Contributed by Josh McDonald
SmartyPants-IOC is a dependency injection framework for use in building Adobe Flex and Flash applications inspired by Google Guice for Java. It's based on key concepts:
The class+name key
Injector requests, usually specified via metadata
Injector rules, specified using an ActionScript-based DSL
Whether you're telling SmartyPants-IOC what to provide or sitting around with your hand out asking for a dependency, the key is the same: a combination of a class and a name. You must specify the class, but the name is optional.
How do you actually request that a field be injected? In most circumstances you need to annotate your fields with ActionScript metadata. If you want to request an instance of IServiceInterface, the syntax is simple:
[Inject] public var myService:IServiceInterface;
Let's say you want to look up a particular string, rather than just anything. For a Web Services Description Language (WSDL) URL, or something along those lines, use this syntax:
[Inject(name="mainWSDL")] public var myServiceWSDL:String;
These fields will be injected into your object when it's constructed for you by SmartyPants-IOC or when you call injector.injectInto(myInstance).
SmartyPants-IOC also supports live injections, which when coupled with live rules behave like the Flex SDK's data-binding functionality:
//This will be set whenever the source changes [Inject(name="userName",live)] public var currentUsername:String;
The injector rules are akin to Guice's bindings, but we use another term to avoid confusion with the Flex SDK's data-binding mechanism. You tell the injector what you'd like it to do, using the DSL. Here are a couple of examples:
//Simple singleton rules:
injector.newRule().whenAskedFor(String).named("wsdl")
.useInstance("http://www.server.com/soap/service.wsdl");
injector.newRule().whenAskedFor(IServiceInterface)
.useSingletonOf(MyServiceImpl);
injector.newRule().whenAskedFor(MyConcreteClass).useSingleton();
//"Live" rules act just like <mx:Binding>
injector.newRule().whenAskedFor(String)
.named("userId")
.useBindableProperty(this, "userId");Good question! Two ways. First, in an MXML component, this code will inject into your component on the CreationComplete event:
<?xml version="1.0" encoding="utf-8"?>
<mx:Canvas xmlns:mx="http://www.adobe.com/2006/mxml"
xmlns:smartypants="http://smartypants.expantra.net/2008">
<smartypants:RequestInjection/>
<!-- ...Regular code and MXML... -->
</mx:Canvas>And in ActionScript it's even simpler:
SmartyPants.injectInto(this);
Hopefully this gives a little more insight into the style and ideas behind SmartyPants-IOC. Be sure to check it out on the Google Code site!
SmartyPants-IOC is hosted on Google Code: http://code.google.com/p/smartypants-ioc/.