ActionScript Developer's Guide to Robotlegs by Hooks, Joel -- Read -- Imperial Library of Trantor

Index

ActionScript Developer’s Guide to Robotlegs A Note Regarding Supplemental Files Preface

Robotlegs: Something a little bit special Who this book is for Who this book is not for Conventions used in this book Using code examples Safari® Books Online How to contact us Acknowledgments

1. Robotlegs is a lightweight framework for ActionScript 3

What does Robotlegs actually do?

Robotlegs is a communication-and-cooperation framework

Direct conversation Passing messages Robotlegs helps with direct conversations and message passing

Robotlegs makes use of three object-oriented architectural patterns

Do you need a framework at all?

Reasons to use a framework

Consistency Common understanding brings easier collaboration Peer-reviewed solutions A well-tested skeleton Less code to write

Reasons not to use a framework

Framework learning curve Terminology confusion Performance tradeoffs Framework coupling ‘Black box’ code is hard to debug

Robotlegs aims to amp up the pros and minimize the cons

Less boilerplate code is a good thing...

2. The Robotlegs dream...

80% of the problems can be solved with 20% of the API Coding for Robotlegs shouldn’t tie you to the framework Robotlegs aims to enable and not dictate Most AS3 applications benefit from the MVCS approach Testing, 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 Kanban Lindz’s Mosaic Design Tool How a Robotlegs application gets things done

Architecture begins with Events and Commands

Getting to grips with Robotlegs architecture

The ‘context’ is the heart of your Robotlegs application Your models and services are ‘Actors’ in your app The MediatorMap provides a way to join your views to your app layer Robotlegs mediators are bridges, not view controllers The CommandMap makes things happen The shared event dispatcher joins everything together

... and it goes a little something like this (event flow)

User stories as implemented in Robotlegs

Personal Kanban example: Moving a task from ‘backlog’ to ‘doing’ Mosaic Design Tool example: Saving a design The same but different

All 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 object You can fulfil a dependency in three different ways

You already use Dependency Injection There are different ways to inject dependencies

Statics and globals make code rigid, brittle, hard to test, and prone to memory leaks Locator patterns push extra responsibilities on your classes

Automated DI gets around the need to ‘pass the parcel’, but keeps code flexible How does Robotlegs Injection work?

Automated DI is a handshake

You can specify an injection point in three ways And you also have to tell the injector what you would like it to do

Robotlegs has different types of injection

If you only want one instance, use mapSingleton mapSingletonOf keeps your code coupled only to interfaces What 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 metadata

FlashBuilder/FlexBuilder solution Flash CS4/CS5 IDE Solution IntelliJ Solution Flex SDK Solution—command line compiling Flex SDK Solution—compiling with ant

Automated 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 type If 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-view Ask it to run startup()—immediately or when you’re ready Use startup() to provide your injection rules, map your mediators to views and commands to events Shutting down a Context Now you have some Context

6. The CommandMap in action

A Command is a concise single-purpose controller object Commands are triggered by events Commands can be any class with an ‘execute’ method Commands should do their thing and then die Commands rely on their injections to be useful

You can inject the event that triggered the command

Commands know about the injector, command map, mediator map and context view Commands can also dispatch events Great command names pay dividends Use helper classes for shared logic Detain and release when you need your command to hang around

7. Models and services: How are they different?

Models and Services usually extend Actor They don’t listen, they only talk Use your API through a Command Distinguishing Models from Services Classes that don’t dispatch events to the shared event dispatcher don’t need to extend Actor Configuring services

Configuring services using a command Configuring services by injecting the configuration

Working with non-Actor models and services (including third party code)

Wrap them in an Actor Use the command that acts upon them to dispatch the events

Model design tips for Robotlegs

Keep those responsibilities separated Use strong-typed wrappers for collections Never create mutually dependent models

Managing the relationships between models and services

8. Connecting views with Mediators

Introducing the MediatorMap

Wiring views with the MediatorMap

Mediating your view components

Mediators are created when your view hits the stage Mediator Structure Avoid logic in your Mediators Do your wiring in onRegister() Using the EventMap

Use the ‘eventClass’ parameter to make mappings that are type safe

You can do manual clean-up in onRemove

Why can’t Mediators be injected into other objects? Working with complex composite views Using the same mediator with more than one view A good Mediator is just a mailman

Signs that you need another mediator Never put view logic into the mediator.

9. Working with Robotlegs: Rich Examples

Feature implementation walk-through: Mosaic Tool

Challenge 1: Keeping things on a need-to-know basis Challenge 2: Keeping the view snappy Keeping the models in line with the visual design

The crucial Robotlegs mappings that tie it all together The tile color update again, but this time with code

Feature implementation walk-through: Personal Kanban App

How new tasks are entered

The crucial Robotlegs mappings that make this sequence work Adding a new task again, but this time with code

Wait, I want more examples!

10. Testing your Robotlegs application

Your test provides the injections Testing models Testing services Testing commands Testing mediators

Testing that an event dispatched by the view results in the correct event being dispatched on the shared event dispatcher Testing that an event received on the shared event dispatcher results in an action on the view

11. Power-ups

Bootstraps can break up fat contexts The ContextEvents help keep control Tag methods with [PostConstruct] to run them after injection is complete Use Signals between complex views and their mediators Modular and multiple-context Robotlegs

ModuleEventDispatcher and child injectors make it work

Extend Robotlegs with utilities and add-ons ViewMap—injection for your views Mediator map performance

A. Troubleshooting tips

Problem: Injection doesn’t occur

Broken injection point declaration Metadata is being stripped by the compiler Instantiating an object with injected dependencies using new Injected properties are null in constructor

Problem: Things work for a while and then mysteriously stop Problem: Event dispatch does not work as expected Problem: Mediator isn’t running onRegister

Make mediator mappings from the inside out

Problem: Handlers in the mediator are running repeatedly Error: Injector missing rule for X

Missing injection mapping Inconsistent injection mapping

Warning: Duplicate mapping in the injector Error: Call to a possibly undefined method X Where 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 Colophon Copyright

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