Observers

2D Graphics > Managers > Advanced Manager Features > Observers

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:

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 manager

Reason: 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 manager

Reason: IlvMgrMsgAddView

Message type: IlvManagerAddViewMessage

Remove a view from the manager

Reason: IlvMgrMsgRemoveView

Message type: IlvManagerRemoveViewMessage

Set an interactor on a view

Reason: IlvMgrMsgSetInteractor

Message type: IlvManagerSetInteractorMessage

Set a transformer on a view

Reason: 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 manager

Reason: IlvMgrMsgAddLayer

Message type: IlvManagerLayerMessage

Remove a layer from the manager

Reason: IlvMgrMsgRemoveLayer

Message type: IlvManagerLayerMessage

Change the index of a layer

Reason: IlvMgrMsgMoveLayer

Message type: IlvManagerMoveLayerMessage

Swap indexes between two layers

Reason: IlvMgrMsgSwapLayer

Message type: IlvManagerSwapLayerMessage

Set the name of a layer

Reason: IlvMgrMsgLayerName

Message type: IlvManagerLayerNameMessage

Set the visibility of a layer

Reason: IlvMgrMsgLayerVisibility

Message type: IlvManagerLayerVisibilityMessage

Set the selectabililty of a layer

Reason: 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 manager

Reason: IlvMgrMsgAddObject

Message type: IlvManagerContentsMessage

Remove a graphic object from the manager

Reason: IlvMgrMsgRemoveObject

Message type: IlvManagerContentsMessage

Set the layer of a graphic object

Reason: 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 object

Reason: 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);

Version 6.1