How to create a Matrix like QWidget? - qt

Question

How to create a QTableWidget with some cells filled using uniform sized widgets and the unused cells filled with the size of widgets?The resulting table should contain a row/column as blank even if no widget is present.

Answer 1

Since the QTableWidget apparently has to contain something in each cell, and the default is an editable text box, it seem the solution would be to insert a non-editable dummy item into the blank cells. Or have a custom widget which can hide its contents, which is what I've done in the example below.
You specifically asked about fixed size... there's really a number of ways to go about this, depending on the exact needs. You can set fixed sizes on the whole table by using the horizontal and vertical headers and making them non-resizable. Another way is to call QTableView::setColumnWidth() / setRowHeight() for each row/column (while adding/item or whenever).
Here's an example using the former method (setting size on headers), and two ways to determine the actual size -- either a fixed size before building the table, or using a lookup on the custom widget item to determine a size.
UPDATE: Previous version used a dummy QTableWidgetItem to fill in the blank areas, but I think this is better if one needs to use a custom widget anyway. See edit history for previous version.
// main.cpp
#include <QtWidgets>
// A custom table widget item which contains a progress bar. The bar is
// hidden if the value is set to < 0.
class ProgressBarTwItem : public QWidget, public QTableWidgetItem
{
Q_OBJECT
public:
ProgressBarTwItem(QWidget *parent = nullptr, int value = -1) :
QWidget(parent),
QTableWidgetItem(QTableWidgetItem::UserType)
{
QHBoxLayout *l = new QHBoxLayout(this);
l->setContentsMargins(0,0,0,0);
m_pb = new QProgressBar(this);
// don't let PB size dictate our size
m_pb->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
m_pb->setAlignment(Qt::AlignCenter);
m_pb->setMaximum(44);
l->addWidget(m_pb);
setValue(value);
}
QSize sizeHint() const override { return QSize(75, 25); }
public slots:
void setValue(int value = -1) const
{
m_pb->setVisible(value > -1);
if (value > -1)
m_pb->setValue(value);
}
private:
QProgressBar *m_pb;
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
a.setStyle("Fusion");
QDialog d;
d.setLayout(new QVBoxLayout);
QTableWidget *tw = new QTableWidget(5, 4, &d);
d.layout()->addWidget(tw);
// set to `true` to find the largest size from added custom widgets,
// otherwise use preset size
const bool useWidgetSize = true;
// This will be the fixed cell size, either preset or determined from custom widget.
// If looking up from widgets, this becomes the minimum size
// (eg. in case widgets didn't return valid sizes).
QSize cellSize = (useWidgetSize ? QSize(10, 10) : QSize(50, 15));
for (int r=0; r < tw->rowCount(); ++r) {
for (int c=0; c < tw->columnCount(); ++c) {
// make some widgets hidden and others display a progress value
const int val = (!((r*c) % (1+c)) ? -1 : (c+1 + r*10));
ProgressBarTwItem *item = new ProgressBarTwItem(tw, val);
tw->setCellWidget(r, c, item);
// tw->setItem(r, c, item); // needed? widget is shown anyway... docs not clear.
// Check the size.
if (useWidgetSize)
cellSize = cellSize.expandedTo(item->sizeHint());
}
}
// set fixed sizes for columns and rows on the horizontal and vertical headers
// respectively (this works even if they are hidden)
tw->horizontalHeader()->setDefaultSectionSize(cellSize.width());
tw->horizontalHeader()->setSectionResizeMode(QHeaderView::Fixed);
tw->verticalHeader()->setDefaultSectionSize(cellSize.height());
tw->verticalHeader()->setSectionResizeMode(QHeaderView::Fixed);
return d.exec();
}
#include "main.moc"