Difference between revisions of "Data Persistence"

Revision as of 05:59, 17 March 2008

UNDER CONSTRUCTION --Wayn3w 05:59, 17 March 2008 (PDT)

Sometimes widgets take information from users that should be stored for later. For instance, if a user changes the color of a screen by pressing on it, then when the widget next loads it should still use this color.

Persisting to Chumby Servers: the Chumby API

• persists across Chumby reboots
• may take longer because of network fetches

Persisting Locally: Mobile Shared Objects

This involves using objects of the SharedObject class. An excellent tutorial for the using them is Persistent data: Saving user preferences and game scores. Things to note about them are:

• they are stored in /tmp/pdata, but it is not easily readable
• they will be removed when a Chumby restarts.
• flashplayer does not support shared objects, so this will have to be tested on the Chumby.

General Approach

• since it uses a callback, rather than listener pattern, the handler will not have the context of the instance. hence if the callback needs to invoke a method on an instance, then it will have to refer to a reference to the instance that is stored globally.

MTASC Issues

MTASC has an older, incomplete definition for SharedObject. The file SharedObject.as (on Linux stored in /usr/share/mtasc/std/SharedObject.as) will have to be edited to include the following code:

static function addListener(objectName:String, notifyFunction:Function): Void;
static function removeListener(objectName:String): Void;

With this definition of SharedObject, it is not possible to have private data -- that is, data on the shared object that will not persist. This is not a detriment, because in an object-oriented project there will be other places to store private data. Note that this makes it difficult to derive a new class from SharedObject.

Debugging

trace() is your friend.