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VB Forum / General 2 / September 2004Expert required - Building C Browser Helper Object - Calling it and responding to events from VB app
Hello there, Does anyone know whether it is feasible to create a Browser Helper Object (BHO) in C / C++ (a BHO being a small extension to a web browser like IE that allows the programmer to monitor and control an instance of a web browser) that can talk to and pass on events to my VB program? For example, lets say I wanted to have a BHO that had a function which I could call from my VB program, and it would give back to the VB program a list of all the currently open web browsers URLs. Don't forget that each browser instance will have an instance of a BHO (I think) and this may add to the complexity (but correct me if I'm wrong). I do realise there are other ways of getting lists of the current URL's of all the browsers, but I need to know using BHO's. Further to that, (as an example) I would like the BHO to monitor each time the web surfer pressed a Form button element. I want the BHO to send an event message to my VB program informing of which instance of browser the was just pressed, the name of the form button element and some other details like that. Is the above scenario feasible? Any help on this matter is greatly appreciated. Kind regards Dave I've checked around a bit (research on the net, scanning through available COM references in VB, etc) and I've not found anything that may do what you want. Thinking about it I don't see how many web browsers would allow this, as it would result in a TOTAL lack of privacy for the user. Even if it was a part of any common browser it would likely be blocked by any virus scanner/firewall/spyware scanner worth its weight in shrimp. I'd suggest looking around for a "Internet Explorer COM class" or something like that. Good luck mate, but I don't like your chances. > Hello there, > [quoted text clipped - 24 lines] > > Dave > I've checked around a bit (research on the net, scanning through available > COM references in VB, etc) and I've not found anything that may do what you [quoted text clipped - 4 lines] > looking around for a "Internet Explorer COM class" or something like that. > Good luck mate, but I don't like your chances. Hi David and thanks for your comments. I know for a fact that BHO exist. If you know Google toolbar, this is an BHO. Take a look at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwebgen/html/b ho.asp But it is hard to build one in VB (it can be done, but that is not the subject of this discussion). My question is about how difficult it would be to build one in C, that can talk to my VB program. E.g. If the BHO notices a user click a form button, how can it send that event to my VB program in a reliable way. Kind regards Dave >> I've checked around a bit (research on the net, scanning through available >> COM references in VB, etc) and I've not found anything that may do what [quoted text clipped - 19 lines] >user click a form button, how can it send that event to my VB program in a >reliable way. It should not be very difficult at all, once you decide on a suitable exchange mechanism. For instance.. You can hook a VB form and gather it's messages before the form gets to them. Then define a value, say, WM_APP + 100, for a particular message. From WM_APP up to, if i recall, 0xbfff are messages that are always available to an application. So if you have defined WM_APP to flag as a URL_CHANGE event (both in the C app and the VB app of course), then you simply SendMessage that to your VB app, with lParam pointing to the buffer holding the URL on the C side. The VB app's custom WindowProc then runs through a switch, finds that it is a URL_CHANGE event and peels the String out of the buffer using CopyMemory and sticks it wherever it wants to, then return False and sinks the message from the Form. Done. Another way is if your VB app has a Multiline text window, the C side (after using FindWindow to get a handle to it) then can just send the message straight to the text window. The Text_Change event should then trigger and all should be well. There are other ways too, like using WM_COPYDATA and you could even cheat and mimic a MouseMove event, but that is getting a bit nasty. :)  SignatureRegards, Frank > I've checked around a bit (research on the net, scanning through available > COM references in VB, etc) and I've not found anything that may do what you > want. Thinking about it I don't see how many web browsers would allow this, > as it would result in a TOTAL lack of privacy for the user. Yes. And that's exactly what MS has done with IE. In the WinXP SP2 update there's apparently an addded feature to control BHOs and browser Extensions, but other than that it's a big and well-known problem that the average user is entirely unaware of. A lot of companies sneak a BHO onto the machine along with various free software. (I imagine that's probably how things like Gator work.) The only way for a user to know about it is to hand-check in the Registry. The BHO then has full access to the IE DOM. IE loads them automatically as long as the Registry settings are there. BHOs are typically used for things like targetted adverting, but theoretically there's no reason that they can't do something like change every instance of "Kerry" in a page to "Bush", or vice versa. BHOs are one of the long list of reasons that one should not use IE online. This isn't exactly the answer you're asking for but it might help: The book Visual Basic Shell Programming by J.P. Hamilton (O'Reilly) has chapters and source code for both BHOs and browser extensions. I built an Extension using his code and it wasn't hard, but it was the kind of thing that you'd never figure out without sample code. The book also explains how the whole thing works and provides sample code for accessing the IE DOM and events. > Hello there, > [quoted text clipped - 23 lines] > > Dave "mayayana" <mayaXXyana1a@mindYYspring.com> wrote in message news:x6B6d.7037 > This isn't exactly the answer you're asking for but it might help: > The book Visual Basic Shell Programming by J.P. Hamilton [quoted text clipped - 4 lines] > the whole thing works and provides sample code for accessing > the IE DOM and events. Great stuff, just ordered it. Maybe I will be able to do it in VB after all. To boot found the book on Amazon market place for £2.99 bargain! |
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