I am making a list of blue rectangles and then try to change color of them one by one to the end of the list. Here is my source code:

traverse() in dialog.cpp
Qt Code: 
  1. void Dialog::traverse()
  2. {
  3.     Node *cur = head;
  4.     while (cur)
  5.     {
  6.         colorAnimation = new QPropertyAnimation(cur->square, "color");
  7.         colorAnimation->setDuration(4000);
  8.         colorAnimation->setKeyValueAt(0.0, RED);
  9.         colorAnimation->setKeyValueAt(0.9, RED);
  10.         colorAnimation->setKeyValueAt(1.0, CYAN);
  11.         colorAnimation->start();
  12.  
  13.         clock_t waiter = clock() + 4 * CLOCKS_PER_SEC;
  14.         while (clock() < waiter);
  15.         cur = cur->next;
  16.     }
  17. }
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square.h
Qt Code: 
  1. const int CYAN = 0;
  2. const int RED = 1;
  3. class Square : public QObject, public QGraphicsItem
  4. {
  5.     Q_OBJECT
  6.     Q_PROPERTY(int color MEMBER color WRITE setColor)
  7. public:
  8.     Square();
  9.     Square(int n);
  10.     ~Square();
  11.     QRectF boundingRect() const;
  12.     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
  13.     void setColor(int newColor);
  14. private:
  15.     int color;
  16.     int order;
  17. };
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square.cpp
Qt Code: 
  1. #include "square.h"
  2.  
  3. Square::Square()
  4. {
  5.     color = CYAN;
  6.     order = 0;
  7. }
  8.  
  9. Square::Square(int n)
  10. {
  11.     color = CYAN;
  12.     order = n;
  13. }
  14.  
  15. Square::~Square()
  16. {
  17. }
  18.  
  19. QRectF Square::boundingRect() const
  20. {
  21.     return QRectF(X_START + order*HDISTANCE, Y_START, B_WIDTH, HEIGHT);
  22. }
  23.  
  24. void Square::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
  25. {
  26.     QRectF rect = QRectF(X_START + order*HDISTANCE + LINE, Y_START, WIDTH, HEIGHT);
  27.     QPen pen(Qt::blue);
  28.     pen.setCapStyle(Qt::RoundCap);
  29.     QBrush brush(Qt::cyan);
  30.  
  31.     if (color == RED)
  32.     {
  33.         brush.setColor(Qt::red);
  34.     }
  35.     else if (color == CYAN)
  36.     {
  37.         brush.setColor(Qt::cyan);
  38.     }
  39.  
  40.     painter->fillRect(rect, brush);
  41.     painter->drawRect(rect);
  42. }
  43.  
  44. void Square::setColor(int newColor)
  45. {
  46.     color = newColor;
  47.     update();
  48. }
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It happens to be a group of rectangles changing to red at the same time. I think it is because the update() function doesn't repaint the item immediately, but I can not use the repaint() function to modify a graphics item. Can anyone suggest a way to repaint the item immediately? Thanks you very much.