Zones
Zones are the mechanism via which multiple independent ArezContext instances
can co-exist in the same application. Each context is isolated from other other contexts. A consequence of
this is that observable properties and computed properties in one zone can not be accessed from a different
zone. Thus observers will not react to changes from a different zone and actions can only change observable
properties from the same zone.
Zones are an advanced concept and not used in the typical application. Zones can add some runtime overhead
depending on the way that they are used. As a result, developers must explicitly enable zones at compile time.
This is activated by setting the arez.enable_zones configuration property to true in a .gwt.xml module.
When zones are enabled, the Arez.context() method will return the
ArezContext of the current zone. When actions and observers are invoked, Arez will switch to
the zone in which they were created if it is different from the current zone. The previous zone and any
transaction in the zone will be suspended and and resumed when the action or observer completes.
The current zone can be manipulated by directly interacting with the Arez class. A typical example of use is:
// Create zone
final Zone zone = Arez.createZone();
// Activate the newly created zone and suspend the current zone if any
zone.run( () -> {
// Create new observableValue and ensure it is bound to the current zone
final ObservableValue<Object> observableValue = Arez.context().observable();
// Zone is deactivated when it leaves this block
} );Zones also work with annotation-based components. When components defined by the
@ArezComponent are created, they will invoke Arez.context()
and the component will be bound to the current zone. If a method annotated with @Action or
@Observe is invoked, the method will switch to the zone in which they were created if is
different from the current zone.
An example that uses components is:
// Create zone
final Zone zone = Arez.createZone();
// Activate the newly created zone and suspend the current zone if any
zone.run( () -> {
// Create new component and ensure it is bound to the current zone
final MyComponent myComponent = new Arez_MyComponent();
// Zone is deactivated when it leaves this block
} );