Custom Widget is not visible in Widget window

devillIsHeree

I have created my own custom widget class, the code is below:

class myWidget : public QWidget
{
    Q_OBJECT
public:
    explicit myWidget(QWidget*parent=nullptr): QWidget(parent){}
    void enterEvent(QEvent *event) override
    {
        Q_UNUSED(event);
        qDebug()<<"Entered";
    }
};

In widget.cpp I have created it's instance, like below

myWidget *w;

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    w=new myWidget(this);
    w->setStyleSheet("background-color: rgb(138, 226, 52);");
    w->setGeometry(10,10,100,100);
    w->show();
}

As you can see my object is child of the thiswidgetwindow but whenever I run the program it won't be visible to me in the window but when i go to top bottom i can see the console output of mine Entered, So it is present in my Widget window but I am not able to see it even I have set the background color as green, If I just use the Qt GUI to add one Widget into the form and set the background color and run the code then that Widget which I added from the GUI is visible but My Widget which i created by my own custom widget is not visible.

mrjj

@devillIsHeree
Hi
How do your paintEvent look like for myWidget?
It has to be like

 void CustomWidget::paintEvent(QPaintEvent *)
 {
     QStyleOption opt;
     opt.init(this);
     QPainter p(this);
     style()->drawPrimitive(QStyle::PE_Widget, &opt, &p, this);
 }

to use a stylesheet.

devillIsHeree

@mrjj Thanks it works, Can you please explain the logic behind it? because if we do the same without using my own class it works but when I do the same by inheriting I have to modify the paintEvent as you told.

mrjj

@devillIsHeree
Hi
For some reason, the QWidget::paintEvent is empty so once subclassed
its not doing anything. I never really found out how come plain QWidget can
work but I guess that QStyle somehow makes it possible as long its a plain QWidget.
So when we subclass it, we have to draw using QStyle to make a stylesheet take effect.

Bonnie

@devillIsHeree
I don't actually know the logic, it is just in the documentation

If you subclass from QWidget, you need to provide a paintEvent for your custom QWidget as below:
...

And if you feel it a little annoying to write a paintEvent, there's a trick that I was told by @JonB :

setAttribute(Qt::WA_StyledBackground);

add this in your custom widget's constructor.