table page 4 - Dave's Blog

Notes on Creating Internet Explorer Extensions in C++ and COM

Working on Internet Explorer extensions in C++ & COM, I had to relearn or rediscover how to do several totally basic and important things. To save myself and possibly others trouble in the future, here's some pertinent links and tips.

First you must choose your IE extensibility point. Here's a very short list of the few I've used:

• Explorer Bars and IE Toolbars
• IE Tools, IE Help, and IE Context Menu menu items
• IE Toolbar Buttons

Once you've created your COM object that implements IObjectWithSite and whatever other interfaces your extensibility point requires as described in the above links you'll see your SetSite method get called by IE. You might want to know how to get the top level browser object from the IUnknown site object passed in via that method.

After that you may also want to listen for some events from the browser. To do this you'll need to:

1. Implement the dispinterface that has the event you want. For instance DWebBrowserEvents2, or HTMLDocumentEvents, or HTMLWindowEvents2. You'll have to search around in that area of the documentation to find the event you're looking for.
2. Register for events using AtlAdvise. The object you need to subscribe to depends on the events you want. For example, DWebBrowserEvents2 come from the webbrowser object, HTMLDocumentEvents come from the document object assuming its an HTML document (I obtained via get_Document method on the webbrowser), and HTMLWindowEvents2 come from the window object (which oddly I obtained via calling the get_script method on the document object). Note that depending on when your SetSite method is called the document may not exist yet. For my extension I signed up for browser events immediately and then listened for events like NavigateComplete before signing up for document and window events.
3. Implement IDispatch. The Invoke method will get called with event notifications from the dispinterfaces you sign up for in AtlAdvise. Implementing Invoke manually is a slight pain as all the parameters come in as VARIANTs and are in reverse order. There's some ATL macros that may make this easier but I didn't bother.
4. Call AtlUnadvise at some point -- at the latest when SetSite is called again and your site object changes.

If you want to check if an IHTMLElement is not visible on screen due how the page is scrolled, try comparing the Body or Document Element's client height and width, which appears to be the dimensions of the visible document area, to the element's bounding client rect which appears to be its position relative to the upper left corner of the visible document area. I've found this to be working for me so far, but I'm not positive that frames, iframes, zooming, editable document areas, etc won't mess this up.

Be sure to use pointers you get from the IWebBrowser/IHTMLDocument/etc. only on the thread on which you obtained the pointer or correctly marshal the pointers to other threads to avoid weird crashes and hangs.

Obtaining the HTML document of a subframe is slightly more complicated then you might hope. On the other hand this might be resolved by the new to IE8 method IHTMLFrameElement3::get_contentDocument

Check out Eric's IE blog post on IE extensibility which has some great links on this topic as well.

The 'Is It UTF-8?' Quick and Dirty Test

I've found while debugging networking in IE its often useful to quickly tell if a string is encoded in UTF-8. You can check for the Byte Order Mark (EF BB BF in UTF-8) but, I rarely see the BOM on UTF-8 strings. Instead I apply a quick and dirty UTF-8 test that takes advantage of the well-formed UTF-8 restrictions.

Unlike other multibyte character encoding forms (see Windows supported character sets or IANA's list of character sets), for example Big5, where sticking together any two bytes is more likely than not to give a valid byte sequence, UTF-8 is more restrictive. And unlike other multibyte character encodings, UTF-8 bytes may be taken out of context and one can still know that its a single byte character, the starting byte of a three byte sequence, etc.

The full rules for well-formed UTF-8 are a little too complicated for me to commit to memory. Instead I've got my own simpler (this is the quick part) set of rules that will be mostly correct (this is the dirty part). For as many bytes in the string as you care to examine, check the most significant digit of the byte:

F:

This is byte 1 of a 4 byte encoded codepoint and must be followed by 3 trail bytes.

E:

This is byte 1 of a 3 byte encoded codepoint and must be followed by 2 trail bytes.

C..D:

This is byte 1 of a 2 byte encoded codepoint and must be followed by 1 trail byte.

8..B:

This is a trail byte.

0..7:

This is a single byte encoded codepoint.

DIY Pepsi Challenge

Microsoft isn't completely shielded from our economies issues but I still have a job and still get free soda. While that's all still the case, I decided to test Sarah's claimed ability to differentiate between Pepsi, Coke, and their diet counterparts by taste alone. I poured the four sodas into marked cups and Sarah and I each took two runs through the cups with the following guesses.

As you can see from the results, Sarah's claimed ability to identify Coke and Pepsi by taste is confirmed. The first run through she got completely correct and on the second run only mistook Diet Pepsi for Diet Coke. Her excuse for the error on the second run was a tainted palate from the first run. I on the other hand was mostly incorrect. Surprisingly though my incorrect answers were mostly consistent between run one and two. For instance I thought Pepsi was Coke in both runs.

Back from California

Sarah and I are back from a short Christmas visit to California. We spent the days around Christmas with much of my extended family in Sacramento many of whom I had not seen in quite a while. It was nice to see everybody again. I ended up taking a few pictures on Christmas in order to add to the digital photo frame I gave Grandma.

We flew in and out of San Francisco on Virgin America which was really nice. The staff is trying their best to be hip but accessible, the safety instructional video is entertaining, there's mood lighting, and all seats have entertainment systems as well as power outlets and USB ports to charge your electronic devices. They don't have many flights which appears to mean shorter lines. And it was cheaper to fly with them and then rent a car and drive to Sacramento then to fly in to Sacramento. I'll for sure be flying with them again given the opportunity. Before flying back Sarah and I spent a day in San Francisco, where we decided that if we don't go back to Fisherman's Wharf again in this lifetime that would be acceptable, saw the Golden Gate Park and met up with my friend Jake who I haven't seen in at least four years. Next up, happy new year!

Marienplatz and the Deutsches Museum

On Monday in Germany we went to Marienplatz and wandered around the Christmas Market, some of the stores, had drinks in a little pub, visited the Toy Museum, and checked out an impressive looking church. We accidentally drew in some other tourists as we stood gaping at the Glockenspiel tower waiting for the little show to begin at the wrong hour. That night Megan and Oliver came by our hotel and took us out to a traditional Bavarian restaurant and brewery that had been brewing beer there for hundreds of years. It was fun although we may have kept Megan and Oliver out too late on a weeknight.

The next day we went to the Deutsches Museum the largest science and technology museum in the world. And indeed it is very large, six floors on a large grounds. I needed to better pace myself: I spent too much energy being interested in the engineering sections with steam engines, mining, aerospace etc. I was completely worn out by the time we got to physics, chemistry, etc. etc. and we didn't even look in the natural sciences section. Anyway, its very large. That night we ate with Jon at an Italian restaurant. During the meal two period dressed children came in and began singing then tried to shake down their captive audience in the restaurant asking for money. The man at the table next to us asked one of the children what charity the money was going towards, the child said they kept the money, and the man said never mind then and sent the child away.

I Voted

This past Tuesday I voted in my first presidential election. Of course I was eligible twice before so don't tell my social studies teacher. I read about folks who stood in line for twelve hours waiting to vote but I personally had no issues. I found the voting location around 10am and it seemed appropriately busy: There were people voting but no lines. I came in and looked confused until an elderly lady gave me a paper to bubble in. The voting booth was more like a fold out voting table at a very awkward height and in the end my back ached. It feels better to vote in person and have a back ache after. Its more like I've accomplished something.

Investigation of a Few Application Protocols (Updated)

Windows allows for application protocols in which, through the registry, you specify a URL scheme and a command line to have that URL passed to your application. Its an easy way to hook a webbrowser up to your application. Anyone can read the doc above and then walk through the registry and pick out the application protocols but just from that info you can't tell what the application expects these URLs to look like. I did a bit of research on some of the application protocols I've seen which is listed below. Good places to look for information on URI schemes: Wikipedia URI scheme, and ESW Wiki UriSchemes.

Cadbury Bunny Sneaks Mint

	Cadbury Bunny Sneaks Mint Cadbury the bunny takes a moment from hiding under the chair to eat some mint. She comes out just to grab some mint and then goes back under the chair repeatedly for two minutes.	From: David Risney Views: 328 1 ratings
	Time: 02:01	More in Pets & Animals