stylesheet无效

//sheetstyle file, style.css
QWidget#setting_widget
{
    background-color: white;
}

//child widget
class CSubWidget : public QWidget
{
    Q_OBJECT
public:
    explicit CSettingWidget(QWidget *parent = 0);
};
CSettingWidget::CSettingWidget(QWidget *parent)
    : QWidget(parent)
{
    setWindowFlags(Qt::WindowStaysOnTopHint);
    setObjectName("subwidget");
}

//main widget
class MainWindow : public QWidget
{
    Q_OBJECT
public:
    ~MainWindow();
    explicit MainWindow(QWidget *parent = 0);
private:
    CSubWidget *m_pSubWidget;
};
MainWindow::MainWindow(QWidget *parent) :
    QWidget(parent)
{
    QFile file(":/style.css");
    file.open(QIODevice::ReadOnly);
    qApp->setStyleSheet(file.readAll());
    m_pSubWidget = new CSubWidget(this);
｝

以上会发现， CSubWidget 设置的窗体样式是无效的，

查看文档会发现

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.

为CSubWidget 加上paintEvent就可以解决