Event Bus
The Event Bus is uses to manage event subscriptions and ensure events are emitted to the correct modules.
Subscribing to an Event
Before we can take action when an event is emitted, we need to subscribe to it. This is typically done in the Boot() method of an extension module.
// show code to subscribe to an event from within an extension module with the boot method
public class MissileGuidanceModule : BaseExtensionModule
{
// show code to emit an event from within an extension module
public override void Boot()
{
// subscribe using the Event Bus module
Mother.GetModule<EventBus>().Subscribe<MissileLaunchedEvent>(this);
// Or via a helper method
Subscribe<MissileLaunchedEvent>();
}
}
Emitting an Event
We can emit an event by using the Emit() method. Any module that has subscribe to this event will receive it.
// show code to emit an event from within an extension module
public void Launch()
{
// Do launch stuff
// ...
Mother.GetModule<EventBus>().Emit(new MissileLaunchedEvent());
}
Since this is a very common activity, the BaseExtensionModule class provides an accessor method:
public class MissileGuidanceModule : BaseExtensionModule
{
public void Launch()
{
// Do launch stuff
// ...
Emit<MissileLaunchedEvent>();
}
}
Listening for an Event
Extension modules can override the HandleEvent() method to listen for events to which they have subscribed. This method will be called whenever an event is emitted to this module.
public class MissileGuidanceModule : BaseExtensionModule
{
// Handle the event
public override void HandleEvent(IEvent e, object eventData)
{
if (e is MissileLaunchedEvent)
ArmWarhead();
}
// Do something as a result
void ArmWarhead() { }
}
Unsubscribing from an Event
To unsubscribe from an event, you can use the Unsubscribe method of the EventBus module. Perhaps in our example above, it makes sense to unsubscribe from the MissileLaunchedEvent once the missile has been launched.
public class MissileGuidanceModule : BaseExtensionModule
{
// Handle the event
public override void HandleEvent(IEvent e, object eventData)
{
if (e is MissileLaunchedEvent)
{
// Unsubscribe from the event
Mother.GetModule<EventBus>().Unsubscribe<MissileLaunchedEvent>(this);
// Do more stuff
// ...
}
}
}
You can easily check if a module is subscribed to an event by using the IsSubscribed method of the EventBus module.
MissileGuidanceModule module = Mother.GetModule<MissileGuidanceModule>();
bool subscribed = Mother.GetModule<EventBus>()
.IsSubscribed<MissileLaunchedEvent>(module);