c++ - Qt橡皮筋没有被绘制

Question

我正在尝试实现橡皮筋。这是我的代码。

void TOTMain::mousePressEvent(QMouseEvent * event)
{
    QPoint origin = event->pos();
    _selectionSquare = new QRubberBand(QRubberBand::Rectangle, this);
    _selectionSquare->setGeometry(QRect(origin, QSize()));
    _selectionSquare->raise();
    _selectionSquare->show();
}

void TOTMain::mouseMoveEvent(QMouseEvent *event)
{
    QPoint origin = event->pos();
    _selectionSquare->setGeometry(QRect(origin, event->pos()).normalized());
}

void TOTMain::mouseReleaseEvent(QMouseEvent *event)
{
    _selectionSquare->hide();
    // determine selection, for example using QRect::intersects()
    // and QRect::contains().
}

问题是未绘制带。我确认它正在构建并通过拖动持续存在，但没有渲染。

任何想法表示赞赏。

Answer 1

看看您的mouseMoveEvent 实现...

void TOTMain::mouseMoveEvent(QMouseEvent *event)
{
    QPoint origin = event->pos();
    _selectionSquare->setGeometry(QRect(origin, event->pos()).normalized());
}

您正在将橡皮筋的几何形状设置为 QRect(origin, event->pos())，但是您之前已经设置了 origin = event->pos() 所以矩形的左上角和右下角是相同的。

使 origin 成为您类的成员变量变量(未测试)...

class TOTMain: public QWidget {
public:
protected:
    virtual void mousePressEvent (QMouseEvent *event) override
    {
        _origin = event->pos();
        _selectionSquare = new QRubberBand(QRubberBand::Rectangle, this);
        _selectionSquare->setGeometry(QRect(_origin, QSize()));
        _selectionSquare->raise();
        _selectionSquare->setStyleSheet("{ background-color : red; }");
        _selectionSquare->show();
    }
    virtual void mouseMoveEvent (QMouseEvent *event) override
    {
        _selectionSquare->setGeometry(QRect(_origin, event->pos()).normalized());
    }
    virtual void mouseReleaseEvent (QMouseEvent *event) override
    {
        _selectionSquare->hide();
        // determine selection, for example using QRect::intersects()
        // and QRect::contains().
    }
private:
    QPoint       _origin;
    QRubberBand *_selectionSquare = nullptr;
};