Cannot set the backgroud color of the HorizontalHeaderItem of QTableWidget

[tester]

The setBackground() function CANNOT set the item's background brush to the specified brush on the HorizontalHeaderItem of QTableWidget.

setForeground() function is OK.

Why?

Do you have any advices ? Thanks.

#include <QApplication>

#include <QTableWidget>
#include <QTableWidgetItem>

#include <QHeaderView>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QTableWidget *table = new QTableWidget;

    table->setColumnCount(4);
    table->setRowCount(2);


    QStringList header;
    header<<"1"<<"2"<<"3"<<"4";
    table->setHorizontalHeaderLabels(header);

    for(int i=0; i<4; i++)
    {

        QString strtmp;

        QTableWidgetItem *columnHeaderItem = table->horizontalHeaderItem(i);
        columnHeaderItem->setBackground(QBrush(QColor(0,255,0)));///////no effect,why？？？
        columnHeaderItem->setForeground(QBrush(QColor(0,0,255)));///////OK!
        columnHeaderItem->setText(strtmp.setNum(i));

        table->setHorizontalHeaderItem(i,columnHeaderItem);


        QTableWidgetItem *columnHeaderItem1 = new QTableWidgetItem;
        columnHeaderItem1->setBackground(QBrush(QColor(0,255,0)));/////OK!
        columnHeaderItem1->setForeground(QBrush(QColor(255,0,0)));
        columnHeaderItem1->setText(strtmp.setNum(i+4));

        table->setItem(0,i,columnHeaderItem1);


        QTableWidgetItem *columnHeaderItem2 = new QTableWidgetItem;
        columnHeaderItem2->setBackground(QBrush(QColor(255,255,0)));///////////////OK!
        columnHeaderItem2->setForeground(QBrush(QColor(0,0,255)));
        columnHeaderItem2->setText(strtmp.setNum(i+8));

        table->setItem(1,i,columnHeaderItem2);

    }

    table->show();

    return a.exec();
}

[VRonin]

try replacing

QTableWidgetItem *columnHeaderItem = table->horizontalHeaderItem(i);
 columnHeaderItem->setBackground(QBrush(QColor(0,255,0)));

with

QTableWidgetItem *columnHeaderItem = table->horizontalHeaderItem(i);
Q_ASSERT(columnHeaderItem);
 columnHeaderItem->setData(Qt::BackgroundRole,QBrush(QColor(0,255,0)));

[mrjj]

@VRonin said in Cannot set the backgroud color of the HorizontalHeaderItem of QTableWidget:

Q_ASSERT(columnHeaderItem);

Good idea, but It is non null.
The columnHeaderItem->setBackground(QBrush(QColor(0, 255, 0)));
does seems to have no effect :)
When used in header.

[VRonin]

In this case you probably want to set the stylesheet of the headerview or reimplement its paintEvent

[mrjj]

@VRonin
Guess so.
But is it not strange the items can change background color when used in the
data cells but not in the cells in HeaderView ?
I guess the Qt::BackgroundColorRole is used differently.

[VRonin]

@mrjj said in Cannot set the backgroud color of the HorizontalHeaderItem of QTableWidget:

But is it not strange the items can change background color when used in the data cells but not in the cells in HeaderView ?

It is strange indeed, I checked the sources and the background is definitely used in QHeaderView::paintSection

QVariant backgroundBrush = d->model->headerData(logicalIndex, d->orientation,
                                                    Qt::BackgroundRole);
    if (backgroundBrush.canConvert<QBrush>()) {
        opt.palette.setBrush(QPalette::Button, qvariant_cast<QBrush>(backgroundBrush));
        opt.palette.setBrush(QPalette::Window, qvariant_cast<QBrush>(backgroundBrush));
        painter->setBrushOrigin(opt.rect.topLeft());
    }

[mrjj]

@VRonin
Hmm Good info. It should work then.
Thank you for the code check. ! :)

[SGaist]

@VRonin @mrjj, unless I'm mistaken, the style might be ultimately ignoring it.

[VRonin]

@SGaist said in Cannot set the backgroud color of the HorizontalHeaderItem of QTableWidget:

unless I'm mistaken

You never are

from QWindowsStyle::drawControl

case CE_HeaderSection: {
        QBrush fill;
        if (opt->state & State_On)
            fill = QBrush(opt->palette.light().color(), Qt::Dense4Pattern);
        else
            fill = opt->palette.brush(QPalette::Button);

so, at least in windows, it's ignored

[mrjj]

@VRonin
Super.
So even Header accepts an QTableWidgetItem,
the setBackground Brush will not be used.
Thank you for digging :)