PRB: Cannot Simultaneously Write to Disk File and Have It Opened in ActiveX DLL (214674)

MORE INFORMATION

Steps to Reproduce Behavior

1. Create an ActiveX DLL project. Class1 is added by default.
2. From the Project menu, click Project Properties. Change the Project Name to DllFileNumber and click OK.
3. Add the following code to the General Declarations section of Class1:

   Option Explicit
   
   Private m_Fn As Integer
   
   Public Sub WriteFile(Fn As Variant)
      Write #Fn, "This is a text from the DLL."
   End Sub
   
   Public Sub OpenFile()
      m_Fn = FreeFile
      Open "C:\DllTEST.txt" For Append As #m_Fn
   End Sub
   
   Private Sub Class_Initialize()
      m_Fn = 0
   End Sub
   
   Public Property Get DLLFileNum() As Variant
      DLLFileNum = m_Fn
   End Property
   
   Public Sub CloseFile()
      If m_Fn <> 0 Then
         Close #m_Fn
         m_Fn = 0
      End If
   End Sub
   					

4. Save the ActiveX Dll project.
5. From the File menu, click Add Project and add a Standard EXE project. Form1 is added by default.
6. In the project window, set the Standard EXE project as the Start Up project by right-clicking on the project name and clicking "Set as Start Up" in the pop-up menu.
7. From the Project menu, click References and check the DllFileNumber entry.
8. Add two CommandButtons to Form1: Command1 and Command2 will be added by default. If a size larger than the default is used, the captions will be more readable.
9. Add the following code to the General Declarations section of Form1:

   Option Explicit
   
   Private Sub Command1_Click()
      Dim objvar As New DllFileNumber.Class1
      Dim sVar As String
   
      sVar = "This is text from the main program."
      objvar.OpenFile
      objvar.WriteFile objvar.DLLFileNum
      Write #objvar.DLLFileNum, sVar 'Error 52 occurs here.
      objvar.CloseFile
   End Sub
   
   Private Sub Command2_Click()
   
      Dim FileNumber As Variant
      Dim objvar As New DllFileNumber.Class1
   
      FileNumber = FreeFile
   
      Open "C:\TEST.txt" For Append As #FileNumber
      Write #FileNumber, "This is text from the main program."
   
      objvar.WriteFile FileNumber  'Error 52 occurs here.
   
      Close #FileNumber
   End Sub
   
   Private Sub Form_Load()
      Command1.Caption = "Write to a file opened in the DLL"
      Command2.Caption = "Write to a file opened in the main program"
   End Sub
   					

10. Run the program and click on the button labeled "Write to a file opened in the DLL." A Run-Time error 52 will occur on the line of Write statement. End the program.
11. Run the program again and click on the button labeled "Write to a file opened in the main program." A Run-Time error 52 will occur on the line containing the WriteFile method.

Resolution

1. Comment out the code lines containing the following comment:

   ' Error 52 occurs here.
   					

2. Run the program again and click each CommandButton. No error will occur.