Change circle colour every 5 seconds - c++

Question

I try to create a green circle which every 5 seconds disappears.
Actually, I have the green circle created with the QPainter method. I tried QTimer and others methods but I can't find the good solution.
I overrided the paintEvent function like this :
void MainWindow::paintEvent(QPaintEvent *)
{
QPainter painter(this);
Qt::BrushStyle style = Qt::SolidPattern;
QBrush brush(Qt::green, style);
painter.setRenderHint(QPainter::Antialiasing);
painter.setBrush(brush);
painter.drawEllipse(525, 5, 50, 50);
}
MainWindow::MainWindow() : QWidget()
{
QTimer *ledtimer = new QTimer(this);
connect(ledtimer, SIGNAL(timeout()), this, SLOT(run_led()));
ledtimer->start(5000);
}
I tried to do something like this, but when i'm using run_led, it tells that painter is already removed (i tried in MainWindow class).
I understand the signal function and the timer, I used it in another files, so some tips would be appreciated. Am I supposed to use timers to make circles wink ?

Answer 1

Define a flag boolean that changes every 5 seconds and in paint use a brush as global variable
void MainWindow::paintEvent(QPaintEvent *)
{
....
QBrush brush(myBrush, style);
...
}
and in slot (run_led)
void MainWindow::run_led()
{
c != true;
if(c)
{
myBrush=Qt::green;
}
else
{
myBrush=Qt::gray;
}
}

Answer 2

Assuming your MainWindowinherits QMainWindow
MainWindow::paintEvent(QPaintEvent *) is a function that tells the systems to render your window.
So I let you guess what goes wrong when you override it like this.
But you can put the drawing in a QWidget made for this : QGraphicsView which displays the content of QGraphicsScene .
You should create a slot to do what you want, like this :
void MainWindow::on_led_timer_timeout(){
/*
Do stuff the the QGraphicsScene or QGraphicsView
*/
}
And then connect the correct signal of your QTimer to it :
connect(ledtimer, &QTimer::timeout, this, &MainWindow::on_led_timer_timeout);

Answer 3

class QSimpleLed : public QWidget
{
Q_OBJECT
Q_PROPERTY(QColor color READ color WRITE setColor)
public:
using QWidget::QWidget;
void setColor(const QColor& c) {
if (m_color != m) {
m_color = m;
update();
}
}
QColor color() const;
void paintEvent(QPaintEvent *) override;
private:
QColor m_color;
}
Implementation above should be obvious.
int main(int argc, char* argv[])
{
QApplication app{argc, argv};
QSimpleLed led;
auto animation = new QPropertyAnimation(&led, "color");
animation->setStartValue(Qt::red);
animation->setEndValue(Qt::green);
animation->setLoopCount(-1);
animation->setDuration(5000);
animation->start();
led.show();
return app.exec();
}