UrlDownloadToFile() works in Word macro but not in vb.net

Posted on 2007-04-11
Medium Priority
Last Modified: 2013-11-26
I am using urldownloadtofile() to download a file from the web to a local machine.  The coding works fine in a Word macro but does not work in vb.net. The strange thing is that it used to work and as far as I know I have not changed any of the settings. I now get
AccessVioationException was unhandled (attempted to read or write protected memory) on the line DownloadFile2 = URLDownloadToFile(0&, _    .....

The coding is:

Option Explicit On

Public Class Form1
    Private Declare Function URLDownloadToFile Lib "urlmon" Alias _
    "URLDownloadToFileA" (ByVal pCaller As Long, ByVal szURL As String, ByVal _
    szFileName As String, ByVal dwReserved As Long, ByVal lpfnCB As Long) As Long

    Private Declare Function DeleteUrlCacheEntry Lib "Wininet.dll" _
       Alias "DeleteUrlCacheEntryA" _
      (ByVal lpszUrlName As String) As Long

    Private Const ERROR_SUCCESS As Long = 0
    Private Const BINDF_GETNEWESTVERSION As Long = &H10
    Private Const INTERNET_FLAG_RELOAD As Long = &H80000000
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Call DownloadFromWeb()
    End Sub

    Sub DownloadFromWeb()
        ' DownloadFromWeb Macro
        ' Macro created 3/16/2007 by Brian O'Gorman
        Dim sSourceUrl As String
        Dim sLocalFile As String

        sSourceUrl = ""
        sLocalFile = "c:\Web Design\LIFEnet\TestText.csv"

        'Label1.Caption = sSourceUrl
        'Label2.Caption = sLocalFile

        'Attempt to delete any cached version of
        'the file. Since we're only interested in
        'nuking the file, the routine is called as
        'a sub. If the return value is requires
        '(calling as a function), DeleteUrlCacheEntry
        'returns 1 if successful, or 0 otherwise, e.g.
        '  If DeleteUrlCacheEntry(sourceUrl) = 1 Then
        '     Debug.Print "cached file found and deleted"
        '  Else
        '     Debug.Print "no cached file for " & sourceUrl
        '  End If
        'Note that the remote URL is passed as this is the
        'name the cached file is known by. This does NOT
        'delete the file from the remote server.
        Call DeleteUrlCacheEntry(sSourceUrl)

        If DownloadFile2(sSourceUrl, sLocalFile) = True Then


        End If

    End Sub

    Private Function DownloadFile2(ByVal sSourceUrl As String, _
    ByVal sLocalFile As String) As Boolean

        'Download the file. BINDF_GETNEWESTVERSION forces
        'the API to download from the specified source.
        'Passing 0& as dwReserved causes the locally-cached
        'copy to be downloaded, if available. If the API
        'returns ERROR_SUCCESS (0), DownloadFile returns True.
        DownloadFile2 = URLDownloadToFile(0&, _
                                         sSourceUrl, _
                                         sLocalFile, _
                                         BINDF_GETNEWESTVERSION, _
                                         0&) = ERROR_SUCCESS

    End Function
End Class

Would be grateful for help on this.

Question by:bogorman
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Expert Comment

ID: 18889384
Strangely, any documentation, including MSDN2 web site state that the 4th parameter for URLDownloadToFile should be 0. Please, first make your code conforming with documentation, then try again an let me know if you are still in trouble.

Author Comment

ID: 18889408
Do you mean changing the declaration to:



Expert Comment

ID: 18889502
Not exactly. The declaration is fine, however using BINDF_GETNEWESTVERSION as the 4th parameter doesn't conform to the documentation. Fix suggestion is :

DownloadFile2 = URLDownloadToFile(0&, _
                                         sSourceUrl, _
                                         sLocalFile, _
                                         0&, _
                                         0&) = ERROR_SUCCESS
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Author Comment

ID: 18889941
I now get PInvokeStackImbalance was detected

Accepted Solution

JipFromParis earned 1500 total points
ID: 18890163
Much better ;-) This is a problem with the way Interop functions is declared. I will check later.

Author Comment

ID: 19133523
Hi JipFromParis,
Di you ever find out anything more about the causes of this problem?

Author Comment

ID: 19332263
Although JipFromParis did not complete the answer to the question he did try, so I have assigned the points to him

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