How can I set the background with a usleep()?

Question

I call the function of background two times with two different backgrounds. I setup usleep(1000) but does not work. My system is linux and I am run Qt 4.8.

main.cpp

MainWindow w;
w.setBg('A');
usleep(1000);
w.setBg('B');

In the mainwindow.cpp there is setBg(char c) with switch to select between two backgrounds.

How can I call the first switch with usleep then switch to the other?

Should I reload my widget?

Answer 1

The tasks that block the inner loop of the GUI are not correct for this type of tasks, as in your case it is usleep, it is advisable to use a QTimer as shown below:

/*Qt5*/
MainWindow w;
w.setBg('A');
w.show();

QTimer::singleShot(1 /*in ms*/, [&w](){
    w.setBg('B');
});

/*Qt4*/
/*on MainWindow*/

private slots:
    void mySlot(){
        setBg('B');
    }
/*constructor*/
    QTimer::singleShot(1000, this, SLOT(mySlot()));