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detect if mouse buttons are pressed when sliding into widget



  • I want to do the following:

    I have two exactly the same widgets which are next to each other. I want to push down a mouse button in the first one and then slide into the second widget to perform a action there. So the second widget should detect that the mouse button is down and i slided in.

    However it looks like the second widget never gets informed that i slided into it. Strangely I can see the slide in if i go out of the first widget and back in.

    void Cell::mouseMoveEvent(QMouseEvent *event)
    {
        if(!mouseIsOutside(event)  &&
                event->buttons() & Qt::LeftButton ) {
    
            qDebug() << "Entered";
    
        }
    }
    
    bool Cell::mouseIsOutside(QMouseEvent *event)
    {
        auto pos = event->pos();
        auto rect = this->rect();
    
        if(pos.x() < rect.x()) {
            return true;
        }
        if(pos.x() > rect.x() + rect.width()) {
            return true;
        }
        if(pos.y() < rect.y()) {
            return true;
        }
        if(pos.y() > rect.y() + rect.height()) {
            return true;
        }
        return false;
    }
    

  • Moderators

    Widgets grabMouse() on mouse press meaning all following mouse events go to that pressed widget until mouse is released. This is to ensure that widgets properly update their state. For example it would be very difficult to handle clicks correctly if press went to one widget and release to another.

    What you can do is installEventFilter() on both widgets and handle their presses, moves and releases there. Since you would get events from both widgets, no matter which grabbed the mouse, you could there check over which widget the event occurred.

    Btw. you don't need to all those bound checks manually. QRect has a handy method contains(), so you can just do rect.contains(point);

    Just be mindful that the event->pos() is in coordinates of the widget that received the event, so if you want to go with the event filter you will need to map the point and rect coordinates to the same coord space, e.g. the global space:

    event->globalPos() will give you the mouse position in global space
    QRect r(widget->mapToGlobal(QPoint(0,0)), widget->size()) will give you the widget rectangle in global space



  • How can I distinguish between mouseMoveEvent , mouseReleaseEvent and mousePressEvent in the event filter?


  • Moderators

    Inside the event handler you can check the event type:

    bool YourClass::eventFilter(QObject *watched, QEvent *event)
    {
       if(event->type() == QEvent::MouseButtonPress)
       {
          QMouseEvent* mouse_event = static_cast<QMouseEvent*>(event);
          // do something...
       }
    
       return false; // means handle event as usual
    }
    

    ...and so on for other event types. Here are all possible event types.



  • @Chris-Kawa said in detect if mouse buttons are pressed when sliding into widget:

    if(event->type() == QEvent::MouseButtonPress)
    {
    QMouseEvent* mouse_event = static_cast<QMouseEvent*>(event);
    // do something...
    }

    Ok I have one more concern. Before i handled mouseMoveEvent , mouseReleaseEvent and mousePressEvent in the Cell class. To implement them I used private functions and members of the Cell class. To implement the behaviour now i have to make them public or frind with the Event filter class. Doesn't that break encapusulation?


  • Moderators

    @sandro4912 said in detect if mouse buttons are pressed when sliding into widget:

    To implement the behaviour now i have to make them public or frind with the Event filter class.

    Can't you just call a public function on that Cell class that will call all those private things?



  • i tryed it out however i still have the same issue:

    
    bool CellInputHandler::eventFilter(QObject *watched, QEvent *event)
    {
        auto cell = qobject_cast<Cell *>(watched);
    
        if(event->type() == QEvent::MouseButtonPress){
           auto mouse_event = static_cast<QMouseEvent*>(event);
           cell->handleMousePressEvent(mouse_event);
           return true;
        }
        if(event->type() == QEvent::MouseButtonRelease){
           auto mouse_event = static_cast<QMouseEvent*>(event);
           cell->handleMouseReleaseEvent(mouse_event);
           return true;
        }
        if(event->type() == QEvent::MouseMove) {
            auto mouse_event = static_cast<QMouseEvent*>(event);
            QRect rect{cell->mapToGlobal(QPoint(0, 0)), cell->size()};
    
            if(rect.contains(mouse_event->globalPos())) {
    
                if(mouse_event->buttons() & Qt::LeftButton &&
                    mouse_event->buttons() & Qt::RightButton) {
    
                    cell->handleMouseMoveEventInside(mouse_event);
                }
            }
            else {
                cell->handleMouseMoveEventOutside(mouse_event);
            }
            return true;
        }
        return false;
    }
    
    
    

    Press and Release seem to work fine like they already did. However the move still only detects one widget.

    In Cell i added this:

    void Cell::handleMouseMoveEventInside(QMouseEvent *event)
    {
            qDebug() << "Entered";
    }
    
    void Cell::handleMouseMoveEventOutside(QMouseEvent *event)
    {
            qDebug() << "Left";
    }
    

    Still i only see Entered and Left from the widget i first clicked down the mouse buttons



  • @sandro4912 It sounds a bit like a drag-and-drop operation to me. Wouldn't that work for you?



  • You mean using drag and drop in the event filter to transfer that mouse buttons are pressed both?


  • Lifetime Qt Champion

    @sandro4912
    Hi
    Do you have
    setMouseTracking(true);
    on widget 2 ?



  • @mrjj said in detect if mouse buttons are pressed when sliding into widget:

    Hi

    Yes it is enabled on both widgets(they are the same widgets)


  • Lifetime Qt Champion

    @sandro4912
    Ok. :)
    was just a shot.



  • I really wonder how the issue could get solved. Annother Information i maybe forgot to tell.

    Both widgets are inside annother widget. Could that help?


  • Lifetime Qt Champion

    @sandro4912
    Hi
    The issue is that you only see

    event->type() == QEvent::MouseMove

    for one of the widgets ?



  • @mrjj I believe that you need to set a variable, addressable from each cell, that indicates that the mouse button has been pressed. My concern with this is that what happens if the mouse button is released in another widget? Hover events might be helpful.


  • Moderators

    The problem is you're checking the rectangle of the wrong widget. As I said the widget grabs mouse when you press, so cell is always gonna be the widget that gets the events, the one you pressed on, not the one you're hovering over.

    You need to get the rectangle of the other widget from somewhere.

    Here's a little working example. Maybe you'll find it useful:

    #include <QApplication>
    #include <QPushButton>
    #include <QHBoxLayout>
    #include <QEvent>
    #include <QDebug>
    
    struct FilterClass : public QObject
    {
        bool eventFilter(QObject*, QEvent* evt)
        {
            if (evt->type() == QEvent::MouseMove)
            {
                auto move_evt = static_cast<QMouseEvent*>(evt);
                if (move_evt->buttons().testFlag(Qt::LeftButton) &&
                    move_evt->buttons().testFlag(Qt::RightButton))
                    qDebug() << "Mouse over" << qApp->widgetAt(move_evt->globalPos());
            }
    
            return false;
        }
    };
    
    int main(int argc, char *argv[])
    {
        QApplication a(argc, argv);
    
        FilterClass filter;
        QWidget w;
        w.setLayout(new QHBoxLayout());
        w.layout()->addWidget(new QPushButton("Button 1"));
        w.layout()->addWidget(new QPushButton("Button 2"));
        for (auto c : w.children()) c->installEventFilter(&filter);
    
        w.show();
        return a.exec();
    }
    


  • I could solve the issue with the example code.

    I had to add a member which remembers the last cell in the event filer. Than i could solve my Issue like this:

    if(event->type() == QEvent::MouseMove) {
        auto mouse_event = static_cast<QMouseEvent*>(event);
        QRect rect{cell->mapToGlobal(QPoint(0, 0)), cell->size()};
    
        if(mouse_event->buttons().testFlag(Qt::LeftButton) &&
            mouse_event->buttons().testFlag(Qt::RightButton)) {
    
            auto widget = qApp->widgetAt(mouse_event->globalPos());
    
            if(widget) {
                auto currentCell = qobject_cast<Cell *>(widget);
    
                if(!currentCell) {
                    if(mLastCell) {
                        mLastCell->handleMouseMoveEventOutside(mouse_event);
                    }
                    mLastCell = nullptr;
                    return true;
                }
    
                if(currentCell != mLastCell) {
                    if(mLastCell) {
                        mLastCell->handleMouseMoveEventOutside(mouse_event);
                    }
                    currentCell->handleMouseMoveEventInside(mouse_event);
                    mLastCell = currentCell;
                }
            }
            return true;
        }
    }

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