How to Update a Progress Bar While Calling a Fortran DLL from VB6

Learn how to update a progress bar while calling a Fortran DLL from VB6 using DoEvents and a timer control.

If you are developing a VB6 application that calls a numerically intensive DLL written in Fortran, you may encounter a problem with updating a progress bar while the DLL is running. The progress bar is supposed to show the user how much of the calculation has been completed, but it does not update until the DLL returns control to the VB6 application. This can make the user think that the application is frozen or not working properly.

In this article, we will explain why this problem occurs and how to fix it using DoEvents and a timer control. We will also provide some code examples and references for further reading.

Why does the progress bar not update while the DLL is running?

The reason why the progress bar does not update while the DLL is running is that the VB6 application is blocked by the DLL call and cannot process any other events, such as the timer event that updates the progress bar. The VB6 application has to wait until the DLL finishes its work and returns control to the VB6 application before it can resume its normal operation.

This is a common issue when calling external libraries or components from VB6, especially if they are computationally intensive or take a long time to execute. The VB6 application becomes unresponsive and cannot handle any user input or update the user interface.

How to fix the problem using DoEvents and a timer control?

One way to fix the problem is to use the DoEvents function and a timer control in the VB6 application. The DoEvents function allows the VB6 application to yield control to the operating system and process any pending events, such as the timer event that updates the progress bar. The timer control is used to trigger the DoEvents function periodically, for example, every second.

The basic idea is to insert a DoEvents statement inside the loop that calls the DLL, and to enable a timer control before the loop and disable it after the loop. The timer control should have a short interval, such as 1000 milliseconds, and its Timer event should contain a DoEvents statement as well. This way, the VB6 application will call the DoEvents function every second while the DLL is running, and the progress bar will be updated accordingly.

Here is an example of how to implement this solution in VB6 code:

' Declare the DLL function
Private Declare Function FortranDLL Lib \"FortranDLL.dll\" (ByVal x As Long) As Long

' Declare a global variable to store the progress
Private progress As Long

' Create a timer control named Timer1 and set its interval to 1000 milliseconds
' Create a progress bar control named ProgressBar1 and set its max value to 100

Private Sub Command1_Click()
    ' This is the button that starts the calculation
    Dim i As Long
    Dim result As Long
    
    ' Enable the timer control
    Timer1.Enabled = True
    
    ' Reset the progress variable
    progress = 0
    
    ' Loop 100 times and call the DLL function
    For i = 1 To 100
        ' Call the DLL function and store the result
        result = FortranDLL(i)
        
        ' Increment the progress variable
        progress = progress + 1
        
        ' Call the DoEvents function to process any pending events
        DoEvents
    Next i
    
    ' Disable the timer control
    Timer1.Enabled = False
    
    ' Show the final result
    MsgBox \"The final result is \" & result
End Sub

Private Sub Timer1_Timer()
    ' This is the timer event that updates the progress bar
    ' Call the DoEvents function to process any pending events
    DoEvents
    
    ' Update the progress bar value
    ProgressBar1.Value = progress
End Sub

Frequently Asked Questions (FAQs)

Question: What is DoEvents?

Answer: DoEvents is a VB6 function that allows the application to yield control to the operating system and process any pending events, such as user input, timer events, or messages from other applications. DoEvents can improve the responsiveness and user experience of the application, but it can also introduce some risks, such as reentrancy, recursion, or unexpected errors. Therefore, DoEvents should be used with caution and only when necessary.

Question: What is a timer control?

Answer: A timer control is a VB6 control that generates a Timer event at a specified interval. The timer control can be used to perform periodic tasks, such as updating the user interface, checking the status of a process, or calling a function. The timer control has two properties: Enabled and Interval. The Enabled property determines whether the timer control is active or not. The Interval property determines how often the Timer event is triggered, in milliseconds.

Question: What is a progress bar control?

Answer: A progress bar control is a VB6 control that displays a graphical indicator of the progress of a task. The progress bar control has two properties: Min and Max. The Min property determines the minimum value of the progress bar. The Max property determines the maximum value of the progress bar. The progress bar control also has a Value property that determines the current value of the progress bar. The Value property should be between the Min and Max values.

Summary

In this article, we have learned how to update a progress bar while calling a Fortran DLL from VB6 using DoEvents and a timer control. We have explained why the problem occurs and how to fix it using some VB6 code examples. We have also answered some frequently asked questions about DoEvents, timer control, and progress bar control.

We hope this article has been helpful and informative for you. If you have any questions or feedback, please feel free to leave a comment below.

Disclaimer: This article is for educational purposes only and does not constitute professional advice. The author and the publisher are not liable for any errors or omissions, or for any consequences arising from the use of the information in this article. The user is responsible for verifying the accuracy and suitability of the information before applying it to their own situation.