检查是否打开了图形（文件）

'Sample Code: Microsoft Visual Basic version of IsFileAlreadyOpen 
'---------------------------------------------------------------- 
      ' Declaration for APIs used by our function... 
      Private Declare Function lopen Lib "kernel32" Alias "_lopen" (ByVal 
      lpPathName As String, ByVal iReadWrite As Long) As Long 
      Private Declare Function GetLastError Lib "kernel32" () As Long 
      Private Declare Function lclose Lib "kernel32" Alias "_lclose" (ByVal 
      hFile As Long) As Long 
      Function IsFileAlreadyOpen(Filename As String) As Boolean 
         Dim hFile As Long 
         Dim lastErr As Long 
         ' Initialize file handle and error variable. 
         hFile = -1 
         lastErr = 0 
         ' Open for for read and exclusive sharing. 
         hFile = lopen(Filename, &H10) 
         ' If we couldn't open the file, get the last error. 
         If hFile = -1 Then 
            lastErr = Err.LastDllError 
         ' Make sure we close the file on success. 
         Else 
            lclose (hFile) 
         End If 
         ' Check for sharing violation error. 
         If (hFile = -1) And (lastErr = 32) Then 
            IsFileAlreadyOpen = True 
         Else 
            IsFileAlreadyOpen = False 
         End If 
      End Function

      ' Declaration for APIs used by our function...
      Private Declare Function lopen Lib "kernel32" Alias "_lopen" (ByVal lpPathName As String, ByVal iReadWrite As Long) As Long
      Private Declare Function GetLastError Lib "kernel32" () As Long
      Private Declare Function lclose Lib "kernel32" Alias "_lclose" (ByVal hFile As Long) As Long
Sub test()
IsFileAlreadyOpen ("P:\Autocad\Library\Test.dwg")
End Sub
      Function IsFileAlreadyOpen(Filename As String) As Boolean
         Dim hFile As Long
         Dim lastErr As Long
         ' Initialize file handle and error variable.
         hFile = -1
         lastErr = 0
         ' Open for for read and exclusive sharing.
         hFile = lopen(Filename, &H10)
         ' If we couldn't open the file, get the last error.
         If hFile = -1 Then
            lastErr = Err.LastDllError
         ' Make sure we close the file on success.
         Else
            lclose (hFile)
         End If
         ' Check for sharing violation error.
         If (hFile = -1) And (lastErr = 32) Then
            IsFileAlreadyOpen = True
            MsgBox Filename & " Is Already Open"
         Else
            IsFileAlreadyOpen = False
            ThisDrawing.Application.Documents.Open Filename
         End If
      End Function