QTimer在主要功能之外无法正常工作

Question

In short: this piece of code is located in main function and this works just well. This code performs swap on two graphic elements.

        QTimer timer;
        timer.setTimerType(Qt::PreciseTimer);
        timer.setInterval(1000.0/30.0);
        timer.setSingleShot(false);

    // ====================== MOVE 4 in POS of 1 ==========================
        QPointF centre(QLineF(button1->pos(), button4->pos()).pointAt(0.5));
        QPointF positionBut4 = button4->pos();

        MyPointF centreSwap4(0, &positionBut4, &centre);
        button4->myPointF = &centreSwap4;

        QObject::connect(&timer, SIGNAL(timeout()), &centreSwap4, SLOT(updateDownRight()));
        QObject::connect(&centreSwap4, SIGNAL(positionChanged()), button4, SLOT(slotMoveCircle()));

    // ====================== MOVE 4 in POS of 1 ==========================

    // ====================== MOVE 1 in POS of 4 ==========================
        QPointF positionBut1 = button1->pos();

        MyPointF centreSwap1(0, &positionBut1, &centre);
        button1->myPointF = &centreSwap1;

        QObject::connect(&timer, SIGNAL(timeout()), &centreSwap1, SLOT(updateUpLeft()));
        QObject::connect(&centreSwap1, SIGNAL(positionChanged()), button1, SLOT(slotMoveCircle()));
    // ====================== MOVE 1 in POS of 4 ==========================
        timer.start();

        QTimer::singleShot(3000, Qt::PreciseTimer, &timer, SLOT(stop()));

But when I want to put this piece of code out of main into a function (in order to shorten the code and perform swap on elements by just giving pointers to them) QTimer refuses to work(says it's active but timeout is not triggered):

    void animateSwap(QGraphicsRectWidget *w1, QGraphicsRectWidget *w2, QTimer &timer)
    {
        QGraphicsRectWidget *button4, *button1;
        if (w1->x() > w2->x())
        {
                button4 = w2;
                button1 = w1;
        }
        else
        {
            button4 = w1;
            button1 = w2;
        }
        // ====================== MOVE w2  in POS of w1 ==========================
        QPointF centre(QLineF(button1->pos(), button4->pos()).pointAt(0.5));
        QPointF positionBut4 = button4->pos();

        MyPointF centreSwap4(0, &positionBut4, &centre);
        button4->myPointF = &centreSwap4;

        QObject::connect(&timer, SIGNAL(timeout()), &centreSwap4, SLOT(updateDownRight()));
        QObject::connect(&centreSwap4, SIGNAL(positionChanged()), button4, SLOT(slotMoveCircle()));

        // ====================== !MOVE w2 in POS of w1 ==========================

        // ====================== MOVE w1 in POS of w2 ==========================
        QPointF positionBut1 = button1->pos();

        MyPointF centreSwap1(0, &positionBut1, &centre);
        button1->myPointF = &centreSwap1;

        QObject::connect(&timer, SIGNAL(timeout()), &centreSwap1, SLOT(updateUpLeft()));
        QObject::connect(&centreSwap1, SIGNAL(positionChanged()), button1, SLOT(slotMoveCircle()));
        // ====================== MOVE w1 in POS of w2 ==========================
        timer.start();

        qDebug() << timer.isActive();

        QTimer::singleShot(3000, Qt::PreciseTimer, &timer, SLOT(stop()));
    }

UPDATE: Now it works:

    void animateSwap(QGraphicsRectWidget *w1, QGraphicsRectWidget *w2, QTimer &timer, int cycles = 1)
    {
        QGraphicsRectWidget *button4, *button1;
        if (w1->x() > w2->x())
        {
                button4 = w2;
                button1 = w1;
        }
        else
        {
            button4 = w1;
            button1 = w2;
        }
        // ====================== MOVE w2  in POS of w1 ==========================
        QPointF centre(QLineF(button1->pos(), button4->pos()).pointAt(0.5));
        QPointF positionBut4 = button4->pos();

        MyPointF *centreSwap4 = new MyPointF(0, &positionBut4, &centre);
        button4->myPointF = centreSwap4;

        QObject::connect(&timer, SIGNAL(timeout()), centreSwap4, SLOT(updateDownRight()));
        QObject::connect(centreSwap4, SIGNAL(positionChanged()), button4, SLOT(slotMoveCircle()));

        // ====================== !MOVE w2 in POS of w1 ==========================

        // ====================== MOVE w1 in POS of w2 ==========================
        QPointF positionBut1 = button1->pos();

        MyPointF *centreSwap1 = new MyPointF(0, &positionBut1, &centre);
        button1->myPointF = centreSwap1;

        QObject::connect(&timer, SIGNAL(timeout()), centreSwap1, SLOT(updateUpLeft()));
        QObject::connect(centreSwap1, SIGNAL(positionChanged()), button1, SLOT(slotMoveCircle()));
        // ====================== MOVE w1 in POS of w2 ==========================
        timer.start();

        qDebug() << timer.isActive();

        QTimer::singleShot(3000 * cycles, Qt::PreciseTimer, &timer, SLOT(stop()));
    }

Answer 1

You are connecting the timeout() signal of the timer to eg

MyPointF centreSwap1(0, &positionBut1, &centre);

which is an object on the stack, and therefore local to the function and is deleted the moment the function finishes. Qt disconnects a connection if one of the objects (sender, receiver) is deleted, so the moment the timer finishes there is nothing connected to its timeout() signal.