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URLDownloadToFile (urlmon)
Download a file from a URL without user prompt

C# Signature:

/// <summary>
/// The URLMON library contains this function, URLDownloadToFile, which is a way
/// to download files without user prompts.  The ExecWB( _SAVEAS ) function always
/// prompts the user, even if _DONTPROMPTUSER parameter is specified, for "internet
/// security reasons".  This function gets around those reasons.
/// </summary>
/// <param name="pCaller">Pointer to caller object (AX).</param>
/// <param name="szURL">String of the URL.</param>
/// <param name="szFileName">String of the destination filename/path.</param>
/// <param name="dwReserved">[reserved].</param>
/// <param name="lpfnCB">A callback function to monitor progress or abort.</param>
/// <returns>0 for okay.</returns>
[DllImport("urlmon.dll", CharSet=CharSet.Auto, SetLastError=true)]
static extern Int32 URLDownloadToFile (
    [MarshalAs(UnmanagedType.IUnknown)] object pCaller,
    [MarshalAs(UnmanagedType.LPWStr)] string szURL,
    [MarshalAs(UnmanagedType.LPWStr)] string szFileName,
    Int32 dwReserved,
    IntPtr lpfnCB);

VB Signature:

Declare Function URLDownloadToFile  Lib "urlmon.dll" (TODO) As TODO

User-Defined Types:



This can be used in place of IWebBrowser2.ExecWB( Save-As, Dont-Prompt ) which will always prompt the user anyway. The function does not return until the transfer finishes or fails.

Tips & Tricks:

Please add some!

Sample Code:

    int response = URLDownloadToFile( null, urlStr, fileToStoreStr, 0, IntPtr.Zero );

// Here's a sample class to use a background thread to download a file, then call an optional callback

    /// <summary>
    /// spins a background thread to download the file for us
    /// </summary>
    public class DownloadFileThread
    private DownloadCompleteCallback callback;
    private string sDownloadURL;
    private string sDownloadFile;
    private Form frmCaller;

    [DllImport("URLMON.DLL", EntryPoint = "URLDownloadToFileW", SetLastError = true,
         CharSet = CharSet.Unicode, ExactSpelling = true,
         CallingConvention = CallingConvention.StdCall)]
    public static extern int URLDownloadToFile(int pCaller, string srcURL,
        string dstFile, int Reserved, int CallBack);

    public DownloadFileThread(string sURL, string sFile, DownloadCompleteCallback callbackDelegate, Form frm)
        callback = callbackDelegate;
        sDownloadURL = sURL;
        sDownloadFile = sFile;
        frmCaller = frm;

    public void ThreadProc()
        URLDownloadToFile(0, sDownloadURL, sDownloadFile, 0, 0);
        if (callback != null)
        callback(sDownloadFile, frmCaller);

// call this class with code like:

                DownloadFileThread dft = new DownloadFileThread(
                new DownloadCompleteCallback(DownloadCompleteCallback),
                Thread t = new Thread(new ThreadStart(dft.ThreadProc));

// and the callback

    private static void DownloadCompleteCallback(string sFile, Form frm)

Alternative Managed API:

Do you know one? Please contribute it!

URLDownloadToFile @msdn on MSDN

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