Using VBA to control another program entirely

Question

I'm currently working on simplifying a process at work. It involves a Chatillon DFIS Force Meter which uses a serial connection to transmit data. The data gets sent to the Chattillon program as text and can only be saved as a .dat file. I'm trying to set up an Excel workbook that can just automatically open the program and have different commands to put the information straight into Excel. The Commands would involve changing the units, zeroing the sensor, and transmitting.

I've done some looking around and found that the Shell feature gives you access to opening the file and should help allow you to control it but I haven't found a way to call and manipulate the program through Excel.

Chatillon Program, basically buttons to click with a mouse

Answer 1

Excel and VBA can control external applications if they have a COM interface - that is to say, if you can declare the application as an object, create an instance of the object, and see its methods and attributes.

If you can possibly get hold of a COM wrapper for your program, do it that way.

If you can't... You won't enjoy doing it using I/O streams and a Windows Shell object, because command-line DOS interfaces aren't particularly friendly as a User Interface, and they are flakier than breakdancing in a pastry factory when you try to use them as an API in VBA.

Firstly, you need the 'WshShell' object exposed by the Windows Script Host Object Model. You can declare and instantiate it by late binding as shown:

Dim objWshell As Object
Set objWshell = CreateObject("WScript.Shell")

But the correct method (which will give you Intellisense drop-downs of the properties and methods) is to use the 'Tools:References...' dialog to create a reference to the parent library, which is usually found at C:\Windows\System32\wshom.ocx

You can then declare the Shell object as:

Dim objWshell As IWshRuntimeLibrary.WshShell
Set objWshell = New IWshRuntimeLibrary.WshShell

Running a command-line executable and reading the I/O streams in VBA

:

This is an example that opens a command window and runs a command-line executable, feeding it a command-line switch '-s' and a parameter encapsulated in double quotes.

Note that the executable I'm running is NOT 'regsvr32.exe' - my shell object is executing cmd.exe, and that is the source and sink of the I/O streams.

You can, of course, run your application directly. It might work. But it is very common for the output stream to lock or 'hang' your calling function and its VBA thread when you call .StdOut.ReadLine or .StdOut.ReadAll - you have been warned.

With objWshell.Exec("CMD /K")

  

       .StdIn.WriteBlankLines 3

    .StdIn.WriteLine "C:"

    .StdIn.WriteLine "CD C:\"

 

    .StdIn.WriteLine "regsvr32.exe -s " & Chr(34) & "%LIBDIR%\FXPricer.dll" & Chr(34)

    .StdIn.WriteBlankLines 1

 

    Do Until .StdOut.AtEndOfStream

        Debug.Print .StdOut.ReadLine

    Loop


     Do Until .StdErr.AtEndOfStream

        Debug.Print .StdOut.ReadLine

    Loop


    .Terminate


End With

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