicationServices. _
Application.DocumentManager. _
MdiActiveDocument.Editor
Dim prmptEntOpts As New PromptEntityOptions _
("Select Entity")
Dim prmptEntRes As PromptEntityResult
' Get the entity from the users selection
prmptEntRes = ed.GetEntity(prmptEntOpts)
' Make sure the entity was selected ok
If prmptEntRes.Status <> PromptStatus.OK Then
rbfResult = New ResultBuffer _
(New TypedValue(LispDataType.Nil))
Return rbfResult
End If
' Return the ObjectId to the Lisp function
Dim objId As ObjectId
objId = prmptEntRes.ObjectId
rbfResult = New ResultBuffer _
(New TypedValue(LispDataType.ObjectId, objId))
Return rbfResult
End Function

<LispFunction("getId")> 
Public Function test _ 
  (ByVal myLispArgs As ResultBuffer) As ResultBuffer 
    ' This example asks the user to select 
    ' an(entity) The object id of the entity is 
    ' returned to the calling lisp function 
    Dim rbfResult As ResultBuffer 
    Dim ed As Autodesk.AutoCAD.EditorInput.Editor 
    ed = Autodesk.AutoCAD.ApplicationServices. _ 
                  Application.DocumentManager. _ 
                        MdiActiveDocument.Editor 
    Dim prmptEntOpts As New PromptEntityOptions _ 
                                  ("Select Entity") 
    Dim prmptEntRes As PromptEntityResult 
    ' Get the entity from the users selection 
    prmptEntRes = ed.GetEntity(prmptEntOpts) 
    ' Make sure the entity was selected ok 
    If prmptEntRes.Status <> PromptStatus.OK Then 
        rbfResult = New ResultBuffer _ 
              (New TypedValue(LispDataType.Nil)) 
        Return rbfResult 
    End If 
    ' Return the ObjectId to the Lisp function 
    Dim objId As ObjectId 
    objId = prmptEntRes.ObjectId 
    rbfResult = New ResultBuffer _ 
      (New TypedValue(LispDataType.ObjectId, objId)) 
    Return rbfResult 
End Function

Here is a LISP function that uses the .NET function:

(defun c:testID ( / objId nilTest ent)
(setq objId (getId))
(setq nilTest (nth 0 objId))
(if (= nilTest nil)
(princ "Entity not selected")
)
(if (/= nilTest nil)
(progn
(vl-load-com);ensure COM API is available
(setq ent (vlax-ename->vla-object (nth 0 objId)));the 0 element is an ename
(vla-highlight ent :vlax-true); highlight the entity using COM call
);progn
);if
(princ)
)

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