apps/tutorials/vostut6.cc

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/* Sixth VOS tutorial.  Child and Property Listeners

   This tutorial covers:
   - Subclassing ChildChangeListener and PropertyListener
   - Handling notify callbacks
   - The VobjectEvent and PropertyEvent classes
   - Adding listeners to Vobjects

   This file (vostut6.cc) is released into the public domain.  No
   restrictions are placed on its use, distribution or inclusion into
   other works.
*/

#include <vos/corelibs/vos/vos.hh>
#include <vos/metaobjects/property/property.hh>

/* A very useful feature of VOS is the ability to get a notification
   callback when something interesting changes, such as the child list
   of a Vobject or the value of a property.  To handle these
   callbacks, you must subclass the appropriate "Listener" class.  The
   Listener defines certain methods which will be called when various
   events happen.  You must override and implement these methods in
   your own class.
 */


// This should be fairly self-explanatory.  The events signaled by
// notifyInserted, notifyReplaced and notifyRemoved correspond to the
// insertChild, setChild and removeChild methods in Vobject.  The
// VobjectEvent class provides specific information about what has happened.

class TutorialChildListener : public ChildChangeListener
{
public:
    virtual void notifyChildInserted(VobjectEvent& e);
    virtual void notifyChildReplaced(VobjectEvent& e);
    virtual void notifyChildRemoved(VobjectEvent& e);
};

void TutorialChildListener::notifyChildInserted(VobjectEvent& e)
{
    // Important note: unlike almost every other method in VOS, the
    // getChild, getParent() etc methods of VobjectEvent do NOT
    // increase the reference count of the Vobject before returning
    // it.  Be careful.

    cout << "Parent " << e.getParent()->getURL().getString()
         << " has added child " << e.getChild()->getURL().getString()
         << "\n at position " << e.getPosition()
         << " with contextual name \"" << e.getContextualName() << "\"\n";
}

void TutorialChildListener::notifyChildReplaced(VobjectEvent& e)
{
    cout << "Parent " << e.getParent()->getURL().getString()
         << " has replaced child " << e.getOldChild()->getURL().getString()
         << "\n with " << e.getNewChild()->getURL().getString()
         << "\n at position " << e.getPosition()
         << " with contextual name \"" << e.getContextualName() << "\"\n";
}

void TutorialChildListener::notifyChildRemoved(VobjectEvent& e)
{
    cout << "Parent " << e.getParent()->getURL().getString()
         << " has removed child " << e.getChild()->getURL().getString()
         << "\n from position " << e.getPosition()
         << " (old contextual name \"" << e.getContextualName() << "\")\n";
}


class TutorialPropertyListener : public PropertyListener
{
public:
    virtual void notifyPropertyChange(const PropertyEvent& e);
};


void TutorialPropertyListener::notifyPropertyChange(const PropertyEvent& e)
{
    // Important note: unlike almost every other method in VOS, the
    // getProperty() method of PropertyEvent does NOT increase the
    // reference count of the Vobject before returning it.  Be
    // careful.

    cout << "Property " << e.getProperty()->getURL().getString()
         << " has changed value from \"" << e.getOldValue()
         << "\" to \"" << e.getNewValue() << "\"\n";

}

int main(int argc, char** argv)
{
    cout << "VOS Tutorial 6\n\n";

    LocalSocketSite localsite(&NoAccessControl::static_);
    localsite.setTimeoutOnSelect(-1);

    Property::registerExtenders();

    vRef<Vobject> sphere = localsite.createMetaObject("sphere", 0);
    vRef<Vobject> tertius = localsite.createMetaObject("tertius", 0);
    vRef<Vobject> quartus = localsite.createMetaObject("quartus", typeid(Property).name(), 0);
    vRef<Vobject> quintus = localsite.createMetaObject("quintus", 0);
    vRef<Vobject> sextus = localsite.createMetaObject("sextus", 0);
    vRef<Vobject> septimus = localsite.createMetaObject("septimus", 0);

    sphere->insertChild(-1, "position", &tertius);
    sphere->insertChild(-1, "orientation", &quartus);


    /* This adds the listener.  Whenever the child list for "sphere"
       changes, the TutorialChildListener class will be called.  Also
       note that when you add a listener, it will immediately be
       called with notifyChildInserted() for each child the Vobject
       currently has.
     */
    sphere->addChildListener(new TutorialChildListener());


    // Mess around with sphere's child list.  This should look
    // familiar :-)

    sphere->insertChild(-1, "radius", &quintus);
    sphere->insertChild(-1, "position", &quartus);
    sphere->insertChild(2, "color", &sextus);
    sphere->setChild(4, "mass", &septimus);
    sphere->removeChild(1);
    sphere->removeChild(-1);

    /* You may use listeners on both local and remote Vobjects. When
       you are set up as a listener for the children of a remote
       vobject, that vobject's child list is cached and considered
       "hot" because any changes to the child list are automatically
       pushed to listeners.  This means that calls to methods like
       Vobject::getChildren() will use the cached copy and not have to
       access the network.  This can be a significant performance win
       for certain applications. */


    // Property listeners work similarly to child listeners.  The
    // listener will be called immediately when first added with the
    // initial value of the property, and the called as further
    // updates happen (from a call to write() or replace()).

    Property* positionproperty = MetaObject::meta_cast<Property*>(&quartus);

    positionproperty->addPropertyListener(new TutorialPropertyListener());

    positionproperty->replace("1 2 3", "text/x-vector-float");

    positionproperty->write(2, "4");

}

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