All entries for Thursday 28 August 2008

August 28, 2008

David Tucker's 10 common mistakes when building AIR applications

David Tucker recently posted an article on the Adobe Developer Centre citing 10 common mistakes with developing AIR applications and how to avoid them. I thought I’d quickly compare David’s points against my current AIR project, a remote file-system/transfer manager:

1. Making an application platform specific

David primarily refers here to the UI/UX differences between platforms, but I also found it essential because I encountered significant performance differences with some file system operations (icon getters, mostly), which were fixed with the help of the Flex Profiler. At the moment we can’t test it on the Linux Alpha, but hopefully we’ll be able to try that soon.

2. Not including update capability in an application

We included this as soon as the framework became available and it works very well – whenever the application starts it can check for a newer version of itself, and the user has control over whether to update or not.

3. Changing the application ID after an app has been released

Oops – I ran into this early on; changing the application ID means the update framework will break, amongst other things. Changing the name of your application halfway through the project also risks confusion.

4. Not planning for offline support

Our application relies on a live connection to work, but it does use AIR’s network monitoring APIs to check for a valid connection at startup and then continually monitor connection status, and warns the user if connectivity is lost.

5. Not thinking in AIR

I didn’t find this too difficult – some things were relevant and others weren’t. There have often been moments where I’ve discovered a capability and thought “I didn’t know it could do that”; we do use the application storage directory and the user’s temp directory for file transfers though, and the File , FileStream and FileReference classes were the key to making it work.

6. Using custom chrome to create confusing interfaces

We used the standard chrome, but most of the AIR applications I’ve seen that use custom chrome have done so pretty effectively. One of the most powerful aspects of AIR is that you have very fine control over the UI. As a counter to this though, in addition to the native window chrome there are valid use-cases for having access to native system controls, like toolbars, buttons etc. – platform UI differences can make this even more acute, so I’d like the ability to use standard UI elements where appropriate.

7. Not using the seamless install badge

We implemented this early on – having an install badge makes installation a snap for most people and like the update framework it works well – installation of the AIR runtime can be managed automatically and so far the whole thing has worked fine, except when I broke it myself by not updating the right fields in the updater XML file.

8. Not encrypting sensitive data

Not relevant for this application (yet) – we don’t store any information other than the last file-space used, using a standard SharedObject. AIR has an EncryptedLocalStore for this kind of thing though.

9. Not preserving native interaction

As yet we haven’t got a complete set of keyboard interactions in place (e.g. cut, copy and paste) but some are there. The core interaction type is dragging and dropping, and Flex/AIR gives you control over the process by splitting this action into discreet event-driven stages, so providing visual feedback about whether a drag/drop is allowed can be controlled via your own logic. Something I’ve not yet overcome is how to work with internal and external drag handling at the same time – I may be wrong here but so far it looks like the external drag management only knows about drag in/out operations at the application level, not at the component level, so I need to work on how to use the external drag management to allow items to be dragged into components with the same level of control as the internal drag manager.

A more difficult problem is when a standard component doesn’t quite mimic the operation of a native system control – take the Tree for instance, which will close when its DP is refreshed – in situations like these its nearly always possible to closely replicate the native behaviour by extending or over-riding the component default, but there can be some work involved when finding out what to do. At this point I’ll thank Peter Ent and the excellent Flex Examples Blog for their invaluable resources; they saved me a lot of time.

10. Assuming performance doesn’t matter outside of the browser

In this case, the performance issues highlighted when checking across platforms also highlighted the importance of using the Flex Profiler, the net result being a five-fold increase in speed on OSX and smaller but useful increases on Windows, plus reduced memory usage. The original performance on OSX was bad enough to almost make the application unusable, but after identifying and fixing/working around the problems, the application performs similarly in Windows and OSX.

Thanks to David for writing about what to avoid – fortunately most of them we’d already come across and fixed, so that’s good!


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