VBA - MS Access: Sub providing the repetitive/same results despite changing variables

Brandon Garnett
Brandon Garnett used Ask the Experts™
on
So I'm working with a PHP API you see, and when a button is clicked I want it to send an HTTP request and get the result (which is only a few words at max)

I load the onclick method up with this code:
Private Sub cmdButton_Click()
    Dim Response As String
    Dim Protocol As String
    Dim Message As String
    Response = http_Resp("http://blahblahblah.blah&API&Variable=" & Me.Variable)
    Message = Response
    MsgBox Message
    Response = ""
    Protocol = ""
    Message = ""
End Sub

Public Function http_Resp(ByVal sReq As String) As String

    Dim byteData() As Byte
    Dim XMLHTTP As Object

    Set XMLHTTP = CreateObject("MSXML2.XMLHTTP")

    XMLHTTP.Open "GET", sReq, False
    XMLHTTP.Send
    byteData = XMLHTTP.responseBody

    Set XMLHTTP = Nothing

    http_Resp = StrConv(byteData, vbUnicode)

End Function

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The first time I press said button, there is a slight (expected) delay until the message box pops up. When it does pop up, it shows the appropriate response. However, when I click the button again, there is virtually no wait time and it pops up with the exact same response.

This is troublesome because in my case: 2 consecutive calls to the API DOES result in 2 different responses.
I am certain it is not the API's fault because if I do this manually (ie, go into the browser and go to "blahblahblah.blah") I get the expected differing responses per every refresh.

The fact that the first click makes a delay and the second (or anything after) does not have a delay makes me wonder if the VBA/MS Access is just caching the result for the Sub/Function.

I'm frustrated because this is the first language I have used that flat out skips lines code. The only way I can get the next/different result is if I completely close out of MS Access and open it back up again then click said button.
What am I doing wrong?

Thanks
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Try adding a loop to wait till the page has responded.
XMLHTTP.Open "GET", sReq, False
XMLHTTP.Send
Do Until XMLHTTP.readyState = 4: DoEvents: Loop

Ron
Top Expert 2014

Commented:
I also check the status code:
    Do Until oXMLHTTP.ReadyState = 4
        DoEvents
    Loop
    
    If oXMLHTTP.Status = 200 Then
        strHTML = oXMLHTTP.responsetext
        'add your parsing/processing code here
    End If

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Jim Dettman (EE MVE)President / Owner
Most Valuable Expert 2017
Most Valuable Expert 2012

Commented:
And a little debugging help:

1. Place a STOP or breakpoint (f9 while on a line of code)
2. Execute
3. Use F8 to single step through.
4. Hover to inspect variables, or Ctrl/G to bring up debug window and then:

? <variable>

 To print it in the window.

5. F5 will continue execution from a break.

 Looks like Ron has you pointed in the right direction though.

Jim.
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Most Valuable Expert 2015
Distinguished Expert 2018

Commented:
Sounds like the page is cached.
Try sending another request (a different value of Me.Variable) and then the first again.

/gustav
President / Owner
Most Valuable Expert 2017
Most Valuable Expert 2012
Commented:
um...might need to use POST rather than a GET.

Jim.

Author

Commented:
This worked.

Why does the page cache using GET and not using POST? I have no idea.
Page caching is part of GET.  One of the reasons POST is more secure, aside from the data parameters not being in the URL string, is that it doesn't cache.

Ron

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