C++ & Qt

28 March 2026 20:00

Welcome to the group, @Gencemiri! :-)

Wanna share your story of how you started with Qt, QML or C++? Maybe some nice feature that made you stick with it.
Rules are set on the description of the group. :)

C++ & Qt

25 March 2026 10:26

maybe i am missing something

C++ & Qt

25 March 2026 10:22

and this works with 10k messages well

C++ & Qt

25 March 2026 10:20

and damn right it is faster

C++ & Qt

25 March 2026 09:57

perhaps it doesn't have to be perfect either? Skipping some lines when resizing isn't that much of a problem perhaps?

C++ & Qt

25 March 2026 09:55

also wondering what will happen if i will just be getting element in the vierwport and calling the resizeRowToContents

C++ & Qt

25 March 2026 09:53

or only on visible elements

C++ & Qt

25 March 2026 09:43

resizeToContents on first 3 columns also make gui thread go up to 100% but without visible lag. this could be made fixed size thats all

C++ & Qt

25 March 2026 09:40

so if i set all resize policies to fixed without word wrap and the 4th column to stretch(cant see full mesage) or interactive(this could work but word wrap + stretch would be beter), i get decent performance

if on to of previous i do word wrap, nothing is changing because the row height is fixed, but if i enable resizeToContents on the vertical header i get huuuge performance penalty

C++ & Qt

25 March 2026 09:26

god damn there is no valgrind on mac arm yet, constant pain in the butt, i have to use pc for this purposes

C++ & Qt

25 March 2026 09:04

so this behave same on my air m2. scroll is takin 2-3% of cpu is short bursts (idk seems ok), resize with mouse eats up entire gui thread/core to 100%

C++ & Qt

25 March 2026 00:25

Also the below calls are very expensive and should be aboided if used.

resizeColumnsToContents() / resizeRowsToContents()

C++ & Qt

24 March 2026 21:20

I have done similar things with tables in qml. Apparently qml uses single point precision for row offsets, so if the number of rows are big enough the layout gets weird (even if the performance is good)

C++ & Qt

24 March 2026 21:13

You can also do that in the parent widget by using only x rows in the listview.

C++ & Qt

24 March 2026 15:47

Uniform row heights is also good, but I suppose you want it to look as in the image above

C++ & Qt

25 March 2026 11:46

I think the main thing is to not let it recalculate everything at 60 Hz (or worse)

C++ & Qt

25 March 2026 10:26

i would like to hear some suggestions bout the "not letting the table view do something by itself on resize for all rows/columns"

C++ & Qt

25 March 2026 10:22

but yea the scroll bar does not feel alright

C++ & Qt

25 March 2026 10:19

so i managed to make this

log_view::log_view(log_model* lm)
    : QTableView(nullptr) {
 setModel(lm);
 setAlternatingRowColors(true);
 setSelectionMode(QAbstractItemView::SingleSelection);
 setSelectionBehavior(QAbstractItemView::SelectRows);
 setWordWrap(true);

 verticalHeader()->setSectionResizeMode(QHeaderView::Fixed);
 verticalHeader()->setDefaultSectionSize(24);

 auto header = horizontalHeader();
 // i gave up on dynamic columns, just eyeballed the default size and let the
 // user change it god damn
 header->setSectionResizeMode(0, QHeaderView::Interactive);
 header->resizeSection(0, 140);
 header->setSectionResizeMode(1, QHeaderView::Interactive);
 header->resizeSection(1, 80);
 header->setSectionResizeMode(2, QHeaderView::Interactive);
 header->resizeSection(2, 73);
 header->setSectionResizeMode(3, QHeaderView::Stretch);

 connect(
  header, &QHeaderView::sectionResized,
  this, &log_view::on_section_resized
 );

 connect(
  verticalScrollBar(), &QScrollBar::valueChanged,
  this, &log_view::schedule_visible_row_resize
 );

 connect(
  model(), &QAbstractItemModel::dataChanged, this,
  [this](const QModelIndex& topLeft, const QModelIndex& bottomRight) {
   if (topLeft.column() == 3) {
    for (int r = topLeft.row(); r <= bottomRight.row(); ++r)
    if (visualRect(model()->index(r, 0)).intersects(viewport()->rect()))
     resizeRowToContents(r);
   }
  }
 );

 QMetaObject::invokeMethod(this, &log_view::schedule_visible_row_resize, Qt::QueuedConnection);
}

void log_view::on_section_resized(int logicalIndex, int oldSize, int newSize) {
 if (logicalIndex == 3)
  schedule_visible_row_resize();
}

void log_view::schedule_visible_row_resize() {
 QMetaObject::invokeMethod(
  this, &log_view::update_visible_row_heights,
  Qt::QueuedConnection
 );
}

void log_view::update_visible_row_heights() {
 if (!model() || model()->rowCount() == 0)
  return;

 setUpdatesEnabled(false);

 const int first = rowAt(0);
 if (first < 0) {
  setUpdatesEnabled(true);
  return;
 }

 int last = rowAt(viewport()->height() - 1);
 if (last < 0)
  last = model()->rowCount() - 1;

 for (int row = first; row <= last; ++row)
  resizeRowToContents(row);

 setUpdatesEnabled(true);
}

void log_view::resizeEvent(QResizeEvent* ev) {
 setUpdatesEnabled(false); // importand to not let the table view do nothin by itlself
 QTableView::resizeEvent(ev);
 setUpdatesEnabled(true);
 schedule_visible_row_resize();
}

Qt’s standard “do it once, later” pattern

When the current event loop finishes processing all the resize/scroll/paint events that are already queued, then run this once

C++ & Qt

25 March 2026 09:55

but the scrollbar wont cbe in correct scale

C++ & Qt

25 March 2026 09:54

it has to look at all elements above at least (and perhaps the rest of them to get the scrollbar size right)

C++ & Qt

25 March 2026 09:52

With dynamic row height it has to do that i suppose, but perhaps it could happen less often

C++ & Qt

25 March 2026 09:41

i wonder as if the widget tries to recalculate all the heights, maybe this could be optimized to only update visible elements somehow

C++ & Qt

25 March 2026 09:27

not as bad as this though

C++ & Qt

25 March 2026 09:13

this defenitetly helps with performance with 200 elements. but with 10k it is not enough

C++ & Qt

25 March 2026 07:09

@Dolfost i tried this and it doesn't feel that slow on my machine:

QStandardItemModel* lm = new QStandardItemModel();
lm->setColumnCount(4);

for(int i = 0; i < 2000; ++i)
{
QList<QStandardItem*> row;

row << new QStandardItem(QString::number(i)) << new QStandardItem("A") << new QStandardItem("B");
if(i % 20 == 0)
row << new QStandardItem("CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC ");
else
row << new QStandardItem("C");

lm->appendRow(row);
}

ui->log_view->setModel(lm);
ui->log_view->setAlternatingRowColors(true);
ui->log_view->setSelectionMode(QAbstractItemView::SelectionMode::SingleSelection);
ui->log_view->setSelectionBehavior(QAbstractItemView::SelectionBehavior::SelectRows);
ui->log_view->verticalHeader()->setSectionResizeMode(QHeaderView::ResizeMode::ResizeToContents);

auto header = ui->log_view->horizontalHeader();

header->setSectionResizeMode(0, QHeaderView::ResizeMode::ResizeToContents);
header->setSectionResizeMode(1, QHeaderView::ResizeMode::ResizeToContents);
header->setSectionResizeMode(2, QHeaderView::ResizeMode::ResizeToContents);

header->setSectionResizeMode(3, QHeaderView::ResizeMode::Stretch);
ui->log_view->setWordWrap(true);
connect(header, &QHeaderView::sectionResized, this,
[this](int logicalIndex, int /*oldSize*/, int /*newSize*/) {
if (logicalIndex == 3)
ui->log_view->resizeRowsToContents();
}
);

C++ & Qt

25 March 2026 00:18

It's been quite a long since I used widgets. I can suggest the below solution.

Try disable updates while resizing.

Qt repaints continuously during a resize event. You can suppress this.

Override resizeEvent.

void MyWidget::resizeEvent(QResizeEvent *event)
{
tableWidget->setUpdatesEnabled(false);
QWidget::resizeEvent(event);
tableWidget->setUpdatesEnabled(true);
}

C++ & Qt

24 March 2026 21:15

In one of my projects, I have a thumbnail view that with about 100k pictures. Performance was really bad - in the end, I just implemented the paintEvent() myself. It's really nice now.

C++ & Qt

24 March 2026 21:13

I'd probably subclass the list widget and only render the visible portion of the list.

C++ & Qt

24 March 2026 15:08

200 rows should work even without models I think