Веб-браузер для обработки всплывающих окон в приложении

Вы правы, что WindowClosing не увольняют за Winforms WebBrowser Control, я это подтверждаю. Похоже, это давняя ошибка в коде размещения .NET WebBrowser ActiveX, которая никогда не исправлялась. Проверьте это сообщение для получения дополнительных сведений и возможного обходного пути.

Другим возможным обходным путем может быть размещение элемента управления ActiveX WebBrowser непосредственно через класс AxHost, и в этом случае WindowClosing срабатывает правильно. Пример:

С#:

using Microsoft.Win32;
using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace WebBrowserApp
{
    // MainForm

    public partial class MainForm : Form 
    {
        WebBrowser webBrowser;

        public MainForm()
        {
            InitializeComponent();
            InitBrowser();

            if (this.webBrowser.Document == null && this.webBrowser.ActiveXInstance == null)
                throw new ApplicationException ("Unable to initialize WebBrowser ActiveX control.");

            var ax = (SHDocVw.WebBrowser)this.webBrowser.ActiveXInstance;
            ax.NewWindow2 += (ref object ppDisp, ref bool Cancel) =>
            {
                var popup = new RawBrowserPopup();
                popup.Visible = true;
                ppDisp = popup.WebBrowser.ActiveXInstance;
            };

            this.Load += (s, e) =>
            {
                this.webBrowser.DocumentText = "<a target=\"_blank\" href=\"javascript:'<button onclick=\\'window.close()\\'>Close</button>'\">Go</a>";
            };
        }

        // create a WebBrowser instance
        void InitBrowser()
        {
            this.webBrowser = new WebBrowser();
            this.webBrowser.Dock = DockStyle.Fill;
            this.Controls.Add(this.webBrowser);
            this.webBrowser.Visible = true;
        }
    }

    // RawWebBrowser

    public class RawWebBrowser : AxHost
    {
        public RawWebBrowser()
            : base("8856f961-340a-11d0-a96b-00c04fd705a2")
        {
        }

        public event EventHandler Initialized;

        protected override void AttachInterfaces()
        {
            if (this.Initialized != null)
                this.Initialized(this, new EventArgs());
        }

        public object ActiveXInstance
        {
            get
            {
                return base.GetOcx();
            }
        }
    }

    // RawBrowserPopup

    public class RawBrowserPopup : Form
    {
        RawWebBrowser webBrowser;

        public RawWebBrowser WebBrowser
        {
            get { return this.webBrowser; }
        }

        public RawBrowserPopup()
        {
            this.webBrowser = new RawWebBrowser();

            this.webBrowser.Initialized += (s, e) =>
            {
                var ax = (SHDocVw.WebBrowser)this.webBrowser.ActiveXInstance;
                ax.NewWindow2 += (ref object ppDisp, ref bool Cancel) =>
                {
                    var popup = new RawBrowserPopup();
                    popup.Visible = true;
                    ppDisp = popup.WebBrowser.ActiveXInstance;
                };

                ax.WindowClosing += (bool IsChildWindow, ref bool Cancel) =>
                {
                    Cancel = true;
                    this.Close();
                };
            };

            this.webBrowser.Dock = DockStyle.Fill;
            this.Controls.Add(this.webBrowser);
            this.webBrowser.Visible = true;
        }
    }
}

VB.NET:

Public Class Form1
    Dim webBrowser As WebBrowser = New WebBrowser()

    Sub New()
        MyBase.New()
        Me.InitializeComponent()
        webBrowser.Dock = DockStyle.Fill
        Me.Controls.Add(webBrowser)
        webBrowser.Visible = True
    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.webBrowser.DocumentText = "<a target='_blank' href='javascript:""<button onclick=\""window.close()\"">Close</button>""'>Go</a>"

        Dim ActiveX As SHDocVw.WebBrowser = Me.webBrowser.ActiveXInstance
        AddHandler ActiveX.NewWindow2, AddressOf WebBrowser_ActiveX_NewWindow2
    End Sub

    Private Sub WebBrowser_ActiveX_NewWindow2(ByRef ppDisp As Object, ByRef Cancel As Boolean)
        Dim popup As RawBrowserPopup = New RawBrowserPopup()
        popup.Visible = True
        ppDisp = popup.WebBrowser.ActiveXInstance
    End Sub
End Class

Public Class RawWebBrowser
    Inherits System.Windows.Forms.AxHost

    Sub New()
        MyBase.New("8856f961-340a-11d0-a96b-00c04fd705a2")
    End Sub

    Event Initialized(sender As Object, e As EventArgs)

    Protected Overrides Sub AttachInterfaces()
        RaiseEvent Initialized(Me, New EventArgs())
    End Sub

    Public ReadOnly Property ActiveXInstance() As Object
        Get
            Return MyBase.GetOcx()
        End Get
    End Property
End Class

Public Class RawBrowserPopup
    Inherits System.Windows.Forms.Form

    Dim WithEvents rawBrowser As RawWebBrowser = New RawWebBrowser()

    Sub New()
        MyBase.New()
        rawBrowser.Dock = DockStyle.Fill
        Me.Controls.Add(rawBrowser)
        rawBrowser.Visible = True
    End Sub

    Public ReadOnly Property WebBrowser() As Object
        Get
            Return rawBrowser
        End Get
    End Property

    Private Sub rawBrowser_Initialized(sender As Object, e As EventArgs) Handles rawBrowser.Initialized
        Dim activeX As SHDocVw.WebBrowser = rawBrowser.ActiveXInstance
        AddHandler activeX.NewWindow2, AddressOf activeX_NewWindow2
        AddHandler activeX.WindowClosing, AddressOf activeX_WindowClosing
    End Sub

    Private Sub activeX_NewWindow2(ByRef ppDisp As Object, ByRef Cancel As Boolean)
        Dim popup As RawBrowserPopup = New RawBrowserPopup()
        popup.Visible = True
        ppDisp = popup.WebBrowser.ActiveXInstance
    End Sub

    Private Sub activeX_WindowClosing(IsChildWindow As Boolean, ByRef Cancel As Boolean)
        Cancel = True
        Me.Close()
    End Sub

End Class