我试图像这样在QLabel中绘制Qt:

paintscene.h:

class PaintScene : public QWidget
{
    Q_OBJECT
public:
    PaintScene(QWidget* parent = NULL);

    QVector<QLabel*> _layers;
    QColor _color;
    int _width;

    void mousePressEvent(QMouseEvent* event);

private slots:
    void updateWidth();
};

paintscene.cpp:
PaintScene::PaintScene(QWidget* parent) : QWidget(parent)
{
    _width = 10;
    _color = Qt::red;
    QLabel* inital = new QLabel(this);
    inital->setStyleSheet("QLabel { background-color : white; }");
    _layers.push_back(inital);

    QGridLayout* layout = new QGridLayout();
    layout->addWidget(inital, 1, 1, 1, 1);
    this->setLayout(layout);
}

void PaintScene::mousePressEvent(QMouseEvent *event)
{
    QImage tmp = _layers.back()->pixmap()->toImage();
    QPainter painter(&tmp);
    QPen paintpen(_color);
    paintpen.setWidth(_width);
    painter.setPen(paintpen);
    painter.drawPoint(event->x(), event->y());
    _layers.back()->setPixmap(QPixmap::fromImage(tmp));
}

该列表是必需的,因为我想用层(QLabel-一个单独的层)来实现工作。

但是,出现错误,程序终止。该错误发生在QImage tmp = _layers.back()->pixmap()->toImage();行上。

是什么使这种情况发生?如何解决?也许一个图层使用不同的东西,而不是QLabel

最佳答案

@Jeremy Friesner关于错误的原因是正确的,没有QPixmap,它将为null,在我的回答中,我将显示可能的解决方案

void PaintScene::mousePressEvent(QMouseEvent *event)
{
    QLabel *label = _layers.back();
    const QPixmap *pix= label->pixmap();
    QPixmap pixmap;
    if(pix)
        pixmap =  *pix;
    else{
        pixmap = QPixmap(label->size());
        pixmap.fill(Qt::transparent);
    }
    QPainter painter(&pixmap);
    QPen paintpen(_color);
    paintpen.setWidth(_width);
    painter.setPen(paintpen);
    painter.drawPoint(event->pos());
    painter.end();
    label->setPixmap(pixmap);
}

c&#43;&#43; - QLabel上的绘图点错误-LMLPHP

09-10 04:53
查看更多