QListView touch scroll and item selection, how to differentiale scroll and click ?

[remy_david]

Hello,

I try to make a scrollable list with selectable items. The user should be able to scroll the list with a touch movment (up/down) and select a list item with a tap (i.e. just like the lists in iOS, Android and any other mobile platforms out there).

I made the list scrollable by touch with this trick that I found here :

void MyListView::mouseMoveEvent ( QMouseEvent * event )
{
    this->QListView::mouseMoveEvent(event);
    QScrollBar *scroll =  verticalScrollBar();
    scroll->setValue(scroll->value() - event->y() + y0);
    y0 = event->y();
}

void MyListView::mousePressEvent ( QMouseEvent * event )
{
    this->QListView::mousePressEvent(event);
    y0 = event->y();
}

void MyListView::mouseReleaseEvent(QMouseEvent * event)
{
    this->QListView::mouseReleaseEvent(event);
    y0 = -1;
}

However I don't manage to get the proper event for item selection.

QListView has the following signals:

void	activated ( const QModelIndex & index )
void	clicked ( const QModelIndex & index )
void	pressed ( const QModelIndex & index )

But they all fire when the user drag the list to scroll. IMHO clicked/pressed/activated should only occur with a tap, not with a drag. Is this a bug or a feature? How do you detect a tap ?

As a more general comment, I seems Qt do not support touch events or is it me ? (I am not even talking about multi touch)

[divanov]

However I don't manage to get the proper event for item selection.

Could you please clarify what you get instead?

[remy_david]

I get item selection events (i.e. clicked/pressed/activated) both when selecting an item and when draging (i.e. scrolling) the list.
So I cannot differentiate between click (i.e. item selection) and drag (i.e. scrolling the list).
I want to receive a selection event ONLY when selecting an item.

[remy_david]

I try to implement the solution used by QsKineticScroller .
But instead of using an event filter, I want to include touch management directly inside my QListView subclass. So I moved the code from the event filter directly into my overloaded event functions.
Kinetic scrolling is working but I have a problem for detecting the click :

void MyListView::mouseReleaseEvent(QMouseEvent * mouseEvent)
{    
    isPressed = false;
    // Looks like the user wanted a single click. Simulate the click,
    // as the events were already consumed
    if( !isMoving )
    {
       QMouseEvent* mousePress = new QMouseEvent(QEvent::MouseButtonPress,
          lastPressPoint, Qt::LeftButton, Qt::LeftButton, Qt::NoModifier);
       QMouseEvent* mouseRelease = new QMouseEvent(QEvent::MouseButtonRelease,
          lastPressPoint, Qt::LeftButton, Qt::LeftButton, Qt::NoModifier);

       ignoredMouseActions = 2;
       QApplication::postEvent(this, mousePress); 
       QApplication::postEvent(this, mouseRelease);
   }
}

It seems those lines :

QApplication::postEvent(this, mousePress); 
QApplication::postEvent(this, mouseRelease);

have no effect when called from mouseReleaseEvent. If called from the event filter it's working.
MyListView (aka this) never receive mousePress / mouseRelease events (i.e. mouseReleaseEvent and mousePressEvent are never called). Do you have an idea why ?

[divanov]

Did you try to use kinetic scroller backported to Qt 4.6-4.7 from 4.8?
http://qt.gitorious.org/qt-labs/kine...olution/README
Note: it's LGPL, not BSD.

[remy_david]

Thanks, I finally found a solution and the QsKineticScroller from the wiki is under BSD which fits my needs better.
So I replaced:

void MyListView::mouseReleaseEvent(QMouseEvent * mouseEvent)
{    
    isPressed = false;
    if( !isMoving )
    {
       QMouseEvent* mousePress = new QMouseEvent(QEvent::MouseButtonPress,
          lastPressPoint, Qt::LeftButton, Qt::LeftButton, Qt::NoModifier);
       QMouseEvent* mouseRelease = new QMouseEvent(QEvent::MouseButtonRelease,
          lastPressPoint, Qt::LeftButton, Qt::LeftButton, Qt::NoModifier);

       ignoredMouseActions = 2;
       QApplication::postEvent(this, mousePress); 
       QApplication::postEvent(this, mouseRelease);
   }
}

by

void MyListView::mouseReleaseEvent(QMouseEvent * mouseEvent)
{    
    isPressed = false;
    if( !isMoving )
        emit(selected(indexAt(lastPressPoint)));
}

So instead of simulating a mouse click when the algorythm detect that the user has clicked, I emit a new signal called selected.

I would be curious to know why postEvent was not working to simulate the mouse click in this case though.