= ViewModel
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Indicates that an object belongs to the UI/application layer and is intended to be used as a view-model.Naturally this also allows for the idiom of passing in the xref:refguide:applib:index/services/inject/ServiceInjector.adoc[ServiceInjector] as an argument and programmatically resolve any field-style injection points via _ServiceInjector#injectServicesInto(Object)_ , that is, if already required during _construction_ .

Instances of xref:refguide:applib:index/ViewModel.adoc[ViewModel] must include (at least) one public constructor.

Contract:

* there is either exactly one public constructor or if there are more than one, then only one of these is annotated with any of _@Inject_ or _@Autowired(required=true)_ (meta-annotations are also considered)
* the constructor may have arbitrary many arguments of arbitrary type
* first _String_ argument found is passed in the view-model's memento
* any other arguments are resolved via the xref:refguide:applib:index/services/registry/ServiceRegistry.adoc[ServiceRegistry] - if no _Bean_ can be found a _NoSuchElementException_ is thrown
* there is no support for _Spring_ programming model specific annotations on constructor arguments (perhaps future work)

After a view-model got new-ed up by the framework (or programmatically via the xref:refguide:applib:index/services/factory/FactoryService.adoc[FactoryService] ), _ServiceInjector#injectServicesInto(Object)_ is called on the viewmodel instance, regardless of what happened during _construction_ .

== API

[source,java]
.ViewModel.java
----
interface ViewModel {
  String viewModelMemento()     // <.>
}
----

<.> xref:#viewModelMemento_[viewModelMemento()]
+
--
Obtain a memento of the view-model. (Optional)
--

== Members

[#viewModelMemento_]
=== viewModelMemento()

Obtain a memento of the view-model. (Optional)

Captures the state of this view-model as _String_ , which can be passed in to this view-model's constructor for later re-construction.

The framework automatically takes care of non-URL-safe strings, null and the empty String. Those view-model mementos are also digitally signed, before the are handed out to clients.
