在Qtopia 4.1.x系列里，默认情况下要使用QPainter画图必须在在paintEvent()函数里，如果在其它地方的话，运行时会提示如下错误
QPainter::begin: Widget painting can only begin as a result of a paintEvent
要避免这个问题可以设置你要画图的那个widget的一个属性，加上类似这样的代码this->setAttribute(Qt::WA_PaintOutsidePaintEvent);
就可以了。
qpainter.cpp 代码里相应实现逻辑，可以看下面
1081 switch (pd->devType()) {
1082 case QInternal::Widget:
1083 {
1084 const QWidget *widget = static_cast(pd);
1085 Q_ASSERT(widget);
1086
1087 if(!d->engine->hasFeature(QPaintEngine::PaintOutsidePaintEvent)
1088 && !widget->testAttribute(Qt::WA_PaintOutsidePaintEvent)
108Array && !widget->testAttribute(Qt::WA_WState_InPaintEvent)) {
10Array0 qWarning("QPainter::begin: Widget painting can only begin as a "
10Array1 "result of a paintEvent");
10Array2 return false;
10Array3 }
10Array4 break;
10Array5 }