c++ - Qt:实现平移(拖动)的正确方法

Question

QGraphicsview 有一个方法 setDragMode(ScrollHandDrag) 来启用鼠标左键的平移。但我想在单击鼠标滚轮(中间按钮)时启用平移，并创建了以下自定义实现来平移:

//Within a custom derived class of QGraphicsView
//pan is true when wheel is clicked and false when released
//last Pos is defined somewhere else in the class

void GridView::mouseMoveEvent(QMouseEvent *event){
     if(pan){
         QPointF currentPos = event->pos();
         QPointF relPos = currentPos - lastPos;
         lastPos = currentPos;

         //this is what creates the panning effect
         translate(relPos.x(), relPos.y());
     }
     QGraphicsView::mouseMoveEvent(event);
}

这在大多数情况下工作正常。但是，例如，如果我将单位矩阵缩放 1,000,000，此方法将失败并停止平移(就好像 View 卡住了一样)。当我使用 setDragMode()

时不会出现这个问题

setDragMode() 的正确自定义实现是什么，以便通过滚轮点击启用它？

Answer 1

这对我有用...它欺骗 Qt 以为用户按下鼠标左键，而实际上他按下的是鼠标左键。

void GridView :: mousePressEvent(QMouseEvent * e)
{
   if (e->button() == MidButton)
   {
      QMouseEvent fake(e->type(), e->pos(), LeftButton, LeftButton, e->modifiers());
      QGraphicsView::mousePressEvent(&fake);
   }
   else QGraphicsView::mousePressEvent(e);
}

void GridView :: mouseReleaseEvent(QMouseEvent * e)
{
   if (e->button() == MidButton)
   {
      QMouseEvent fake(e->type(), e->pos(), LeftButton, LeftButton, e->modifiers());
      QGraphicsView::mouseReleaseEvent(&fake);
   }
   else QGraphicsView::mouseReleaseEvent(e);
}