Adventures in Facebook®: Lessons Learned from a Landmark webOS App

Adventures in Facebook®:Lessons Learned from a Landmark webOS App
Kevin Decker
Developer Relations Engineer
April 24, 2010

Best Practices
Debugging
Tools
Classes and Libraries
Open Source
Agenda

Best Practices

Widgets
Problem
Duplicated UI and backing logic throughout the app
Maintenance nightmare
Solution
Custom Mojo™ widgets

Widgets
Class in Mojo.Widget namespace
setup function
Renders HTML
Registers events
cleanup function
Unregisters events, etc.
All Mojo APIs available
Reference class by name in x-mojo-element attribute

Widgets—Advanced
Subwidgets
controller.instantiateChildWidgets(controller.element)
controller.exposeMethod
Mojo.Event.send

Avoid Document References
Multiple stage = multiple documents
Execution occurs in data document
Consequences:
References to document object will fail
document.getElementById
document.querySelector
Mojo.Controller.stageController
Prototype extensions may fail
Multiple stage readiness

Avoid Document References
Fixes:
document.getElementById
sceneController.get
document.querySelector
sceneController.sceneElement.querySelector
Mojo.Controller.stageController
sceneController.stageController
Mojo.appController.getActiveStageController
$(elId).x()
Form/Element.x(sceneController.get(elId))
Multiple stage readiness

Periodic Tasks
Two methods:
palm://com.palm.power/timeout service
setInterval
Limited to app lifetime: setInterval
Outliving app: Timeout service

Debugging

Inspecting Multistage Applications
Process/document under Multistage
Data document
Stage documents
applicationManager service
bit.ly/aQFnuF
stage-inspect script
github.com/kpdecker/stage-inspect

Logging
Error.prototype.toString
Function wrappers
wrapInLogger
wrapInErrorHandler
DebugLogging.wrapInErrorHandler(
"Mojo.Controller.SceneController”,
[ "assistantSetup", "assistantCleanup" ]);
traceWrapper
Exceptions are not logged in API callbacks
DEBUGGING ONLY

Tools
palm-run
Build+execution utility
Build
Deploy
Launch
Log
github.com/dalmaer/palm-run
i18nScanner
Scans for untranslated JavaScript and HTML strings
Generates report of i18n tokens
github.com/kpdecker/i18nScanner

Classes and Libraries

Operation Queue
Frequently need to block multiple calls on a method
Init callbacks
Dataset refresh
OperationQueue
queue
getSuccessHandler
getErrorHandler
Login
Status
Notify

Observer Manager
Alternative to sendEventToCommanders and sendToNotificationChain APIs
Notifications while scene/stage inactive
Deferred notifications
ObserveManager
setup
cleanup
observe
stopObserving

Service Request Wrapper
Mojo.Service.Request maintain weak reference
Garbage collection can prevent callback
ServiceRequestWrapper
request
Same signature as Mojo.Service.Request
Maintains references
Cancels completed requests
Similar to scene serviceRequest

Caching Data
Remote data sources
Potentially broken connections
User expectations
CacheManager
Depot wrapper
Simplifies init, access, and expiration
load
store

Paging Data Source
Many data sources only differ in a few places
Examples
Event List
Profile Wall
Common needs:
Paging
Arbitrary size
Caching
DataModelBase
getRange
Look ahead algorithm
refresh
Subclasses:
loadRange
getCacheName

Continuously Loading Paged List
UI companion to paged data list
Transparently handles page loading
Refresh indicator
Mojo.Widget.PagedList
<div id=“listName” x-mojo-element=“PagedList”></div>
this.controller.setupWidget("listEvents", {
itemTemplate: "events-list/events-item-template”,
emptyTemplate: "events-list/events-empty-template”,
hasNoWidgets: true
}, this.eventList);

Open Sourced
All of the libraries open sourced
github.com/palm/webos-samples
Further details (to come)
incaseofstairs.com

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Adventures in Facebook®: Lessons Learned from a Landmark webOS App

by Kevin Decker on Apr 27, 2010

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