Strategies for Transferring User Data Files in your WP7 Apps

Strategies for Transferring User Data Files in your WP7 Apps By Jay E. KimbleThe Dev Theologian http://jaykimble.net

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 FileItemsthat are queued to download • Downloader Object

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

Background File Transfers (BgXfers) • 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

TombstoningSidenote • 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 BgXfers 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!)

BgXfers 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

Strategies for Transferring User Data Files in your WP7 Apps