How QTableView or QListView is scrolling with hand drag? - c++

Question

in QGraphicview,
if we set it with : ui->graphicsView->setDragMode(QGraphicsView::ScrollHandDrag);
this code make graphicsview can scroll items with mouse pressed and drag.
How can we make QListView or QTableView as the QGraphicsView?

Answer 1

You will need to subclass these widgets and reimplement QWidget::mousePressEvent, QWidget::mousMoveEvent and QWidget::mouseReleaseEvent. However you will have to be careful because you may be interfering with actions that are mapped to these by default implementations (e.g. selecting) so it would need to be tweaked a bit. For example (assumed subclass of QListView):
void MyListView::mousePressEvent(QMouseEvent *event)
{
if(event->button() == Qt::RightButton) //lets map scrolling to right button
m_ScrollStart = event->pos(); //QPoint member, indicates the start of the scroll
else
QListView::mousePressEvent(event);
}
and then
void MyListView::mouseMoveEvent(QMouseEvent *event)
{
if(!m_ScrollStart.isNull()) //if the scroll was started
{
bool direction = (m_ScrollStart.y() < event->pos().y()); //determine direction, true is up (start is below current), false is down (start is above current)
int singleStep = (direction ? 10 : -10); //fill in the desired value
verticalScrollBar()->setValue(verticalScrollBar()->value() + singleStep);
//scroll by the certain amount in determined direction,
//you decide how much will be a single step... test and see what you like
}
QListView::mouseMoveEvent(event);
}
and finally
void MyListView::mouseReleaseEvent(QMouseEvent *event)
{
m_ScrollStart = QPoint(); //resets the scroll drag
QListView::mouseReleaseEvent(event);
}

Answer 2

like Resurrection did mention
You will need to subclass these widgets and reimplement QWidget::mousePressEvent, QWidget::mousMoveEvent and QWidget::mouseReleaseEvent
but below code is more preferred by us:
class MyListView : public QListView
{
typedef QListView super;
public:
explicit MyListView(QWidget *parent = 0);
protected:
// QWidget interface
void mousePressEvent(QMouseEvent *) Q_DECL_OVERRIDE;
void mouseReleaseEvent(QMouseEvent *) Q_DECL_OVERRIDE;
void mouseMoveEvent(QMouseEvent *) Q_DECL_OVERRIDE;
private:
enum DragState {
DragStopped,
DragStarted,
Dragged
};
quint8 m_dragState;
int m_dragStartPos;
};
MyListView::MyListView(QWidget *parent)
: super(parent)
, m_dragState(DragStopped)
, m_dragStartPos(-1)
{
}
void MyListView::mousePressEvent(QMouseEvent *event)
{
if(event->button() == Qt::LeftButton) {
m_dragState = DragStarted;
m_dragStartPos = event->pos().y();
} else
super::mousePressEvent(event);
}
void MyListView::mouseReleaseEvent(QMouseEvent *event)
{
if(m_dragState) {
m_dragState = DragStopped;
m_dragStartPos = -1;
return;
}
super::mouseReleaseEvent(event);
}
void MyListView::mouseMoveEvent(QMouseEvent *event)
{
if(m_dragState != DragStopped) {
const int itemSize = sizeHintForRow(0) / 2;
const int distance = qAbs(m_dragStartPos - event->pos().y());
if(distance > 10)
m_dragState = Dragged;
if(distance > itemSize) {
QScrollBar *scrollBar = this->verticalScrollBar();
int stepCount = (distance/itemSize);
if(m_dragStartPos < event->pos().y())
stepCount = -stepCount; //scrolling up
scrollBar->setValue(scrollBar->value() + (stepCount * scrollBar->singleStep()));
m_dragStartPos = event->y();
}
return;
}
super::mouseMoveEvent(event);
}