How to refresh data on horizontal header of QTableWidget?

tovax

@mrjj
Hi,
According to your suggestion, I blocked "headerDataChanged" signal, and add this public function to Model Class:

void MotionSheetTableModel::HeaderChange(int32_t first, int32_t last)
{
    emit headerDataChanged(Qt::Horizontal, first, last);
}

But no significant improvement in test results.
Is my understanding right, please?

Best Regards!

mrjj

@tovax
If by blocked you mean
// emit headerDataChanged(orientation, section, section);
and call your new function (HeaderChange) after the loop then we are on same page.

Ok so that didnt speed it up. :(
Im not sure how altering the list
posCmdList[section] = QString::number(value.value<double>(), 'f', 2);
would be slow.

I think i would insert some timing functions
(https://doc.qt.io/qt-5/qelapsedtimer.html is handy for that)
and see where the time is spend.
Now we know its not from pure updates so we need to find the spot where the time is used.

Also 10 times pr second does not sound that massive but I would try other values to see
where the sweet spot it.

tovax

@mrjj
I add this debug code:

bool MotionSheetTableModel::setHeaderData(int32_t section, Qt::Orientation orientation, const QVariant &value, int32_t role)
{
    Q_UNUSED(orientation);
    if (role == Qt::DisplayRole) {
        QElapsedTimer timer;
        timer.start();
        posCmdList[section] = QString::number(value.value<double>(), 'f', 2);
        qDebug() << "MotionSheetTableModel::setHeaderData" << timer.nsecsElapsed();
        // emit headerDataChanged(orientation, section, section);
    }

    return true;
}

Result as follow:

MotionSheetTableModel::setHeaderData 28158
MotionSheetTableModel::setHeaderData 27646
MotionSheetTableModel::setHeaderData 28158
MotionSheetTableModel::setHeaderData 27646
MotionSheetTableModel::setHeaderData 28158
MotionSheetTableModel::setHeaderData 28670
MotionSheetTableModel::setHeaderData 53244
MotionSheetTableModel::setHeaderData 31741
MotionSheetTableModel::setHeaderData 28158
MotionSheetTableModel::setHeaderData 28158
MotionSheetTableModel::setHeaderData 28670
MotionSheetTableModel::setHeaderData 28158
MotionSheetTableModel::setHeaderData 28158
MotionSheetTableModel::setHeaderData 27646
MotionSheetTableModel::setHeaderData 28158
MotionSheetTableModel::setHeaderData 28158
MotionSheetTableModel::setHeaderData 28670
MotionSheetTableModel::setHeaderData 27646
MotionSheetTableModel::setHeaderData 28670
MotionSheetTableModel::setHeaderData 28670

Nanoseconds, It looks fast enough.

Best Regards!

mrjj

Hi
Yes it does indeed look ok fast.
I would then disable the new function to check if app still feels
laggy and its related to View redrawing.
( not send the headerDataChanged signal)

i know you wont see the updates then but its a ok test to see if you are stressing
the event loop anyways.

If app still laggy with View not repainting it means the event loop is stressed.

tovax

@mrjj
Hi,
When not send the headerDataChanged signal, the app run smoothly.
By the way, if the data display in the table cell, the app run smoothly too.

tovax

@mrjj
Here is the system time in relevent function:

onPosCmd - start "22:06:33:908"
setHeaderData 0 "22:06:33:908"
setHeaderData 1 "22:06:33:908"
setHeaderData 2 "22:06:33:909"
setHeaderData 3 "22:06:33:909"
setHeaderData 4 "22:06:33:909"
setHeaderData 5 "22:06:33:910"
setHeaderData 6 "22:06:33:910"
setHeaderData 7 "22:06:33:910"
setHeaderData 8 "22:06:33:911"
setHeaderData 9 "22:06:33:911"
setHeaderData 10 "22:06:33:911"
setHeaderData 11 "22:06:33:911"
setHeaderData 12 "22:06:33:912"
setHeaderData 13 "22:06:33:912"
setHeaderData 14 "22:06:33:912"
setHeaderData 15 "22:06:33:913"
onPosCmd - end "22:06:33:913"
headerData 0 "22:06:33:953"
headerData 1 "22:06:33:954"
headerData 8 "22:06:33:956"
headerData 9 "22:06:33:957"
headerData 10 "22:06:33:958"
headerData 11 "22:06:33:959"
headerData 12 "22:06:33:960"
headerData 13 "22:06:33:961"
headerData 14 "22:06:33:962"
headerData 15 "22:06:33:963"
headerData 0 "22:06:33:976"
headerData 1 "22:06:33:978"
headerData 8 "22:06:33:980"
headerData 9 "22:06:33:982"
headerData 10 "22:06:33:984"
headerData 11 "22:06:33:985"
headerData 12 "22:06:33:987"
headerData 13 "22:06:33:989"
headerData 14 "22:06:33:990"
headerData 15 "22:06:33:992"

It doesn't seem to waste much time on signaling.

Christian Ehrlicher

What resize mode do you use? And can you provide a small test example so we can run it e.g. with callgrind to see where the time is spend.

tovax

@mrjj
From "setHeaderData" to "headerData" waste 40ms. Will this have an impact, please?

tovax

@Christian-Ehrlicher
Hi,
The resize mode is QHeaderView::Stretch, this is the config of tableView:

    tableView = new QTableView(this);
    tableView->setModel(tableModel);

    tableView->setFrameShape(QFrame::NoFrame);

    tableView->horizontalHeader()->setVisible(true); 
    tableView->horizontalHeader()->setSectionResizeMode(QHeaderView::Stretch);

    tableView->verticalHeader()->setVisible(true); 
    tableView->verticalHeader()->setSectionResizeMode(QHeaderView::Stretch);

    tableView->setSelectionBehavior(QAbstractItemView::SelectItems);
    tableView->setSelectionMode(QAbstractItemView::ExtendedSelection);
    tableView->setAlternatingRowColors(true);

Christian Ehrlicher

@tovax said in How to refresh data on horizontal header of QTableWidget?:

The resize mode is QHeaderView::Stretch

Ok, this is at least not a problem for the update. So please provide a small testcase.

tovax

This post is deleted!

tovax

@Christian-Ehrlicher
Here is the github link:
TableView
Best Regards!

Christian Ehrlicher

@tovax: I'll give it a try today, thx

Christian Ehrlicher

Looks like the culprit is that a header data change triggers a complete repaint through QAbstractItemView::updateGeometries() which is very expensive. It doesn't matter if you call headerDataChanged() once per section or completely - it's a delayed trigger.

tovax

@Christian-Ehrlicher
Hi,
In other words, can't I update the data on the horizontal header, please?
Best Regards!

mrjj

@tovax
Hi
Nope, not as fast as you wish.
On my (albeit old) gamer pc, it uses 28% CPU to refresh it.
So for less powerful system, you will have to find another way to do the same
than using the headers. Its too expensive to be used in this way.
( even 'just' 10 times pr second )

So basically its not a supported use case with Qt to have high-speed header refresh. That said you might be able to fix it with a custom HeaderView
but if there is enough virtual function to override this behavior, i cannot say currently.

Christian Ehrlicher

Or, as we said already more times - don't try to update at 100Hz - noone can ever read this...

tovax

OK, Thanks for both of you! I'll think about other ways.
Best Regards!

tovax

Solved:

Derived from QAbstractTableModel + QTableView
Create two QTableView, one for cell's data, another for header data.
Frozen the first row of the QTableView used for header data, and refresh data in it (100Hz).
(Refer to official demo: Frozen Column Example)