Question

代码可以工作，但是当我在执行时按下鼠标时，我收到以下警告信息：??

QPainter::begin: Widget painting can only begin as a result of a paintEvent
QPainter::setPen: Painter not active
QPainter::drawRects: Painter not active

进一步修改

#include <QTextEdit>

class QTextEditEnter : public QTextEdit
{
    Q_OBJECT
public:
    QTextEditEnter(QWidget *_parent);

protected:
    virtual void paintEvent(QPaintEvent *_event);
    void mousePressEvent(QMouseEvent *evt);
    int m_color;
    void mouseDoubleClickEvent(QMouseEvent *e);
signals:
    void signalPressEnter();
};

#include "qtexteditenter.h"
#include <qpainter.h>
#include <QMouseEvent>

QTextEditEnter::QTextEditEnter(QWidget *_parent) :
    QTextEdit(_parent)
{
    this->setFrameStyle(QFrame::Sunken);
    m_color = 0;
    setAttribute(Qt::WA_PaintOutsidePaintEvent, true);
}


void QTextEditEnter::paintEvent(QPaintEvent *_event)
{
    QPainter pnt( viewport() );
    pnt.setPen( QColor( 255, 0, 0, 0xff ));
    pnt.drawRect( 0, 0, width()-1, height()-1);
}


void QTextEditEnter::mousePressEvent(QMouseEvent *e)
{
    QPainter p(this->viewport());
    p.setPen(QColor(0,0,0,0xff));
    p.drawRect(this->viewport()->rect());
    p.begin(this);

    switch(m_color){
        case 0:
            p.setPen(Qt::red);
            break;
        case 1:
            p.setPen(Qt::green);
            break;
    }
    p.drawEllipse(e->pos(),2,2);
    p.end();
}

void QTextEditEnter::mouseDoubleClickEvent(QMouseEvent *e)
{
    m_color++;
    if (m_color > 1) m_color = 0;

}

-------------------修改----------------

void QTextEditEnter::paintEvent(QPaintEvent *_event)
{

    if(1){
        QPainter pnt( this->viewport());

        pnt.setPen( QColor( 0xff, 0, 0, 0xff ));
        pnt.drawRect( 0, 0, width()-1, height()-1);

        pnt.setPen( QColor( 0, 0xff, 0, 0xff ));
        pnt.drawRect( 10, 10, width()-20, height()-20);
    }

    if(flagModify == 1){
        QPainter p(this->viewport());

        switch(m_color){
            case 0:
                p.setPen(Qt::red);
                break;
            case 1:
                p.setPen(Qt::green);
                break;
        }

        p.begin(this);
        p.drawEllipse(x, y, 2, 2);
        p.end();

        flagModify = 0;
    }
}


void QTextEditEnter::mousePressEvent(QMouseEvent *e)
{
    x = e->pos().x();
    y = e->pos().y();

    flagModify = 1;
    this->update(this->rect());
}

Answer 1

您收到消息是因为仅在paint事件中允许绘制到窗口小部件的绘图设备。如果您在paint事件之外使用它，则无法保证它将起作用。因此，不是在mousePressEvent内绘画，而是设置状态变量（例如isPressed）并调用update，传递小部件的rect。这将触发paint事件，您可以在其中检查状态变量并相应地绘制窗口小部件。

Answer 2

在您的示例中，不调用p.begin（this）;内部

void QTextEditEnter::paintEvent(QPaintEvent *_event) {...}

如果你想摆脱警告信息。

QPainter :: begin：窗口小部件绘制只能从paintEvent开始

2 个答案: