Qt中 QPainter 刷新出现的问题

最近学习Qt 自定义绘画时碰到两个问题，问题如下：
自定义绘画图形，采用重写QPaintEvent，发现绘画不起作用；
1、Qpainter不刷新，解决方法：在触发刷新是，调用updata（）函数强行更新。

问题

其中Qpainter 的父类应该是具体绘画的widget；
对于QGraphiscView：我所碰到的问题如下：

输出：
QPainter::fillPath: Painter not active
QPainter::setPen: Painter not active
QPainter::restore: Unbalanced save/restore
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::save: Painter not active
QPainter::translate: Painter not active
QPainter::setPen: Painter not active

void ViewPager::paintEvent(QPaintEvent *e)
{

    QPainter painter(this)