book

ActionScript Developer's Guide to Robotlegs

by Stray, Joel Hooks

August 2011

Intermediate to advanced

136 pages

3h 9m

English

O'Reilly Media, Inc.

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A Note Regarding Supplemental Files
Preface
Robotlegs: Something a little bit specialWho this book is forWho this book is not forConventions used in this bookUsing code examplesSafari® Books OnlineHow to contact usAcknowledgments
1. Robotlegs is a lightweight framework for ActionScript 3
What does Robotlegs actually do?Robotlegs is a communication-and-cooperation frameworkDirect conversationPassing messagesRobotlegs helps with direct conversations and message passingRobotlegs makes use of three object-oriented architectural patternsDo you need a framework at all?Reasons to use a frameworkConsistencyCommon understanding brings easier collaborationPeer-reviewed solutionsA well-tested skeletonLess code to writeReasons not to use a frameworkFramework learning curveTerminology confusionPerformance tradeoffsFramework coupling‘Black box’ code is hard to debugRobotlegs aims to amp up the pros and minimize the consLess boilerplate code is a good thing...
2. The Robotlegs dream...
80% of the problems can be solved with 20% of the APICoding for Robotlegs shouldn’t tie you to the frameworkRobotlegs aims to enable and not dictateMost AS3 applications benefit from the MVCS approachTesting, testing! (We test, and we make it easy for you to test)Some final things every Robotlegs cadet should know
3. Anatomy of a Robotlegs application
Joel’s Personal KanbanLindz’s Mosaic Design ToolHow a Robotlegs application gets things doneArchitecture begins with Events and CommandsGetting to grips with Robotlegs architectureThe ‘context’ is the heart of your Robotlegs applicationYour models and services are ‘Actors’ in your appThe MediatorMap provides a way to join your views to your app layerRobotlegs mediators are bridges, not view controllersThe CommandMap makes things happenThe shared event dispatcher joins everything together... and it goes a little something like this (event flow)User stories as implemented in RobotlegsPersonal Kanban example: Moving a task from ‘backlog’ to ‘doing’Mosaic Design Tool example: Saving a designThe same but differentAll of this is possible because of the Robotlegs Injector
4. Automated Dependency Injection
So, what exactly is Automated Dependency Injection?A dependency is just a requirement to use another objectYou can fulfil a dependency in three different waysYou already use Dependency InjectionThere are different ways to inject dependenciesStatics and globals make code rigid, brittle, hard to test, and prone to memory leaksLocator patterns push extra responsibilities on your classesAutomated DI gets around the need to ‘pass the parcel’, but keeps code flexibleHow does Robotlegs Injection work?Automated DI is a handshakeYou can specify an injection point in three waysAnd you also have to tell the injector what you would like it to doRobotlegs has different types of injectionIf you only want one instance, use mapSingletonmapSingletonOf keeps your code coupled only to interfacesWhat if my class has to be created elsewhere? (e.g. a factory)Named rules let you create multiple rules for each class (but they’re icky)You need to tell the compiler to include the injection metadataFlashBuilder/FlexBuilder solutionFlash CS4/CS5 IDE SolutionIntelliJ SolutionFlex SDK Solution—command line compilingFlex SDK Solution—compiling with antAutomated Injection ‘Gotchas’If an object has an [Inject]ed dependency you have to create it using the Injector.You can map injection rules at runtime, but beware of race conditions.The injection point and rule have to be of exactly the same typeIf you override a method that has an [Inject] tag, you need to add it in the subclass
5. The Robotlegs context in action
Provide the context with a root-viewAsk it to run startup()—immediately or when you’re readyUse startup() to provide your injection rules, map your mediators to views and commands to eventsShutting down a ContextNow you have some Context
6. The CommandMap in action
A Command is a concise single-purpose controller objectCommands are triggered by eventsCommands can be any class with an ‘execute’ methodCommands should do their thing and then dieCommands rely on their injections to be usefulYou can inject the event that triggered the commandCommands know about the injector, command map, mediator map and context viewCommands can also dispatch eventsGreat command names pay dividendsUse helper classes for shared logicDetain and release when you need your command to hang around
7. Models and services: How are they different?
Models and Services usually extend ActorThey don’t listen, they only talkUse your API through a CommandDistinguishing Models from ServicesClasses that don’t dispatch events to the shared event dispatcher don’t need to extend ActorConfiguring servicesConfiguring services using a commandConfiguring services by injecting the configurationWorking with non-Actor models and services (including third party code)Wrap them in an ActorUse the command that acts upon them to dispatch the eventsModel design tips for RobotlegsKeep those responsibilities separatedUse strong-typed wrappers for collectionsNever create mutually dependent modelsManaging the relationships between models and services
8. Connecting views with Mediators
Introducing the MediatorMapWiring views with the MediatorMapMediating your view componentsMediators are created when your view hits the stageMediator StructureAvoid logic in your MediatorsDo your wiring in onRegister()Using the EventMapUse the ‘eventClass’ parameter to make mappings that are type safeYou can do manual clean-up in onRemoveWhy can’t Mediators be injected into other objects?Working with complex composite viewsUsing the same mediator with more than one viewA good Mediator is just a mailmanSigns that you need another mediatorNever put view logic into the mediator.

9. Working with Robotlegs: Rich Examples
Feature implementation walk-through: Mosaic ToolChallenge 1: Keeping things on a need-to-know basisChallenge 2: Keeping the view snappyKeeping the models in line with the visual designThe crucial Robotlegs mappings that tie it all togetherThe tile color update again, but this time with codeFeature implementation walk-through: Personal Kanban AppHow new tasks are enteredThe crucial Robotlegs mappings that make this sequence workAdding a new task again, but this time with codeWait, I want more examples!
10. Testing your Robotlegs application
Your test provides the injectionsTesting modelsTesting servicesTesting commandsTesting mediatorsTesting that an event dispatched by the view results in the correct event being dispatched on the shared event dispatcherTesting that an event received on the shared event dispatcher results in an action on the view
11. Power-ups
Bootstraps can break up fat contextsThe ContextEvents help keep controlTag methods with [PostConstruct] to run them after injection is completeUse Signals between complex views and their mediatorsModular and multiple-context RobotlegsModuleEventDispatcher and child injectors make it workExtend Robotlegs with utilities and add-onsViewMap—injection for your viewsMediator map performance
A. Troubleshooting tips
Problem: Injection doesn’t occurBroken injection point declarationMetadata is being stripped by the compilerInstantiating an object with injected dependencies using newInjected properties are null in constructorProblem: Things work for a while and then mysteriously stopProblem: Event dispatch does not work as expectedProblem: Mediator isn’t running onRegisterMake mediator mappings from the inside outProblem: Handlers in the mediator are running repeatedlyError: Injector missing rule for XMissing injection mappingInconsistent injection mappingWarning: Duplicate mapping in the injectorError: Call to a possibly undefined method XWhere to get more help
B. Swiftsuspenders: The power behind the Robotlegs Injector
What does Swiftsuspenders actually do?We think limited metadata is a good thing
About the Authors
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ActionScript Developer's Guide to Robotlegs

by Stray, Joel Hooks

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