QChart: Unable to get bar chart value labels to appear

MrSurly

I'm trying to simply have the numerical value of a given bar appear within the bar itself. QAbstractBarSeries provides several functions related to labels, but so far I have been unsuccessful in getting the labels to actually appear.

Here is the code in question:

QGroupBox *box = new QGroupBox("Cells", this);
auto *layout = new QBoxLayout(QBoxLayout::LeftToRight, box);

// barSeries holds the actual data
// one QBarSet (with one value)
// per cell
cellBarSeries = new QHorizontalBarSeries(this);
for (auto i = 0; i < 5; i++){
  auto barSet = new QBarSet("");
  *barSet << 3700;
  cellBarSeries->append(barSet);
}
cellBarSeries->setBarWidth(1);
// cellBarSeries->setLabelsFormat("@value");
cellBarSeries->setLabelsVisible(true);
// cellBarSeries->setLabelsPosition(QBarSeries::LabelsCenter);

// Create Chart
auto *chart = new QChart;
chart->addSeries(cellBarSeries);
chart->setAnimationOptions(QChart::SeriesAnimations);
chart->setAnimationDuration(500);
chart->legend()->setVisible(false);

// Set Margins
QMargins margins;
margins.setLeft(5);
margins.setRight(5);
margins.setTop(5);
margins.setBottom(5);
chart->setMargins(margins);

// axisX
auto axisX = new QValueAxis();
axisX->setRange(2500, 4400);
axisX->setLabelFormat("%4d");

chart->addAxis(axisX, Qt::AlignTop);
cellBarSeries->attachAxis(axisX);

// Create widget
auto *chartView = new QChartView(this);
chartView->setChart(chart);
chartView->setRenderHint(QPainter::Antialiasing, true);
layout->addWidget(chartView);

return box;

Here is the chart that it produces:

SGaist

Might be a silly question but did you set somewhere the label on the QBarSet ? It looks like what you want.

SGaist

Hi and welcome to devnet,

Do you mean something similar to that example ?

MrSurly

More like this:

Found here: https://github.com/komsit37/qchart?tab=readme-ov-file

See how each bar has a number above it?

(sorry for the late reply -- I didn't have email notifications turned on for my profile)
(also now realizing this link doesn't appear to be affiliated with QT Qchart ...)

SGaist

Might be a silly question but did you set somewhere the label on the QBarSet ? It looks like what you want.

MrSurly

@SGaist The labels come from the set values.

I've figured out what's causing the issue, but not how to solve: Adding a QValueAxis , and specifically calling series->attachAxis causes the labels to be suppressed:

Omitting attachAxis:

With attachAxis:

As you can see, doing the latter causes the bars to scale to the axis (which is my desire), but makes the labels disappear. If I had to guess, I'd say this was an intentional thing.

MrSurly

@SGaist

Okay, so the labels default to the QAbstractBarSeries::LabelsPosition::LabelsCenter, where center is defined as the middle of the bar numerically, not the middle of the bar as rendered:

Original range is 2500 to 4400.

Here's how it looks with range 1100 to 3200:

If I call series->setLabelsPosition(QAbstractBarSeries::LabelsPosition::LabelsInsideEnd), and restore the range, I get:

Long story short, the labels were there, but rendered off-screen.

SGaist

Oh ! That's a tricky one !
Glad you found out and thanks for sharing !