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);
}