Subscribing to DWebBrowserEvents2::FileDownload from WinForms WebBrowser control through the Dynamic Language Runtime (DLR).

Microsoft .NET

I will come back and add more detail to this blog at a later date, but I was helping on MSDN forums and wrote this neat example for someone. It uses the dynamic language runtime and C# 4.0 to take advantage of some of the events exposed by COM through the ActiveXInstance of the WebBrowser control. It intercepts the file download dialog when it detects you downloading an exe file and cancels the download.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Diagnostics;
using System.Reflection;

namespace WindowsFormsApplication12 {
    public partial class Form1 : Form {
        public Form1() {
            InitializeComponent();
            webBrowser1.Url = new Uri("http://www.dcomproductions.com/products/faulttrack");
        }

        /// <summary>
        /// Fires before navigation occurs in the given object (on either a window or frameset element).
        /// </summary>
        /// <param name="pDisp">Object that evaluates to the top level or frame WebBrowser object corresponding to the navigation.</param>
        /// <param name="url">String expression that evaluates to the URL to which the browser is navigating.</param>
        /// <param name="Flags">Reserved. Set to zero.</param>
        /// <param name="TargetFrameName">String expression that evaluates to the name of the frame in which the resource will be displayed, or Null if no named frame is targeted for the resource.</param>
        /// <param name="PostData">Data to send to the server if the HTTP POST transaction is being used.</param>
        /// <param name="Headers">Value that specifies the additional HTTP headers to send to the server (HTTP URLs only). The headers can specify such things as the action required of the server, the type of data being passed to the server, or a status code.</param>
        /// <param name="Cancel">Boolean value that the container can set to True to cancel the navigation operation, or to False to allow it to proceed.</param>
        private delegate void BeforeNavigate2(object pDisp, ref dynamic url, ref dynamic Flags, ref dynamic TargetFrameName, ref dynamic PostData, ref dynamic Headers, ref bool Cancel);

        /// <summary>
        /// Fires to indicate that a file download is about to occur. If a file download dialog box can be displayed, this event fires prior to the appearance of the dialog box.
        /// </summary>
        /// <param name="bActiveDocument">A Boolean that specifies whether the file is an Active Document.</param>
        /// <param name="bCancel">A Boolean that specifies whether to continue the download process and display the download dialog box.</param>
        private delegate void FileDownload(bool bActiveDocument, ref bool bCancel);

        protected override void OnLoad(EventArgs e) {
            dynamic d = webBrowser1.ActiveXInstance;
            string uri = string.Empty;

            d.BeforeNavigate2 += new BeforeNavigate2((object pDisp,
                ref dynamic url,
                ref dynamic Flags,
                ref dynamic TargetFrameName,
                ref dynamic PostData,
                ref dynamic Headers,
                ref bool Cancel) => {

                uri = url.ToString();
                Trace.WriteLine(uri);
            });

            d.FileDownload += new FileDownload((bool bActiveDocument, ref bool bCancel) => {
                bool isFile = uri.EndsWith("exe");

                if (isFile) {
                    bCancel = true;
                    Trace.Write("Canceled a file download from the DLR.");
                }
            });
        }
    }
}

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