mouse wheel event and QListWidget: wrong behaviour?

[d_stranz]

You should even be able to directly connect each scrollbar's valueChanged() signal to the other two scrollbar's setValue slot.

No, I think I tried this once. If you have a circular loop of connections from one list to the next and then back to the first, I am pretty sure this sets up a recursion. setValue() causes valueChanged() to be emitted.

I do not know if the sanity check in my slot is performed internally by the scroll bar, but if it is, then the recursion might not occur and you can directly connect the scrollbars' signals and slots. I will leave that as an exercise for the OP to investigate.

[anda_skoa]

setValue() causes valueChanged() to be emitted.

setValue() should only trigger valueChanged() if the value changes.
If the two scrollbars have the same range, a change of one value can be exactly mapped to the other.
The signal back would then not change anything, thus not lead to valueChanged() being emitted yet again.

Works for QSlider, which is another implementation of QAbstractSlider.
(very common to connect a slider to a spinbox and vice versa for both type and slide input)

Cheers,
_

[jho]

Thanks guys, It is working now without a hack. And so easy to implement.

[d_stranz]

setValue() should only trigger valueChanged() if the value changes.
If the two scrollbars have the same range, a change of one value can be exactly mapped to the other.
The signal back would then not change anything, thus not lead to valueChanged() being emitted yet again.

OK, then, if that's the case I can update my code to this:

MainWindow::MainWindow( QWidget * parent )
{
// ... setupUI() , etc.
 
    QScrollBar * listScroll1 = list1->verticalScrollBar();
    QScrollBar * listScroll2 = list2->verticalScrollBar();  
    QScrollBar * listScroll3 = list3->verticalScrollBar();
 
    connect( listScroll1, SIGNAL( valueChanged( int ) ), listScroll2, SLOT( setValue( int ) ) );
    connect( listScroll1, SIGNAL( valueChanged( int ) ), listScroll3, SLOT( setValue( int ) ) );
 
    connect( listScroll2, SIGNAL( valueChanged( int ) ), listScroll1, SLOT( setValue( int ) ) );
    connect( listScroll2, SIGNAL( valueChanged( int ) ), listScroll3, SLOT( setValue( int ) ) );
 
    connect( listScroll3, SIGNAL( valueChanged( int ) ), listScroll1, SLOT( setValue( int ) ) );
    connect( listScroll3, SIGNAL( valueChanged( int ) ), listScroll2, SLOT( setValue( int ) ) );
}

MainWindow::MainWindow( QWidget * parent )
{
// ... setupUI() , etc.

    QScrollBar * listScroll1 = list1->verticalScrollBar();
    QScrollBar * listScroll2 = list2->verticalScrollBar();  
    QScrollBar * listScroll3 = list3->verticalScrollBar();

    connect( listScroll1, SIGNAL( valueChanged( int ) ), listScroll2, SLOT( setValue( int ) ) );
    connect( listScroll1, SIGNAL( valueChanged( int ) ), listScroll3, SLOT( setValue( int ) ) );

    connect( listScroll2, SIGNAL( valueChanged( int ) ), listScroll1, SLOT( setValue( int ) ) );
    connect( listScroll2, SIGNAL( valueChanged( int ) ), listScroll3, SLOT( setValue( int ) ) );

    connect( listScroll3, SIGNAL( valueChanged( int ) ), listScroll1, SLOT( setValue( int ) ) );
    connect( listScroll3, SIGNAL( valueChanged( int ) ), listScroll2, SLOT( setValue( int ) ) );
}

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