ToolTip events not shown for recursive overlapping QGraphicsItem objects

[TGVF]

Hello folks,
Newbee with event programming (and more generally GUI programming) I am in deep trouble to understand how events and signals-slots are supposed to be managed. Would you recommend some clear and basic course or wiki or book, with nice simple examples using QtGUI?
Precisely, I am presently stuck with a QGraphicsScene object on which are painted a number of QgraphicsPG objects. QgraphicsPG class is based on QGraphics item class. QgraphicsPG objects are constructed and painted recursively (tree-like) , with the same tree structure as their ptr_source member (my type Phygenic*).
I wanted to display as ToolTip some text describing the ptr_source, for instance its ptr_source->nom i.e. its name.
The QgraphicsPG sub-objects have their rectBounds rectangle inside the mother QgraphicsPG object, and they are painted after the mother QgraphicsPG object, assuming this gives them a higher Z-value (correct?) .
Neverthess, tooltip behavior is not what I expect, using the re-implemented QGraphicsPG::hoverEnterEvent as shown below:
I never see the QgraphicsPG sub-objects' ToolTip appearing inside the mother object's RectBounds , but only the mother QgraphicsPG ToolTip itself.

PG_Qt_MainWindow::PG_Qt_MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::PG_Qt_MainWindow)
{
    ui->setupUi(this);
    ui->graphicsView->setScene(&scene);
    ui->graphicsView->show() ;
}
//-----------------------------------------------------
void PG_Qt_MainWindow::on_actionOuvrir_triggered()
{
    QString fileName = QFileDialog::getOpenFileName(this, tr("Ouvrir le fichier..."), QString(),
            tr("Fichiers de modèle brut (*.pgML);") ) ;
// (...) file opened and model constructed, if file is valid
        QGraphicsPG* item= new QGraphicsPG(ptr_modele.back(), position  ) ;
        items.push_back(item);
        scene.addItem(item);
}
//-------------------------------------------------------------------------------------------------------
QGraphicsPG::QGraphicsPG(Phygenic *ptr_pg, Indices2D position, QGraphicsItem *parent, bool develop, bool avecCalcul )
    : rectBoite() , rectTexte(), texte() , flecheEntreeBoite() , flecheSortieBoite() , rectCadre(), rectBounds()
{
    setAcceptHoverEvents(true) ;
    setToolTip( c_QString(" "+ptr_pg->nom) ) ;

    Q_UNUSED(parent) ;
    ptr_source= ptr_pg ;
    Etat_develop= develop ;
    boite= position ;
    cadre= position ;
    flechesInternes.clear() ;
    Indices2D ss_pos ;
    for  ( int iph= 0 ; iph< ptr_source->Nph ; iph++ ) {
       ss_pos.iH= position.iH ; ss_pos.iV= position.iV + iph ;
       ss_qgpg.push_back ( new QGraphicsPG(ptr_source->ph[iph], ss_pos, this, Etat_develop, false ) ) ; 
// NOTE: recursive constructor is called for sub-objects. No calc for sub-objects
    } // next iph
    if (avecCalcul) calculer(boite, develop) ; 
} // fin de QGraphicsPG::QGraphicsPG(Phygenic *ptr_pg, QGraphicsItem *parent, bool develop)
//--------------------------
void QGraphicsPG::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
           QWidget *widget) {
    if ( !Etat_develop || ptr_source->Nph== 0 ) {
        // boite
        painter->setBrush(brush);
        painter->setPen(noir);
        painter->drawRect(rectBoite) ;
// (...)
       // sous-boites
        if (Etat_develop) {
            for  ( int iph= 0 ; iph< ptr_source->Nph ; iph++ ) ss_qgpg.at(iph)->paint(painter, option, widget)  ;
// NOTE: paint function is called recursively here for sub-objects, after the paint operations on the mother object.
        } // end if (Etat_develop)
} // fin de QGraphicsPG::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
//-------------------
void QGraphicsPG::hoverEnterEvent(QGraphicsSceneHoverEvent *event) {
    QToolTip::showText(event->screenPos(), c_QString(" "+ptr_source->nom) ) ;
} // fin de: void QGraphicsPG::hoverEnterEvent(QGraphicsSceneHoverEvent *event)

Apparently, no hoverEnterEvent is triggered for the sub-objects QGraphicsPG although they should be painted on top of the mother object. What did I miss?

[mrjj]

Hi
I cant answer for the HoverEvent but i wondered if you checked with

http://doc.qt.io/qt-5/qgraphicsitem.html#sceneEvent
and
if (event->type() == QEvent::ToolTip) { .... }

[TGVF]

@mrjj
Following your suggestion, this is what I tried :

bool QGraphicsPG::sceneEvent(QEvent *event) {
    bool retour= false ;
    if (event->type() == QEvent::ToolTip) {
        QToolTip::showText(event->screenPos(), c_QString(" "+ptr_source->nom) ) ;
        retour= true ;
    } // end if
    return retour ;
} // fin de: QGraphicsPG::sceneEvent(QEvent *event)

But it won't compile since event->screenPos() is not defined, apparently. Should I cast event somehow (static or dynamic?) to be able to compile.

But may be I should not re-implement any event handler and let Qt do the work for me, (since QToolTip being set in the constructor, everything else should work automatically)? So I tried and removed all specific event handlers from this class, but the result is event worse: there is no longer any ToolTip text displayed...

[TGVF]

@TGVF
Finally, I nailed my bug:
I added what was missing e.g.construction of the base object in the QGraphicsPG constructor, with : QGraphicsItem(parent) instead of declaring Q_USED (parent) .

QGraphicsPG::QGraphicsPG(Phygenic *ptr_pg, Indices2D position, QGraphicsItem *parent, bool develop, bool avecCalcul )
    : QGraphicsItem(parent) , rectBoite() , rectTexte(), texte() , flecheEntreeBoite() , flecheSortieBoite() , rectCadre(), rectBounds()
{
    //setAcceptHoverEvents(true) ;
    setToolTip( c_QString(" "+ptr_pg->nom) ) ;

    //Q_UNUSED(parent) ;
(...)

I also changed the default value of parent to 0 instead of NULL pointer, since the documentation says =0 (isn't it the same, actually?).

public:
   QGraphicsPG(Phygenic* ptr_pg, Indices2D position, QGraphicsItem *parent = 0, bool develop= true, bool avecCalcul= true );

Finally, ToolTip works as desired without need for a hoverEnterEvent handler, nor any other specific event handler!
I feel better now, thanks!

[mrjj]

Hi
Super you found it.
Yes using 0 or NULL is the same.
If you want use something else beside 0 or NULL , then use std::nullptr