Observers
Applications can be notified when the state of a manager changes. This notification mechanism is based on IlvManagerObserver, a subclass of IlvObserver. Observers are created by the application and set on the manager. The manager is in charge of sending messages to the observer under certain circumstances called reasons.
Notification messages are classified by their reason into different categories. An observer can choose to receive messages of one or several categories by setting its interest mask. The manager will only send a message to the observer if the notification reason belongs to a category of the observer interest mask. These categories are shown in Notification Categories:
Category Description | Mask |
|---|---|
General | IlvMgrMsgGeneralMask |
Manager view | IlvMgrMsgViewMask |
Manager layer | IlvMgrMsgLayerMask |
Manager contents | IlvMgrMsgContentsMask |
Object geometry | IlvMgrMsgObjectGeometryMask |
An application wishing to get notification messages must define a subclass of IlvManagerObserver and overload the virtual member function update. In this member function, the observer receives an instance of IlvManagerMessage, or a subclass, containing the reason and additional relevant information about the notification.
General Notifications
This category concerns general notifications on the managers.
Interest mask: IlvMgrMsgGeneralMask
Delete the managerReason: IlvMgrMsgDelete
Message type: IlvManagerMessage
Manager View Notifications
This category concerns notifications on operations performed on manager views.
Interest mask: IlvMgrMsgViewMask
Add a view to the managerReason: IlvMgrMsgAddView
Message type: IlvManagerAddViewMessage
Remove a view from the managerReason: IlvMgrMsgRemoveView
Message type: IlvManagerRemoveViewMessage
Set an interactor on a viewReason: IlvMgrMsgSetInteractor
Message type: IlvManagerSetInteractorMessage
Set a transformer on a viewReason: IlvMgrMsgSetTransformer
Message type: IlvManagerSetTransformerMessage
Manager Layer Notifications
This category concerns notifications on operations performed on manager layers.
Interest mask: IlvMgrMsgLayerMask
Add a layer to the managerReason: IlvMgrMsgAddLayer
Message type: IlvManagerLayerMessage
Remove a layer from the managerReason: IlvMgrMsgRemoveLayer
Message type: IlvManagerLayerMessage
Change the index of a layerReason: IlvMgrMsgMoveLayer
Message type: IlvManagerMoveLayerMessage
Swap indexes between two layersReason: IlvMgrMsgSwapLayer
Message type: IlvManagerSwapLayerMessage
Set the name of a layerReason: IlvMgrMsgLayerName
Message type: IlvManagerLayerNameMessage
Set the visibility of a layerReason: IlvMgrMsgLayerVisibility
Message type: IlvManagerLayerVisibilityMessage
Set the selectabililty of a layerReason: IlvMgrMsgLayerSelectability
Message type: IlvManagerLayerMessage
Manager Contents Notifications
This category concerns notifications on the changes in the contents of managers.
Interest mask: IlvMgrMsgContentsMask
Add a graphic object to the managerReason: IlvMgrMsgAddObject
Message type: IlvManagerContentsMessage
Remove a graphic object from the managerReason: IlvMgrMsgRemoveObject
Message type: IlvManagerContentsMessage
Set the layer of a graphic objectReason: IlvMgrMsgObjectLayer
Message type: IlvManagerObjectLayerMessage
Graphic Object Geometry Notifications
This category concerns notifications on a change of geometry of the objects (for example, move, resize, and rotate).
Interest mask: IlvMgrMsgObjectGeometryMask
Change the geometry of a graphic objectReason: IlvMgrMsgObjectGeometry
Message type: IlvManagerObjectGeometryMessage
Example
Here is the implementation of an observer that receives notifications on adding or removing layers and views.
class MyManagerObserver : public IlvManagerObserver { public: MyManagerObserver(IlvManager* manager) : IlvManagerObserver(manager, IlvMgrMsgLayerMask | IlvMgrMsgViewMask) {} virtual void update(IlvObservable* o, IlAny arg); }; |
The update member function:
void MyManagerObserver::update(IlvObservable* obs, IlAny arg) { IlvManager* manager = ((IlvManagerObservable*)obs)->getManager(); switch(((IlvManagerMessage*) arg)->_reason) { // __ Notification on manager view case IlvMgrMsgAddView: IlvPrint("Add view notification"); break; case IlvMgrMsgRemoveView: IlvPrint("Remove view notification"); break; // __ Notification on manager layer case IlvMgrMsgAddLayer: IlvPrint("Add layer notification: %d", ((IlvManagerLayerMessage*)arg)->getLayer()); break; case IlvMgrMsgRemoveLayer: IlvPrint("Remove layer notification: %d", ((IlvManagerLayerMessage*)arg)->getLayer()); break; default: IlvPrint("Unhandled notification"); break; } } |
To attach the observer to the manager:
MyManagerObserver* observer = new MyManagerObserver(manager);
Published date: 05/24/2022
Last modified date: 02/24/2022
