How can I center QCheckBox in QTableView?

CuriousPan

I have 2 table views in my application. I'd like to have centered checkboxes as delegates for specific columns. One table should have delegate editable and another not.
Making a research, I leared that I have to implement my own delegate for it. Googling led me to this pretty old but useful link: https://www.qtcentre.org/threads/19157-QTableView-checkbox-center-with-stylesheet.
Unfortunately, after creating and setting delegates, everything is displayed as 'checked' and nothing has checking possibility. Also, I don't really understand how to use it. Thank you.

Christian Ehrlicher

You should follow this example: https://wiki.qt.io/Center_a_QCheckBox_or_Decoration_in_an_Itemview

raven-worx

@CuriousPan
yep, definitely follow the example provided by @Christian-Ehrlicher.
its always better to draw stuff rather than instantiate widgets for such purposes!

eyllanesc

@CuriousPan Another solution is use QProxyStyle, see https://stackoverflow.com/questions/60947269/pyqt5-qtablewidget-item-alignment/60954464#60954464:

class CheckBoxStyle: public QProxyStyle{
public:
    using QProxyStyle::QProxyStyle;
    QRect subElementRect(QStyle::SubElement element, const QStyleOption *option, const QWidget *widget=nullptr) const{
        QRect r = QProxyStyle::subElementRect(element, option, widget);
        if(element == QStyle::SE_ItemViewItemCheckIndicator){
            r.moveCenter(option->rect.center());
        }
        return r;
    }
}

CheckBoxStyle* checkbox_style = new CheckBoxStyle(tableview->style());
tableview->setStyle(checkbox_style);

raven-worx

@eyllanesc
this moves every single checkbox in the table to the center...

CuriousPan

@Christian-Ehrlicher, hey, this is a really nice example, but I don't understand what 'role' should I use in the model to center the checkbox, because now it's in the left top corner.

JonB

@CuriousPan
The code at @Christian-Ehrlicher's https://wiki.qt.io/Center_a_QCheckBox_or_Decoration_in_an_Itemview tells you what role it is using

As alignment indicator the Qt::TextAlignmentRole is 'misused' since no text is drawn for the cell.

and you can see it in the code you are copying:

opt.rect = QStyle::alignedRect(opt.direction, index.data(Qt::TextAlignmentRole).value<Qt::Alignment>(), rect.size(), opt.rect);

Or use your own role if you don't want to use that.

CuriousPan

@JonB, yeees, I understood this and I was using Qt::TextAlignmentRole and returning Qt::AlignCenter, but for some reason it's not aligned :(

JonB

@CuriousPan
I do not know about the behaviour of the delegate. But if you want to know to know whether it is being "triggered" and recognises the role in question put in a qDebug() statement (in the delegate) to find out.

CuriousPan

This post is deleted!

CuriousPan

@JonB, yes, it's defenitely triggered.

JonB

@CuriousPan
Find all your occurrences of

QStyle::alignedRect(opt.direction, index.data(Qt::TextAlignmentRole).value<Qt::Alignment>(), rect.size(), opt.rect)

and qDebug() << index.data(Qt::TextAlignmentRole).value<Qt::Alignment>().

CuriousPan

@JonB, it always retruns QFlags<Qt::AlignmentFlag>() 1 which is Qt::DecorationRole, right?

raven-worx

@CuriousPan said in How can I center QCheckBox in QTableView?:

it always retruns QFlagsQt::AlignmentFlag() 1 which is Qt::DecorationRole, right

the Qt::AlignmentFlag flags/enum doesnt contain Qt::DecorationRole, so no
https://doc.qt.io/qt-5/qt.html#AlignmentFlag-enum

CuriousPan

@raven-worx, oh, I see. You're right. Anyway, why is that so?

CuriousPan

@raven-worx, wait! I confused you and me. This '1' is my custom printout. So what you suggested printing just gives following output: QFlags<Qt::AlignmentFlag>()

JonB

@CuriousPan
Qt::AlignLeft 0x0001 Aligns with the left edge.

So this value 1 is left alignment, just as per your picture, and no kind of centering specified, which would have value 4.

CuriousPan

@JonB, yeah, it is, but as I said, no numbers are printed.

JonB

@CuriousPan said in How can I center QCheckBox in QTableView?:

@JonB, it always retruns QFlagsQt::AlignmentFlag() 1 which is Qt::DecorationRole, right?

That's what you wrote. See that 1? Can you please concentrate on one thing at a time.

CuriousPan

@JonB, yep, I can. I'm really sorry for confusing you. No 1 is printed, it's just my mistake.