FileSystemObject 调用执行...太快了吗？

Question

我正在开发一个修改文件的系统 "in-place"。使用引号是因为实际过程如下：

将修改写入具有临时名称的新文件。
移动（重命名）扩展名为“.bak”的源文件
将新文件移动（重命名）为源文件的名称。
删除中间文件。

此过程涉及使用 PDFtk 修改 PDF 文件。问题是，当我运行代码时，它有时会 "skips" 一路上的某个点的一个步骤，有时会导致与未发生的先前步骤之一相关的错误。

当我使用调试器单步执行代码时，每次都一切正常。如果我在每个文件系统调用之间添加以下代码，它也可以工作。

Public Sub Wait(seconds As Integer)
Dim dTimer As Double

    dTimer = Timer
    Do While Timer < dTimer + seconds
        DoEvents
    Loop

End Sub

（来源：this VBForums post）

我真的不想这样做，因为它会增加执行时间，而且我真的不知道对于将要使用此应用程序的各种客户端来说，暂停需要多长时间 "enough" .有没有更好的方法让上述功能正常工作？也许根本不使用 FileSystemObject？

这是我正在使用的代码：

If LCase$(inputFilename) = LCase$(outputFilename) Then
        ' Saving changes to original file.
        Set fso = New FileSystemObject
        tempPath = fso.GetParentFolderName(outputFilename) & "\" & _
            Format$(Now, "mm_dd_yyyy_hh_nn_ss") & ".pdf"
        ' Create temp file
        CreateSubsetFromPDF = Shell("""" & App.Path & "\pdftk"" """ & inputFilename & _
            """ cat " & pages & " output """ & tempPath & """", vbHide)
        ' Copy temp file to actual destination, overwriting.
        fso.CopyFile tempPath, outputFilename, True
        fso.DeleteFile tempPath
End If

Answer 1

我怀疑您的问题是 shell return 在启动（或未能启动）进程后立即出现。我会建议使用 API 调用 CreateProcess 并等待至少一点时间让过程 return 得到结果。我用得够多了，我为此创建了一个方法。有时我必须等待几个小时才能使生成的程序达到运行，因此我的方法使用了无限等待。因为您只希望等待几秒钟，所以我会修改等待时间以适合您自己。等待时间就是在失败之前等待的时间。否则，它会在生成的进程完成后立即 return。

Private Type STARTUPINFO
   cb As Long
   lpReserved As String
   lpDesktop As String
   lpTitle As String
   dwX As Long
   dwY As Long
   dwXSize As Long
   dwYSize As Long
   dwXCountChars As Long
   dwYCountChars As Long
   dwFillAttribute As Long
   dwFlags As Long
   wShowWindow As Integer
   cbReserved2 As Integer
   lpReserved2 As Long
   hStdInput As Long
   hStdOutput As Long
   hStdError As Long
End Type

Private Type PROCESS_INFORMATION
    hProcess As Long
    hThread As Long
    dwProcessId As Long
    dwThreadID As Long
End Type

Private Declare Function WaitForSingleObjectEx Lib "kernel32" (ByVal hHandle As Long, ByVal dwMilliseconds As Long, ByVal bAlertable As Long) As Long
Private Declare Function GetExitCodeProcess Lib "kernel32" (ByVal hProcess As Long, lpExitCode As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Private Declare Function CreateProcessA Lib "kernel32" (ByVal lpApplicationName As String, ByVal lpCommandLine As String, ByVal _
    lpProcessAttributes As Long, ByVal lpThreadAttributes As Long, _
    ByVal bInheritHandles As Long, ByVal dwCreationFlags As Long, _
    ByVal lpEnvironment As Long, ByVal lpCurrentDirectory As String, _
    lpStartupInfo As STARTUPINFO, lpProcessInformation As _
    PROCESS_INFORMATION) As Long

Private Const INFINITE = -1&
Private Const NORMAL_PRIORITY_CLASS = &H20&
Private Const SW_SHOW = 5
Private Const STARTF_USESHOWWINDOW = &H1

Public Function ExecAndWait(ByVal Program As String, Optional ByVal Parms As Variant, _
                              Optional ByVal hStdOutput As Long) As Long
   Dim proc As PROCESS_INFORMATION
   Dim start As STARTUPINFO
   Dim RET As Long
   Dim strCommandLine As String
   Dim lExitCode As Long
   Dim lWaitTime As Long

   On Error GoTo errExecAndWait

   ' quote the commandline and parameters if necessary
   If InStr(Program, """") = 0 Then ' if quotes are found assume that any necessary quoting has already been done
      If InStr(Program, " ") > 0 Then
         'do not include any Program parms (" /parm" in the quotes
         If InStr(Program, " /") > 0 Then
            strCommandLine = Chr$(34) & Left$(Program, InStr(Program, " /") - 1) & Chr$(34) & Right$(Program, Len(Program) - InStr(Program, " /") + 1)
         Else
            strCommandLine = Chr$(34) & Program & Chr$(34)
         End If
      Else
         strCommandLine = Program
      End If
   Else
      strCommandLine = Program
   End If

   If Not IsMissing(Parms) Then
      If Len(Parms) > 0 Then
         If InStr(Program, """") = 0 Then ' if quotes are found assume that any necessary quoting has already been done
            If InStr(Parms, " ") > 0 Then
               strCommandLine = strCommandLine & " " & Chr$(34) & Parms & Chr$(34)
            Else
               strCommandLine = strCommandLine & " " & Parms
            End If
         Else
            strCommandLine = strCommandLine & " " & Parms
         End If
      End If
   End If

   start.dwFlags = STARTF_USESHOWWINDOW
   start.wShowWindow = SW_SHOW

   lWaitTime = INFINITE    'forever
   ' Initialize the STARTUPINFO structure:
   start.cb = Len(start)

   ' Start the shelled application:
   RET& = CreateProcessA(vbNullString, strCommandLine, 0&, 0&, 1&, _
                        NORMAL_PRIORITY_CLASS, 0&, vbNullString, start, proc)
   ' change the return value to 0 if the dll returned other than 0 else return the dll error
   If RET& = 0 Then   'error
      ExecAndWait = 0
      Err.Raise Err.LastDllError, strCommandLine, Translate_DLL_Error(Err.LastDllError)
   Else
      Call Sleep(2000)  ' Wait for the shelled application to get going:
      RET& = WaitForSingleObjectEx(proc.hProcess, lWaitTime, False)
      RET& = GetExitCodeProcess(proc.hProcess, lExitCode)
      ExecAndWait = RET&
      RET& = CloseHandle(proc.hProcess)
      RET& = CloseHandle(proc.hThread)
   End If

   Exit Function

errExecAndWait:
    Err.Raise Err.Number, Err.Source & ":ExecAndWait", Err.Description

End Function

FileSystemObject 调用执行...太快了吗？

FileSystemObject calls executing... too fast?

vb6