CODEWITHSUNDEEP
c++qt
crupest
crupest

Reputation: 122

A simple subclass of QWidget doesn't work as a QWidget

I create a very simple subclass of QWidget like this:

class WorldView : public QWidget
{
    Q_OBJECT
public:
    explicit WorldView(QWidget *parent = 0);

signals:

public slots:
};

WorldView::WorldView(QWidget *parent) : QWidget(parent)
{

}

I create an instance of it in main window like this:

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

protected:
    virtual void resizeEvent(QResizeEvent* event) override;

private:
    WorldView* _worldView;
};

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent)
{
    _worldView = new WorldView(this);
    _worldView->setStyleSheet(QString("* {background-color : black}"));
}

MainWindow::~MainWindow()
{
    delete _worldView;
}

void MainWindow::resizeEvent(QResizeEvent *event)
{
    _worldView->resize(size());
}

But the widget does not show as expected.

I have tried to call show(), but it still doesn't show.

The weird thing is that when I replace WorldView with QWidget, the widget shows.

I don't know why.

Upvotes: 1

Views: 1706

Answers (1)

peppe
peppe

Reputation: 22724

Because stylesheets don't work that way for custom QWidget subclasses.

From https://doc.qt.io/qt-5/stylesheet-reference.html :

QWidget

Supports only the background, background-clip and background-origin properties.

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

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

The above code is a no-operation if there is no stylesheet set.

Warning: Make sure you define the Q_OBJECT macro for your custom widget.

(And, in general, stop using stylesheets.)

Upvotes: 3

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