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Dice

Lightweight dependency injection framework for Dart.

# Quick Guide

Dice is configured by creating a Module instance that acts as factory binding your classes to instances. Modules are passed to an Injector which looks for @inject annotations and resolves them to instances bound in your module. It's really quite simple:

1. Add the folowing to your pubspec.yaml and run pub install

    dependencies:
      dice: any

2. Create some classes and interfaces to inject

	class BillingServiceImpl implements BillingService {
	  @inject
	  CreditProcessor _processor;
	  
	  Receipt chargeOrder(Order order, CreditCard creditCard) {
	    if(!_processor.validate(creditCard)) {
	      throw new ArgumentError("payment method not accepted");
	    }
	    // :
	  }
	}

3. Register the type/class bindings in a module

	class ExampleModule extends Module {
	  configure() {
	    // bind CreditProcessor to a singleton
	    bind(CreditProcessor).toInstance(new CreditProcessorImpl());
	    // bind BillingService to a prototype
	    bind(BillingService).toType(BillingServiceImpl);
	  }
	}

4. Run it

    import "package:dice/dice.dart";
	main() {
	  	var injector = new Injector(new ExampleModule());
	  	var billingService = injector.getInstance(BillingService);
	  	var creditCard = new CreditCard("VISA");
	  	var order = new Order("Dart: Up and Running");
	  	billingService.chargeOrder(order, creditCard);
	}

for more information see the full example here.

Dependency Injection with Dice

You can use the @inject annotation to mark values for injection the following ways:

  • Injection of public and private fields (object/instance variables)
	class MyOtherClass {
    	@inject
      	SomeClass field;
      	@inject
      	SomeOtherClass _privateField;
   	}
  • Injection of constructor parameters
	class MyClass {
 		@inject
 		MyClass(this.field);
 		
 		MyOtherClass field;
 	}
  • Injection of public and private setters
	class SomeClass {
      	@inject
      	set value(SomeOtherClass val) => _privateValue = val;
      	
      	@inject
      	set _value(SomeOtherClass val) => _anotherPrivateValue = val;

      	SomeOtherClass _privateValue, _anotherPrivateValue;
	}

The actual values injected are configured by extending the Module class and using one its binder functions

  • bind(MyType).toInstace(object) bind type MyType to existing object (singleton injections)
  • bind(MyType).toType(MyType) bind type MyType to an (possible alternative) class implementing it.
  • bind(MyTypedef).toFunction(function) bind a typedef to a function matching it.
  • bind(MyType).toBuilder(() => new MyType()) bind MyType to function that can build instances of it

Named Injections

Dice supports named injections by using the @Named annotation. Currently this annotation works everywhere the @inject annotation works, except for constructors.

	class MyClass {
      	@inject
      	@Named('my-special-implementation')
      	SomeClass _someClass;
   	}

The configuration is as before except you now use method namedBind inside your Module implementation.

  • namedBind(MyType, "my-name").toInstace(object)
  • namedBind(MyType, "my-name").toType(MyType)
  • namedBind(MyTypedef, "my-name").toFunction(function)
  • namedBind(MyType, "my-name").toBuilder(() => new MyType())

Tips and Tricks

Tip 1. Instead of using the @inject annotation to resolve injections you can use the injectors getInstance method

   MyClass instance = injector.getInstance(MyClass);

Tip 2. Instead of using the @Named annotation to resolve named injections you can use the Injector directly

   MyType instance = injector.getNamedInstance(MyType, "my-name");

Tip 3. You can use named bindings to create a simple yet effective way of injecting configuration values into your application.

	class TestModule extends Module {
    	configure() {
			namedBind("web-service-host", String).toInstace("http://test-service.name");
		}
	}
	
	// application code
	String get webServiceHost => injector.getNamedInstance(String, "web-service-host");

Libraries

dice

Lightweight dependency injection framework for Dart.