Subclass doesn't work

[Corvette653]

In my project I have few vertical line so instead of writing:

    QWidget *vertical_line_1 = new QWidget;
    vertical_line_1->setFixedHeight(1);
    vertical_line_1->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
    vertical_line_1->setStyleSheet("background-color: black;");

every time i made subclass:

class VVerticalLine : public QWidget
{
   Q_OBJECT
public:
   VVerticalLine(QWidget *parent = 0) : QWidget(parent) {
       setFixedHeight(1);
       setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
       setStyleSheet("background-color: black;");
   }
   ~VVerticalLine() {}
};

unfortunately, lines created in this way don't appear
Can someone take a look, and tell me where I make a mistake?

[Christian Ehrlicher]

Ok, you have to set Qt::WA_StyledBackground attribute by yourself when you don't use a plain QWidget.

[Christian Ehrlicher]

Please provide a minimal, compilable example on how you use your class when it does not work.

[Corvette653]

mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QGridLayout>
#include <QScreen>

class VVerticalLine : public QWidget
{
   Q_OBJECT
public:
   VVerticalLine(QWidget *parent = 0) : QWidget(parent) {
       setFixedHeight(10);
       setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
       setStyleSheet("background-color: black;");
   }
   ~VVerticalLine() {}
};

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow();
    ~MainWindow();

    QWidget *vertical_line_1 = new QWidget;
    VVerticalLine *vertical_line_2 = new VVerticalLine;

    QWidget *widget = new QWidget;
    QGridLayout *layout = new QGridLayout;
};
#endif // MAINWINDOW_H

mainwindow.cpp:

#include "mainwindow.h"

MainWindow::MainWindow()
{
    showMaximized();
    setGeometry(screen()->geometry());

    vertical_line_1->setFixedHeight(10);
    vertical_line_1->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
    vertical_line_1->setStyleSheet("background-color: black;");

    layout->addWidget(vertical_line_1, 0, 0);
    layout->addWidget(vertical_line_2, 0, 1);

    widget->setLayout(layout);
    setCentralWidget(widget);
}

MainWindow::~MainWindow(){}

It should be clear enough.

[Christian Ehrlicher]

Thx, can confirm this really strange behavior now. Removing Q_OBJECT fixes it (for now, until I find the real problem)

[Christian Ehrlicher]

Ok, you have to set Qt::WA_StyledBackground attribute by yourself when you don't use a plain QWidget.

[JonB]

@Christian-Ehrlicher
This applies to any sub-classed widget where you want it to have a stylesheet background color? You don't have to set it on a supplied sub-class, like say QLabel/QPushbutton etc.? But you do have to set it if you subclass from those?

[Corvette653]

Thank you so much, I would never find it.
@JonB, I have QLabel subclass and it works normally

[JonB]

@Corvette653 said in Subclass doesn't work:

I have QLabel subclass and it works normally

Oh! Now of course QLabel is a subclass of QWidget itself, so might have expected the same problem. Does @Christian-Ehrlicher mean that this Qt::WA_StyledBackground only needs to be added to direct subclasses of QWidget? (And presumably QLabel itself has already done that.)

[Christian Ehrlicher]

From my pov it should not work for QLabel but it does. Need to create a bug report for this.

QLabel is a QFrame so the attribute is set inside QStyleSheetStyle::polish().