在默认的QWidget上绘制

Question

我可以在按下按钮时在Qt中绘制默认的QWidget，或者我总是创建QWidget的子类并使用其paintEvent()方法?

Answer 1

不讨论这种设计背后的意图，允许在没有子类的情况下对所有小部件进行共同绘制，我们可以这样做:

class MyEventFilter : public QObject
{
public:
    MyEventFilter(QObject *parent = 0) : QObject(parent)
    {}
    bool eventFilter(QObject *obj, QEvent *e)
    {
        if (e->type() == QEvent::Paint)
        {
            QPaintEvent *ptrPaintEvent = static_cast<QPaintEvent *>(e);
            // depending on whether or not you want to have a default handling for this:
            // QObject::eventFilter(obj, e);
            // OR better to apply to specific event handler, pass widget as parent for this filter object for that 
            // static_cast<QWidget*>(parent())->paintEvent(ptrPaintEvent);
            // now do same thing as you would in paintEvent()
            return true;
        }
        // standard event processing
        return QObject::eventFilter(obj, e);
    }
};
// and attach it to just any widget
myWidget->installEventFilter(new MyEventFilter(myWidget));