#Introduction to Smartypants rules

Introduction

The Smartypants IOC system uses injector rules when deciding how to fulfil a request.

Details

Each rule essentially matches a key to an instance (either an implementation, or a provider, or another rule). A key consists of a Class (or interface) and an optional name. An example would be (IUIComponent named "BlueButton").

Adding a new rule is easy:

Class Binding

//Get our injector
injector = SmartyPants.getOrCreateInjectorFor(this);
//Add some rules
injector.newRule().whenAskedFor(IUIComponent).named("BlueButton").useClass(Button);
injector.newRule().whenAskedFor(IUIComponent).useClass(Canvas);

This example demonstrates simple class binding, with the following meanings:

• When injecting a IUIComponent named "BlueButton", provide an instance of Button.
• When injecting an unnamed IUIComponent, provide an instance of Canvas.

Instance Binding (singletons)

injector.newRule().whenAskedFor(String).named("wsdl").useInstance("http://www.server.com/soap/service.wsdl");
injector.newRule().whenAskedFor(IService).useSingletonOf(com.company.ServiceImpl);

In this example, we're binding:

• The instance "http://www.server.com/soap/service.wsdl" to any requests for a String named "wsdl".
• A "lazy singleton" of class ServiceImpl to any requests for an IService.

Lazy singletons (useSingletonOf) are not created until they're needed, whereas useInstance binds to an existing instance.

Provider Binding

injector.newRule().whenAskedFor(Button).useProvider(myProviderInstance);

Binds to an instance of a class that implements to Provider interface.

Rule Binding

injector.newRule().whenAskedFor(IUIComponent).named("RedButton").useRuleFor(IUIComponent, "BlueButton");

This code redirects all requests for (IUIComponent named "RedButton") to whatever is bound to (IUIComponent named "BlueButton")

Live rules

Live rules in Smartypants are the IOC equivalent to the Flex SDK's data-binding functionality. For example:

[Bindable]
public var companyList : ArrayCollection;

injector.newRule().whenAskedFor(ArrayCollection).named("allCompanies").useBindableProperty(this, "companyList");

This, combined with live injection (see the request documentation) allows you to make use Flex databinding between model and view classes without any direct coupling between them.