QGraphicsItemText won't detect mouse flags

Question

What I'm trying to do is pretty simple, when the mouse is over the qgraphicsitem I want it to change it's text value. Later on I want to use this to pop-up text when I click an image (i.e. the info of the image)

Here's my code so far:

#include <QtGui/QApplication>
#include <QtGui/QGraphicsItem>
#include <QtGui/QGraphicsTextItem>
#include <QtGui/QGraphicsScene>
#include <QtGui/QGraphicsView>
#include <QtGui/QPixmap>

int main( int argc, char * * argv )
{
    QApplication      app( argc, argv );
    QGraphicsScene    scene;
    QGraphicsView     view( &scene );

    QGraphicsTextItem text( "this is my text");
    scene.addItem(&text);
    scene.setActivePanel(&text);
    text.setFlags(QGraphicsItem::ItemIsSelectable | QGraphicsItem::ItemIsFocusable);
    text.setAcceptHoverEvents(true);
    text.setAcceptTouchEvents(true);
    if (text.isUnderMouse() || text.isSelected()){
        text.setPlainText("test");
    }
    view.show();

    return( app.exec() );
}

Some people use double-click events but I was hoping not to use them, but... if that's the only way to get the job done then it's ok.

Answer 1

This code block:

if (text.isUnderMouse() || text.isSelected()){
    text.setPlainText("test");
}

is run exactly once, before your view is even shown; so this has absolutely no chance of doing what you expect it to.

You'll need to do a bit more work for that, namely create a custom subclass of QGraphicsTextItem and override the appropriate event handlers.

Here's how you could do that to handle changing text when hovering:

class MyTextItem: public QGraphicsTextItem
{
    public:
        MyTextItem(QString const& normal, QString const& hover,
                   QGraphicsItem *parent=0)
            : QGraphicsTextItem(normal, parent), normal(normal), hover(hover)
        {
        }

    protected:
        void hoverEnterEvent(QGraphicsSceneHoverEvent *)
        {
            setPlainText(hover);
        }
        void hoverLeaveEvent(QGraphicsSceneHoverEvent *)
        {
            setPlainText(normal);
        }
    private:
        QString normal, hover;

};

Add that to your code, and change the text declaration to:

MyTextItem text("this is my text", "test");

and it should do what you expect.