Why Can't I change background-color in QWidget using CSS?

TomNow99

Hello,

I have 3 classes:
myWid
newWid
widLab

In newWid and widLab I only create QGridLayouts and setLayouts(), nothing more:

newWid::newWid(QWidget *parent):QWidget(parent)
{
    grid = new QGridLayout;
    setLayout(grid);
}

widLab::widLab(QWidget *parent):QWidget(parent)
{
    grid = new QGridLayout;
    setLayout(grid);
}

In class myWid In constructor I have:

myWid::myWid(QWidget *parent): QWidget(parent)
{
    grid = new QGridLayout;

    nw = new newWid;
    wl = new widLab;

    setLayout(grid);

    grid->addWidget(nw,0,0,1,1);
    grid->addWidget(wl,0,1,1,1);
    setStyleSheet("QWidget {background-color:red}");
    nw->setStyleSheet("QWidget {background-color:red}");
    wl->setStyleSheet("QWidget {background-color:red}");
}

And that 3 classes don't have any other methods. Only constructors.

Next in mainWindow constructor ( which doesn't have other methods ) I have:

    mw = new myWid;

    grid = new QGridLayout;
    centralWidget()->setLayout(grid);
    grid->addWidget(mw);

Classes myWid, newWid, widLab inherits QWidget.

And there is no color red. I try use that setStyleSheet in constructors too, but with the same result ( no result ).

Of course when I add to grids in newWid and widLab widgets I see them, but no on the red background.

Bonnie

A subclassed QWidget need to either call

setAttribute(Qt::WA_StyledBackground);

or reimplement paintEvent as stated in the doc:

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

sierdzio

I guess that when you assign grid->addWidget(mw); your child widgets inherit the QSS from parent and thus loose your custom stylesheet. Setup your UI first, then set QSS.

TomNow99

@sierdzio
In mainWindow constructor I add ( after grid->addWidget(mw) )

     QTimer::singleShot(100,this, SLOT(x()));

and the x() slot looks like:

void MainWindow::x()
{
    mw->setStyleSheet("QWidget {background-color:red}");
}

but still doesn't get the red color.

Bonnie

A subclassed QWidget need to either call

setAttribute(Qt::WA_StyledBackground);

or reimplement paintEvent as stated in the doc:

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

TomNow99

@Bonnie Yes, now it works! Thank you. But when I tested something like:

in MainWindow

    someObjectWhichInheritsQWidget = new someClass;
    someObjectWhichInheritsQWidget -> setStyleSheet("QWidget {background-color:red}");

    grid = new QGridLayout;
    centralWidget()->setLayout(grid);
    grid->addWidget(someObjectWhichInheritsQWidget);

and in this someObjectWhichInheritsQWidget didn't had any other grids / widgets ( like in myWid ) everything was ok.

So when I have to add

setAttribute(Qt::WA_StyledBackground);

?

Bonnie

@TomNow99
AFAIK, a window or a QFrame doesn't need to add extra codes.
Not sure what your case is.

TomNow99

@Bonnie You are right.

I create 2 widgets in mainWindow:
QWidget object
myClassWhichInheritsQWidget object

In QWidget I don't need add extra code, but in myClassWhi.... object I have to add that

setAttribute(Qt::WA_StyledBackground);

Thank you

Solved Why Can't I change background-color in QWidget using CSS?