Scopes

What are Scopes in mvvmFX?

Scopes are data-contexts which can be shared between multiple ViewModels. They reduce the complexity when you have to share information between ViewModels.

Types of Scopes

There are two types of Scopes:

• Global scopes which are Singletons, which can be used with the @InjectViewModel Annotation
• Scopes that are related to an ID

public class PersonMasterViewModel implements ViewModel {

	//Global Instance of the scope will be injected 
	//-> it doesn't matter in which ViewModel you do this -> you'll get the same instance	
	@InjectScope
	private TestScope scope1;

	private TestScope scope2;
	private TestScope scope3;

	PersonMasterViewModel(){
		//get a scope for this ID. If it already exists in the storage you get it,
		//if not, it get's created, stored in the storage and the `Scope` gets returned
		scope2 = ScopeStorage.get(TestScope.class, "myId1");
		scope3 = ScopeStorage.get(TestScope.class, "myId2");
}

#Examples

A good example are Master/Detail Views where you have ViewModels for Master and Detail. In this case you have to transport the information of the current selection from the Master-ViewModel to the Detail-ViewModel.

public class PersonMasterDetailScope implements Scope {
	public ObjectProperty<Person> displayedPerson = new SimpleObjectProperty<>();
	//Some logic which sets the displayed person - for example when the user chooses an element in the master list
	...
}

public class PersonMasterViewModel implements ViewModel {
	
	@InjectScope
	private TestScope scope;

	ObjectProperty<Person> selectedPerson = new SimpleObjectProperty<>();

	public ScopedViewModelA() {
		...
		scope.displayedPerson.bind(selectedPerson);
		...
	}	
}

public class PersonDetailViewModel implements ViewModel {
	
	@InjectScope
	private TestScope scope;

	public ScopedViewModelB() {      
		scope.displayedPerson.addListener((b,o,newSelectedPerson)->initViewModelWithPerson(newSelectedPerson));
	}	
}