Dependency Injection

View and Controller are singletons, so you need some way to access the instance of a specific component. Tornado FX supports dependency injection, but you can also lookup components with the find function.
val myController = find(MyController::class)
When you call find, the component corresponding to the given class is looked up in a global component registry. If it did not exist prior to the call, it will be created and inserted into the registry before the function returns.
If you want to declare the controller referance as a field member however, you should use the inject delegate instead. This is a lazy mechanism, so the actual instance will only be created the first time you call a function on the injected resource. Using inject is always prefered, as it allows your components to have circular dependencies.
val myController: MyController by inject()
Third party injection frameworks
TornadoFX makes it easy to inject resources from a third party dependency injection framework, like for example Guice or Spring. All you have to do is implement the very simple DIContainer interface when you start your application. Let's say you have a Guice module configured with a fictive HelloService. Start Guice in the init block of your App class and register the module with TornadoFX:
val guice = Guice.createInjector(MyModule())
​
FX.dicontainer = object : DIContainer {
    override fun <T : Any> getInstance(type: KClass<T>)
        = guice.getInstance(type.java)
}
The DIContainer implementation is configured to delegate lookups to guice.getInstance
To inject the HelloService configured in MyModule, use the di delegate instead of the inject delegate:
val MyView : View() {
    val helloService: HelloService by di()
}
The di delegate accepts any bean type, while inject will only allow beans of type ScopedInstance, which includes TornadoFX's View and Controller. This keeps a clean separation between your UI beans and any beans configured in the external dependency injection framework.
Setting up for Spring
Above the setup for Guice is shown. Setting up for Spring, in this case using beans.xml as ApplicationContext is done as follows:
beans.xml
<?xml version = "1.0" encoding = "UTF-8"?>
​
<beans xmlns = "http://www.springframework.org/schema/beans"
       xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context = "http://www.springframework.org/schema/context"
       xsi:schemaLocation = "http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
   http://www.springframework.org/schema/context
   http://www.springframework.org/schema/context/spring-context-3.0.xsd">
​
    <context:component-scan base-package="no.tornadofx.fxsample.springexample"/>
    <context:annotation-config/>
</beans>
This sets Spring up to scan for beans.
Application startup
class SpringExampleApp : App(SpringExampleView::class) {
    init {
        val springContext = ClassPathXmlApplicationContext("beans.xml")
        FX.dicontainer = object : DIContainer {
            override fun <T : Any> getInstance(type: KClass<T>): T = springContext.getBean(type.java)
        }
    }
}
This initialized the spring context and hooks it into tornadoFX via the FX.dicontainer. Now you can inject Spring beans like this:
val helloBean : HelloBean by di()
It is quite common in the Spring world to name a bean like so:
<bean id = "helloWorld" class = "com.tutorialspoint.HelloWorld">
     <property name = "message" value = "Hello World!"/>
</bean>
The bean is then accessible using the id. This can be done in tornadoFX too:
class SpringExampleApp : App(SpringExampleView::class) {
    init {
        val springContext = ClassPathXmlApplicationContext("beans.xml")
        FX.dicontainer = object : DIContainer {
            override fun <T : Any> getInstance(type: KClass<T>): T = springContext.getBean(type.java)
	        override fun <T : Any> getInstance(type: KClass<T>, name: String): T = springContext.getBean(type.java,name)
        }
    }
}
The second getInstance uses both the type of the bean and the id of the bean. Instantiating a bean is down as:
val helloBean : HelloBean by di("helloWorld")
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