Sunday, June 22, 2008

your bho and your activex control can't be the same object

Frequently I see people writing a BHO, and at some point they realize they need to make a way for a webpage to call some function implemented by the BHO. The best way to do this is to expose an ActiveX control. The most common mistake I see is trying to make the ActiveX control be the same C++ object as the BHO.

This is wrong for several reasons.

It violates good coding practice.

The whole point of object level encapsulation is that each object does one thing. If your BHO is your ActiveX control, now it does two things. It may seem at first that you're really just adding a new method to your BHO, but you have to take into account all that goes along with being an ActiveX control. Implementing IDispatch, loading and dealing with the type library, implementing IObjectSafety, etc.

Your site will be wrong.

Pretty much every IE extension type--toolbands, BHOs, toolbar buttons, ActiveX controls--implements IObjectWithSite. If you make one object be two different types of extension, they will share IObjectWithSite implementations. And they all have a different IE object that is their site.

For example, a toolbar button's site will be an object in IE's toolbar code. A BHO's site is a completely different object in ieframe.dll that knows how to create and interact with a BHO. Explorer bars are sited to an object in ieframe.dll that hosts an explorer bar. And ActiveX controls are sited to an object in mshtml.dll that knows how to host ActiveX controls and implements several DOM interfaces (IHTMLElement, etc) as well.

So if you make your BHO and your ActiveX control the same object, the BHO will be instantiated first and IE will call your IObjectWithSite::SetSite() method with a pointer to one type of object. Then, when your ActiveX control is created later on, IE will call the IObjectWithSite::SetSite() method again, but this time with a different internal IE object's address. Now your BHO is broken. And debugging this sort of thing may take you a long time.

What we Learned Today

Every IE extension you implement must be it's own object, or bad things will start to happen.

Saturday, June 21, 2008

the internet explorer object cookbook

When you start writing Internet Explorer extensions, or dealing with the DOM and the Webbrowser control at all, you frequently find you have an object of type X and you need to get the corresponding object of type Y. There is a lot of myth and bad advice on the web surrounding how to do some of these things.

The "site" in all of the following refer to the IUnknown you are given by Internet Explorer when it calls your IObjectWithSite::SetSite() method.

IWebBrowser2 from site

1. QueryInterface() your site for IID_IServiceProvider.
2. QueryService() the IServiceProvider for SID_STopLevelBrowser, IID_IServiceProvider.
3. QueryService() the top level IServiceProvider for SID_SWebBrowserApp, IID_IWebBrowser2.

IHTMLDocument2 from IWebBrowser2

1. Call IWebBrowser2::get_Document().
2. QueryInterface() the resulting IDispatch pointer for IID_IHTMLDocument2.

IHTMLDocument2 from site

1. Follow steps for "IWebBrowser2 from site" above.
2. Follow steps for "IHTMLDocument2 from IWebBrowser2" above.

IWebBrowser2 from IHTMLDocument2

1. QueryInterface() the IHTMLDocument2 for IID_IServiceProvider.
2. QueryService() the IServiceProvider for SID_SWebBrowserApp, IID_IWebBrowser2.

IHTMLDocument2 from IHTMLElement

1. Call IHTMLElement::get_Document();
2. QueryInterface() the resulting IDispatch pointer for IID_IHTMLDocument2.

IHTMLDocument2 from HWND

1. Use the accessibility hack described at here.

Monday, June 2, 2008

the freedom to choose includes the freedom to choose poorly

No, I am not going to talk about democrotics and our current and upcoming elected officials. I am going to talk about the consumer computer eco-system.

When I was doing IT consulting work during collage, there were a few major players in the PC world: Dell, HP, Compaq and Gateway. They all had their ups and downs with their products. Usually one would be good while the other was making boxes with problems, but then it would switch. Our job was to keep up on who was making good boxes at the time and sell them to our customers. However, we all knew the best machines were machines you built yourself. And we enjoyed building them. So when friends and family would ask me what computer they should buy, I would mention who I though was making a good model, but I would also offer to build them one that was better for cheaper.

When I worked at MSFT, we all had Dell workstations. I would say about 90% of all Windows development took place on Dell machines with Intel Processors. So when friends and family would ask for a computer recommendation, I would point them at Dell. Of course, I no longer had time to build them a machine, though I still built my own from scratch.

Now that I work on PicLens, I have to write code that supports Firefox, Internet Explorer and Safari on both Mac and Windows. We have subsystems that run on top of OpenGL, DirectX, and a software rendered that works in two different modes, depending on which we detect would give better support on a specific system.

Yet we still get a fair number of people who send in e-mail with reports of graphics issues. Some are minor glitches, some are major glitches that make the product unusable. A very small number are blue screens. We take all customer feedback seriously and follow up with them asking about their configuration, etc. Almost all of them have one thing in common: non-premium graphics cards, by which I mean a card that is not a high end ATI or NVidia card.

I am coming to the part where I get to the point.

These days, when friends and family ask me what computer they should get, I think I will start telling them to get a Mac.

Let me be clear, I still hate Macs. With a passion. I have to use one at work, and I remain unconverted. But what they do is take away the freedom to choose poorly.

Let me explain:

With a PC, you never know what you are going to get. And even people who build there own machines often make decisions based on price point, not quality. Not to mention people who build their own machines but do not really understand how hardware and software drivers work.

With a Mac, you always get good hardware. They all have Intel processors. They all have NVidia or ATI graphics cards, with drivers that are known to work. Sure, Microsoft can certify drivers, but they can not test them in every possible configuration of PC hardware. But Apple can test every configuration. Because they only have tens of possibilities instead of thousands.

Nothing has really changed since I was in IT consulting. The trade-offs are still the same: build your own, buy an OEM and roll the dice, or pay a bunch more for a Mac that you can only do so much with but at least it will work. All that has changed is my point of view.

As an idealistic youth, I wanted everyone to get the most from their computing experience. I wanted to educate them about the machines and the software. At Microsoft I just wanted them to leave me alone and figure it out for themselves. Now I just can not be bothered by it at all. Macs work. They stop you from shooting yourself in the foot. And hey, if people think it makes them look cool, then even better.

I will still be building my own machines. My house is all Asus all the time. It is amazing, but I have never had any problems with Asus video cards in Asus mother boards. I prefer NVidia (though it is not a logical or rational preference). I only buy Intel Processors(but that is a completely separate discussion) and Seagate hard drives (though I will accept Western Digital and I really wish there was a quality third player).

Everyone else should get a Mac. It makes my life easier in the short term, since I do not have to do any support. Though, I guess if everyone got a Mac I would have to do ALL my development on a Mac. And I would miss Visual Studio and NTSD.

So, I guess the moral of the story is when choosing a video card, choose wisely. Caveat emptor and all that. Or, spend more than $20 on a video card.

See also: Wired: Graphics Chips Gun for Supremacy in Silicon Showdown