Qt android paintevent problem？
MainWindow::MainWindow(QWidget *parent) :
void MainWindow::paintEvent(QPaintEvent *event)
painter.drawLine(QPoint(10,10),QPoint(100,400)); //drawLine() Without any effect, without any display？
painter.drawRect(100,100,100,100);//drawRect() Without any effect, without any display？
//On the QT Android 6 system。
//drawLine()，drawRect() Without any effect, without any display？
//How to use painter()??
Usually, you are not supposed to draw on QMainWindow directly. You should only draw on elements placed on the window.
Also, when you claim that a function call does not have any effect, check first that it gets executed - It may well be that your paintEvent doesn't get called, lacking a reason to update it... (there should be an update() call generated somewhere).