Strategies for Transferring User Data Files in your WP7 Apps By Jay E. Kimble The Dev Theologian

Disclaimers About This Talk Prescriptive session – not necessarily instructive (Emphasis is on Strategy) I am growing, too Let’s make this a dialog The first 2 demos work in WP7 (& in 7.1) The final is about Background Transfers (Mango only)

Background For WP7.0, I built an app that relies on data files that are end-user supplied This was not a problem for my WinMo app I used –a personally created lib for DropBox (but there are numerous options available) –IsolatedStorage –A third party library to simplified WebRequests

IsolatedStorage IsolatedStorage is –a special storage area on the phone –for data files created by your app –for data files downloaded by your app For WP7 (and WP7.1) there is no other local storage option available

Demo 1: Getting our feet wet Simple demo to download an image file (& display it) –We’ll use WebClient for this –We’ll store the resulting file in IsolatedStorage

Download Queues A Download Queue let’s a user manage the process of which files are downloading It also let’s them start/stop transfers We need a few objects to do this: –FileItem containing name, uri, progress, etc. –Collection of FileItems to choose from –Collection of FileItems that are queued to download –Downloader Object

Demo2: Download Queue Let’s look at an implementation of this

Background File Transfers (Bg Xfers) Simplifies the mess of managing requests Only really needs a URI You do need to handle Tombstoning so your app can remember what was downloading between sessions API is controlled via a single shares object which you add transfer requests to

Download Queue == BG Xfers Best Practice By building the Download Queue we actually took care of all the recommended UI! –The only things missing from our UI is A settings mechanism for the user to control when a transfer can happen –Can it happen on battery? –Can it happen on a Cell Data Connection

Tombstoning Sidenote Tombstoning is the process where the OS tells your app –it will be shutting down to free up memory –an app must save off it’s state immediately A separate set of events fire when an app is restored from tombstoning With Bg Xfers you need to always save the state of the transfers when the app is shutting down normally or Tombstoning

Demo3: Background Transfers This demo will create a new MangoDownloader which will BG Transfers (we can actually download up to 5 items at a time!)

Bg Xfers Caveats/Notes It does not work with all Cloud Services –It doesn’t work with SugarSync’s public storage HTTP/HTTPS only (no FTP.. yet..) It will work with other HTTP verbs (post) You can pass post variables and some headers via properties in the Transfer Object Different types of connections have size limitations (be aware of this.. You aren’t downloading a 100mb file on a 3g connection!)

Resources BG Xfers –See the docs on MSDN (especially the best practices Fla-wimo-dev.groups.live.com Joe’s wiki –dfwiki.devfish.net Wp7dev.wikispaces.com