How do I display a popup from a WebBrowser in another window I created?

The web browser control supports the NewWindow event to get notified about a popup window. The Winforms wrapper however does not let you do much with it, you can only cancel the popup. The native COM wrapper permits passing back a new instance of the web browser, that instance will then be used to display the popup.

Taking advantage of this requires some work. For starters, use Project + Add Reference, Browse tab and select c:\windows\system32\shdocvw.dll. That adds a reference to the native COM interface.

Create a form that acts as the popup form. Drop a WebBrowser on it and make its code look similar to this:

public partial class Form2 : Form {
    public Form2() {
        InitializeComponent();
    }
    public WebBrowser Browser {
        get { return webBrowser1; }
    }
}

The Browser property gives access to the browser that will be used to display the web page in the popup window.

Now back to the main form. Drop a WebBrowser on it and make its code look like this:

public partial class Form1 : Form {
    public Form1() {
        InitializeComponent();
        webBrowser1.Url = new Uri("http://google.com");
    }
    SHDocVw.WebBrowser nativeBrowser;
    protected override void OnLoad(EventArgs e) {
        base.OnLoad(e);
        nativeBrowser = (SHDocVw.WebBrowser)webBrowser1.ActiveXInstance;
        nativeBrowser.NewWindow2 += nativeBrowser_NewWindow2;
    }
    protected override void OnFormClosing(FormClosingEventArgs e) {
        nativeBrowser.NewWindow2 -= nativeBrowser_NewWindow2;
        base.OnFormClosing(e);
    }

    void nativeBrowser_NewWindow2(ref object ppDisp, ref bool Cancel) {
        var popup = new Form2();
        popup.Show(this);
        ppDisp = popup.Browser.ActiveXInstance;
    }
}

The OnLoad method obtains a reference to the native COM interface, then subscribes an event handler to the NewWindow2 event. I made sure to unsubscribe that event in the FormClosing event handler, not 100% sure if that’s necessary. Better safe then sorry.

The NewWindow2 event handler is the crux, note that the first argument allows passing back an untyped reference. That should be the native browser in the popup window. So I create an instance of Form2 and Show() it. Note the argument to Show(), that ensures that the popup is an owned window. Substitute this as necessary for your app, I assume you’d want to create an MDI child window in your case.

Do beware that this event doesn’t fire for the window displayed when Javascript uses alert(). The browser doesn’t treat that window as an HTML popup and doesn’t use a browser window to display it so you cannot intercept or replace it.