在QTreeWidget中绘制直线时的相关问题
问题1 QWidget::paintEngine: Should no longer be called
错误如下：
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QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::save: Painter not active
QPainter::setPen: Painter not active
QPainter::setPen: Painter not active
QPainter::restore: Unbalanced save/restore
代码如下：
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void QRTreeWidget::paintLine()
{
QPainter painter(this);
painter.save();
QPen pen(palette().base().color());
painter.setPen(pen);
painter.drawLine(m_oldLine);
//QPen pen(Qt::green);
pen.setColor(Qt::green);
pen.setWidth(1);
painter.setPen(pen);
painter.drawLine(m_newLine);
painter.restore();
}
//错误调用位置：
void QRTreeWidget::dragMoveEvent(QDragMoveEvent* e)
{
//... ...
paintLine();
return QTreeWidget::dragMoveEvent(e);
}
//正确的调用位置
void QRTreeWidget::paintEvent(QPaintEvent* e)
{
paintLine();
return QTreeWidget::paintEvent(e);
}
Note: the only place you should create and use a painter is inside paintEvent().[只能在paintEvent中使用或者创建painter]
问题2 WA_PaintOutsidePaintEvent
错误代码如下：
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1>QRTreeWidget.cpp(9): error C2039: “WA_PaintOutsidePaintEvent”: 不是“Qt”的成员
注：关于WA_PaintOutsidePaintEvent的定义，只能在QT4的文档中找到，在QT5的文档中已经消失。
官方给出的解释如下：
Makes it possible to use QPainter to paint on the widget outside paintEvent(). This flag is not supported on Windows, Mac OS X or Embedded Linux. We recommend that you use it only when porting Qt 3 code to Qt 4.
不适合现有的系统，只适用于X11，其他系统均无效，在其他的系统中，会与到问题1类似情况！
问题3 QPainter painter(this) 绘制无效
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//需要适用一下初始化的方式 [还是viewport的问题]
QPainter painter(this->viewport());
//备注：只有在设置绘制主体为视窗，才能正确显示绘制内容！
//查看QT源码，可见：
#include "qabstractscrollarea.h" 中
QWidget *viewport() const;
QWidget *QAbstractScrollArea::viewport() const
{
Q_D(const QAbstractScrollArea);
return d->viewport;
}
