Things I wish I learned about Live Tiles a little earlier

I haven't written about .NET here in a while (and probably won't again for another while), but I wanted to put some thoughts up here in case other folks are looking for some details about Live Tiles on the Windows Phone 7.

These are things I learned before and during developing my Gold Price app, which is now available on the Zune marketplace. As well as looking up the current gold price on Yahoo, it puts the price on a Live Tile so you don't even have to open the app to stay current with the price of gold. Feel free to buy it!

Live Tiles are currently one of the unique features of Windows Phones. I love it that my Gold Price app isn't even possible on an iPhone. iOS just doesn't have the notion of 'live' icons on the start screen, beyond a simple (1-100) count. If you're Apple, you can do some fancy icon stuff (like the calendar app, which changes the icon to reflect the day and month), but if you're just a regular iOS developer you're out of luck.

Here are some things I wish I learned about Live tiles a little earlier:

• You can't have an animated Live Tile, unless you're Microsoft. In some ways this is a shame - I dislike restrictions on what developers can do when the OS creator just gets to do whatever the hell they like (such as background processing on both WP7 and iOS). On the other hand, I don't really want the weird and wacky world of Geocities-like animated tiles on my phone either. If there was an option to turn off animated tiles, I'd probably have them turned off anyway, so on balance I won't be losing too much sleep over this one.
• The Live Tile image is (generally) created and hosted on a web server somewhere, not via a callback into your app code. This means there's a dependency on network connectivity for updating the Live Tile.
• This network dependency also means apps that use Live Tiles need to have a server infrastructure behind them, even if it is only a small one. The ongoing cost of a web server means I think we’ll see fewer free Live Tile apps than if there was a server-less way of updating Live Tiles.
• Mike Ormond has a great outline of how to plug a ShellTileSchedule into your app.
• Problems with Live Tile updates are hard to debug. Everything must be just right for it to succeed, but many things can go wrong and I haven't found any way to tell where the problem is.
• Your server must send the Live Tile image within 15 seconds of the request from the phone. This could be a problem if you're dependent on a web service call to another web server (like mine, which currently goes to Yahoo to fetch the pricing data). Network problems, latency, slow servers and bad DNS may be outside your control, but they can all make your image-fetching time lower than you’d like.
• The image itself must be small (less than 80kb in size) It surprised me that the PNG generated for my Live Tile was so big when it's a compressed (albeit lossless) format. I ended up going with JPEG - it looks a little more washed out than the PNG version, but I'm confident it'll have no size issues.
• It surprised me even more that the exact same .NET 4.0 code generated a much larger image file on my server than on my development machine. I ended up putting some code in the image generator/handler to check the size of the generated image (just so I could return an 'error' image that is guaranteed to be small enough) to help track down problems with fetching Live Tiles.
• From discussions with other folks, it looks like the LiveTileSchedule adds the Live Tile update to the schedule, or resets the schedule for that tile if it has stalled because of an error, but - importantly - it doesn't change the time the update is scheduled to run.
  For example, if your Live Tile is scheduled to update in 5 minutes, and you load your app and it calls its LiveTileSchedule code, your Live Tile is still scheduled to run in 5 minutes. (Otherwise someone who opened your app every half hour would constantly reset any hourly schedule and the Live Tile would never update.)
• It is possible to have your app trigger an immediate update of the Live Tile although the code (and the mechanism itself) seems horribly contorted. Mark Monster has a great description of how this all works. You have to set up a Push Notification channel, then have your app send itself a Push Notification telling itself that the Live Tile has been updated. Again, there's a dependency on network connectivity for this to succeed, so even if your app has all the data to generate the new Live Tile itself, and you embed the image generation code in your app, you still need a network available to send a Push Notification from your app to your app using a Live Tile URL local to your app.

If you’ve any comments, or if I’ve got any of this wrong, or if you’ve got a great example of a Live Tile app, please let me know or comment below!