Calling C# BHO methods from Javascript

Question

I'm trying to figure out how to call C# methods in my BHO object from Javascript within the page. I found numerous pages on how to do it in C++/ATL/Com such as:

Browser Helper Objects and Scripts Options

Calling BHO method from Javascript?

I have tried to follow along and implement it correctly in C#, but I can't get it to work probably due to some obvious COM problems that I have which I don't fully understand.

I am using C# 4.0.

Here are the relevant parts of the code:

using SHDocVw;
using mshtml;
using System.Runtime.InteropServices;

[ComVisible(true),
 Guid("300736C4-DCDA-4DB0-90AD-4510A12EBBC6"),
 ClassInterface(ClassInterfaceType.None),
 ProgId("My Extension")]
public class BrowserHelperObject : IObjectWithSite
{
    const int DISPATCH_PROPERTYPUT = 4;
    const int FDEX_NAME_ENSURE = 2;
    const uint LOCALE_USER_DEFAULT = 0x0400;

    WebBrowser browser;

    ...
    public void OnDocumentComplete(dynamic frame, ref dynamic url)
    {
        ...
        var window = browser.Document.parentWindow;

        int pid = 0;
        window.GetDispId("myExtension", FDEX_NAME_ENSURE, ref pid);

        System.Runtime.InteropServices.ComTypes.DISPPARAMS dispParms = new System.Runtime.InteropServices.ComTypes.DISPPARAMS();
        dispParms.cArgs = 1;
        dispParms.cNamedArgs = 0;
        dispParms.rgvarg = ???;
        dispParms.rgdispidNamedArgs = IntPtr.Zero;
        System.Runtime.InteropServices.ComTypes.EXCEPINFO einfo = new System.Runtime.InteropServices.ComTypes.EXCEPINFO();
        window.Invoke(pid, LOCALE_USER_DEFAULT, DISPATCH_PROPERTYPUT, ref dispParms, this, ref einfo);            
        ...
    }

fixedpoint · Accepted Answer · 2012-02-16 05:24:33Z

25

I hate to answer my own question, but I really feel like the community ought to know the answer because it is short, simple, and beautiful with C# 4.0 and SO many people seem to have this problem.

Make sure that you correctly expose the Browser Helper Object:

[ComVisible(true),
 Guid("DA8EA345-02AE-434E-82E9-448E3DB7629E"),
 ClassInterface(ClassInterfaceType.None), ProgId("MyExtension"),
 ComDefaultInterface(typeof(IExtension))]
public class BrowserHelperObject : IObjectWithSite, IExtension
{
    ...
    public int Foo(string s) { ... }
    ...
    public void OnDocumentComplete(dynamic frame, ref dynamic url)
    {
        ...
        dynamic window = browser.Document.parentWindow;
        IExpando windowEx = (IExpando)window;
        windowEx.AddProperty("myExtension");
        window.myExtension = this;
        ...
    }
    ...
}

And you will need a definition for your extensions:

[ComVisible(true),
 Guid("4C1D2E51-018B-4A7C-8A07-618452573E42"),
 InterfaceType(ComInterfaceType.InterfaceIsDual)]
public interface IExtension
{
    [DispId(1)]
    int Foo(string s);
    ...
}

You can access your Browser Helper Object in javascript thus:

var result = window.myExtension.Foo("bar");

or just

var result = myExtension.Foo("bar");

That's it. Stop banging your head against the wall and go celebrate!

answered Feb 16, 2012 at 5:24

fixedpoint

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8 Comments

Tirumudi Over a year ago

Don't regret for answering your own question.. Because, i)people look for answer and not for the person who answered, ii) You have an issue posted and You are able to answer it means you have worked on it.. That' seriously a good thing.. congrats....

g.pickardou Over a year ago

Hi fixedpoint. Could you post a full working prototype? I tried exactly to repro this and my window.myExtension remains 'undefined' I posted this question with my full source here

Robert Petz Over a year ago

If it's not working for you try this: the browser object needs to be an instance of 'IWebBrowser' not 'IWebBrowser2'

Amel Music Over a year ago

Probably you didn't include ComDefaultInterface(typeof(IExtension)) on your implementation class, that's why it isn't working

Kinjal Dixit Over a year ago

In my case the GUID for IExtension is different. I used C:\>reg query HKLM /s /f IExtension /d /e /c to get output like this HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Interface\{B05651CD-9B10-425E-B616-1FCD828DB3B1} and the guid is in the braces.

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Amel Music · Accepted Answer · 2015-03-09 15:49:14Z

0

Also, after you add property you need to make sure to release COM references of window and windowEx

answered Mar 9, 2015 at 15:49

Amel Music

1192 silver badges9 bronze badges

1 Comment

Usama Mohsin Over a year ago

Can you please elaborate on this.

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