Asynchronous File Downloads from Within VBA (Excel)

Question

I\'ve already tried using many different techniques with this... One that works pretty nicely but still ties up code when running is using the api call:

Priv         


        

Answer 1

You can do this using xmlhttp in asynchronous mode and a class to handle its events:

http://www.dailydoseofexcel.com/archives/2006/10/09/async-xmlhttp-calls/

The code there is addressing responseText, but you can adjust that to use .responseBody. Here's a (synchronous) example:

Sub FetchFile(sURL As String, sPath)
 Dim oXHTTP As Object
 Dim oStream As Object


    Set oXHTTP = CreateObject("MSXML2.XMLHTTP")
    Set oStream = CreateObject("ADODB.Stream")
    Application.StatusBar = "Fetching " & sURL & " as " & sPath
    oXHTTP.Open "GET", sURL, False
    oXHTTP.send
    With oStream
        .Type = 1 'adTypeBinary
        .Open
        .Write oXHTTP.responseBody
        .SaveToFile sPath, 2 'adSaveCreateOverWrite
        .Close
    End With
    Set oXHTTP = Nothing
    Set oStream = Nothing
    Application.StatusBar = False


End Sub

Answer 2

@TheFuzzyGiggler: +1: Thanks for sharing back. I know its an old post but perhaps I make someone happy with this addidion to TheFuzzyGigglers code (works only in classes):

I added two properties:

Private pCallBack as string
Private pCallingObject as object

Property Let Callback(ByVal CB_Function As String)
 pCallBack = CB_Function
End Property

Property Let CallingObject(set_me As Object)
 Set pCallbackObj = set_me
End Property

'and at the end of HTTP_OnResponseFinished()

CallByName pCallbackObj, pCallback, VbMethod

In my class I have

 Private EntryCollection As New Collection

 Private Sub Download(ByVal fromURL As String, ByVal toPath As String)
 Dim HTTPx As HTTPRequest
 Dim i As Integer
  Set HTTPx = New HTTPRequest
  HTTPx.SavePath = toPath
  HTTPx.Callback = "HTTPCallBack"
  HTTPx.CallingObject = Me
  HTTPx.Main fromURL
  pHTTPRequestCollection.Add HTTPx
End Sub

Sub HTTPCallBack()
Dim HTTPx As HTTPRequest
Dim i As Integer
For i = pHTTPRequestCollection.Count To 1 Step -1
  If pHTTPRequestCollection.Item(i).RequestDone Then pHTTPRequestCollection.Remove i
Next
End Sub

You could access the HTTP object from the HTTPCallBack and do many beautiful things here; the main thing is: its perfectly asynchronous now and easy to use. Hope this helps someone as the OP helped me.

I developed this further into a class: check my blog

Answer 3

Not sure if this is standard procedure or not but I didn't want to overly clutter my question so people reading it could understand it better.

But I've found an alternate solution to my question that is more in-line with what I was originally requesting. Thanks again to Tim as he set me on the right track, and his use of ADODB.Stream is a vital part of my solution.

This uses the Microsoft WinHTTP Services 5.1 .DLL that should be included with windows in one version or another, if not it is easily downloaded.

I use the following code in a class called "HTTPRequest"

Option Explicit

Private WithEvents HTTP As WinHttpRequest
Private ADStream As ADODB.Stream
Private HTTPRequest As Boolean
Private I As Double
Private SaveP As String

Sub Main(ByVal URL As String)
HTTP.Open "GET", URL, True
HTTP.send
End Sub

Private Sub Class_Initialize()
Set HTTP = New WinHttpRequest
Set ADStream = New ADODB.Stream
End Sub

Private Sub HTTP_OnError(ByVal ErrorNumber As Long, ByVal ErrorDescription As String)
Debug.Print ErrorNumber
Debug.Print ErrorDescription
End Sub


Private Sub HTTP_OnResponseFinished()
    'Tim's code Starts'
    With ADStream
        .Type = 1
        .Open
        .Write HTTP.responseBody
        .SaveToFile SaveP, 2
        .Close
    End With
    'Tim's code Ends'

HTTPRequest = True
End Sub

Private Sub HTTP_OnResponseStart(ByVal Status As Long, ByVal ContentType As String)
End Sub

Private Sub Class_Terminate()
Set HTTP = Nothing
Set ADStream = Nothing
End Sub

Property Get RequestDone() As Boolean
RequestDone = HTTPRequest
End Property

Property Let SavePath(ByVal SavePath As String)
SaveP = SavePath
End Property

The main difference between this and what Tim was describing is that WINHTTPRequest has it's own built in events which I can wrap up in one neat little class and reuse wherever. It's to me, a more elegant solution than calling the XMLHttp and then passing it to a class to wait for it.

Having it wrapped up in a class like this means I can do something along the lines of this..

Dim HTTP(10) As HTTPRequest
Dim URL(2, 10) As String
Dim I As Integer, J As Integer, Z As Integer, X As Integer

    While Not J > I
        For X = 1 To I
            If Not TypeName(HTTP(X)) = "HTTPRequest" And Not URL(2, X) = Empty Then
                Set HTTP(X) = New HTTPRequest
                HTTP(X).SavePath = URL(2, X)
                HTTP(X).Main (URL(1, X))
                Z = Z + 1
            ElseIf TypeName(HTTP(X)) = "HTTPRequest" Then
                If Not HTTP(X).RequestDone Then
                    Exit For
                Else
                    J = J + 1
                    Set HTTP(X) = Nothing
                End If
            End If
        Next
        DoEvents
    Wend 

Where I just iterate through URL() with URL(1,N) is the URL and URL(2,N) is the save location.

I admit that can probably be streamlined a bit but it gets the job done for me for now. Just tossing my solution out there for anyone interested.