Using setData(Qt::EditRole, xxx) with QTableWidgetItem

[VRonin]

There are different approaches here. Do you need a deterministic number of decimals or do you need as many decimals as the number has?
e.g.
data: 12.34500

do you have a 4 digits fixed so 12.3450 or as little digits as necessary to represent the number in full 12.345?

[diverger]

@VRonin I set the data with Qt::EditRole, it's double. When I set the data, the needed decimal count is determined, too. If the data is 12.345, and I need 4 decimal, it should displayed as '12.3450'. If I only need 2 decimal, then it should displayed as '12.35'.

Them problem now is, I want some cells show 4, some cells show 3, and some cells show 2, etc.

[VRonin]

Just use a role

class DecimalsDelegate : public QStyledItemDelegate{
Q_OBJECT
public:
enum { NumOfDecimalsRole = Qt::UserRole + 888 }; /* 888 is just a random number, you can use whatever you want if it conflicts */
explicit DecimalsDelegate(QObject* parent = nullptr)
:QStyledItemDelegate(parent)
{}
virtual ~DecimalsDelegate() = default;
DecimalsDelegate(const DecimalsDelegate&) = delete;
DecimalsDelegate& operator=(const DecimalsDelegate&) = delete;
virtual void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const override
{
    Q_ASSERT(index.isValid());

    QStyleOptionViewItem opt = option;
    initStyleOption(&opt, index);
const QVariant numOfDecimals = index.data(NumOfDecimalsRole );
    if (numOfDecimals.isValid() && !numOfDecimals.isNull() && numOfDecimals.canConvert(QMetaType::Int)  && ( opt.features & QStyleOptionViewItem::HasDisplay) ) {
const QVariant value = index.data(Qt::DisplayRole);
if(value.canConvert(QMetaType::Double))
        opt.text = opt.locale.toString(value.toDouble(),'f',numOfDecimals.toInt());
    }
    const QWidget *widget = option.widget;
    const QStyle* const style = widget ? widget->style() : QApplication::style();
    style->drawControl(QStyle::CE_ItemViewItem, &opt, painter, widget);
}

}

now after you set the Qt::EditRole just set NumOfDecimalsRole to the number of decimals you need

Edit: fixed copy/paste error

[diverger]

@VRonin Great, it work.

I have another idea. Because I can't know the current index of the model in the displayText function. So, I can't change the decimal count by the 'value' 's 'index'. But in 'setEditorData' and 'setModelData', and 'createEditor', I can know the 'index'. So, when I set the widget item, I use '

item->setData(Qt::EditRole, QString::number(ratio_error * 1000, 'f', 2));
ui.testTableWidget->setItem(row, 7, item);

And my derived class is as below:

virtual QWidget *createEditor(QWidget *parent, QStyleOptionViewItem const &option, QModelIndex const &index) const override
	{
		if (index.data(Qt::EditRole).isValid() && ((index.column() == 6) || (index.column() == 7)))
		{
			QDoubleSpinBox *spinbox = new QDoubleSpinBox(parent);
			QTableWidget *table = qobject_cast<QTableWidget *>(this->parent());

			if (index.column() == 6)
			{
				spinbox->setDecimals(2);
			}
			else if (index.column() == 7)
			{
				spinbox->setDecimals(3);
			}
			
			return spinbox;
		}
		else
		{
			return QStyledItemDelegate::createEditor(parent, option, index);
		}
	}

	virtual void iStyledItemDelegate::updateEditorGeometry(QWidget *editor,	QStyleOptionViewItem const &option,
		QModelIndex const &index) const override
	{
		editor->setGeometry(option.rect);
	}

	virtual void iStyledItemDelegate::setEditorData(QWidget *editor, QModelIndex const &index) const override
	{
		if (index.data(Qt::EditRole).isValid() && ((index.column() == 6) || (index.column() == 7)))
		{
			double value = index.model()->data(index, Qt::EditRole).toString().toDouble();
			QDoubleSpinBox *spinBox = qobject_cast<QDoubleSpinBox*>(editor);
			spinBox->setValue(value);
		}
		else
		{
			QStyledItemDelegate::setEditorData(editor, index);
		}
	}

	virtual void setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const override
	{
		if (index.data(Qt::EditRole).isValid() && ((index.column() == 6) || (index.column() == 7)))
		{
			QDoubleSpinBox *spin = qobject_cast<QDoubleSpinBox *>(editor);
			spin->interpretText();
			double value = spin->value();
			int decimals = spin->decimals();
			QString text = QString::number(value, 'f', decimals);
			model->setData(index, text, Qt::EditRole);
		}
		else
		{
			QStyledItemDelegate::setModelData(editor, model, index);
		}
	}

For the column 7 (the last column), it works as expected, but for column 6, when I double click the cell, the value goes to "0.00", and I debuged it, find for column 6, the invoke sequence is:

createEditor -> setEditorData -> setModelData, when invoke the 'setData' in this function, it invoke 'setEditorData' once more. It's right?

[diverger]

@VRonin Finally, I found the reason, I forgot set the minimum and maximum of the spinbox, it seem it's default minimum value is "0", and I just need show a minus float number in column 6. So it is "rounded" to zero.

Can you check my code below, if it's a 'right' usage case?

class iStyledItemDelegate : public QStyledItemDelegate
{
public:
	explicit iStyledItemDelegate(QObject *parent = nullptr)
		: QStyledItemDelegate(parent)
	{}

	virtual ~iStyledItemDelegate() = default;

	virtual QWidget *createEditor(QWidget *parent, QStyleOptionViewItem const &option, QModelIndex const &index) const override
	{
		if ((index.column() == 6) || (index.column() == 7))
		{
			QDoubleSpinBox *spinbox = new QDoubleSpinBox(parent);
			spinbox->installEventFilter(const_cast<iStyledItemDelegate*>(this));
			
			QTableWidget *table = qobject_cast<QTableWidget *>(this->parent());
			spinbox->setFrame(false);
			spinbox->setMinimum(-DBL_MAX);
			spinbox->setMaximum(DBL_MAX);

			if (index.column() == 6)
			{
				spinbox->setDecimals(2);
			}
			else if (index.column() == 7)
			{
				spinbox->setDecimals(3);
			}
		
			return spinbox;
		}
		else
		{
			return QStyledItemDelegate::createEditor(parent, option, index);
		}
	}

	virtual void updateEditorGeometry(QWidget *editor,	QStyleOptionViewItem const &option,
		QModelIndex const &index) const override
	{
		editor->setGeometry(option.rect);
	}

	virtual void setEditorData(QWidget *editor, QModelIndex const &index) const override
	{
		QDoubleSpinBox *spinBox = qobject_cast<QDoubleSpinBox*>(editor);
		
		if (spinBox && ((index.column() == 6) || (index.column() == 7)))
		{
			double value = index.data(Qt::EditRole).toString().toDouble();
			spinBox->setValue(value);
		}
		else
		{
			QStyledItemDelegate::setEditorData(editor, index);
		}
	}

	virtual void setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const override
	{
		QDoubleSpinBox *spin = qobject_cast<QDoubleSpinBox *>(editor);
	
		if (spin && ((index.column() == 6) || (index.column() == 7)))
		{
			spin->interpretText();
			model->setData(index, spin->text(), Qt::EditRole);
		}
		else
		{
			QStyledItemDelegate::setModelData(editor, model, index);
		}
	}
};

[VRonin]

@diverger said in Using setData(Qt::EditRole, xxx) with QTableWidgetItem:

if it's a 'right' usage case

The delegate should never depend on the model or view structure so if (index.column() == is never the right usage case

[diverger]

@VRonin Yes, I know it's not 'good' for 're-use'. But I can't find a method to set delegate to individual cells. In my case, take for example column 6. Some rows may need show 3, some rows may need show 2 decimals, depending on the column 2's contents. So I make this class dedicated to this. Any suggestions to implement my goal but no depending to 'index' in the derived class?

[VRonin]

https://forum.qt.io/topic/71692/using-setdata-qt-editrole-xxx-with-qtablewidgetitem/10

Then set the NumOfDecimalsRole in a slot connected to the dataChanged of the model

Btw, looking at the code above it looks like you need 2 decimals in column 6 and 3 decimals in column 7 and this can be achieved with 2 delegates set on 2 columns with setItemDelegeateForColumn

P.S.

model->setData(index, spin->text(), Qt::EditRole);

this will set a string, not a number so the decimals in a string are meaningless

[diverger]

@VRonin :)，

1. In my previous example, I simplified my usage case.
2. I use strings instead of numbers, because the displayText function won't abandon the trailing zeros of the number strings. I think if I use 'model->setData(index, spin->value(), Qt::EditRole);' , then the displayText() will format the numbers for me, and I can't access 'index' in it, so it will always abandon the trailing zeros.
3. So, my solution is actually avoid using numbers, but use text, and when create editor, I format the text to number, when user finish the editing, I format the values back to text and store it in the model.

[VRonin]

This is a display problem so it should not be handled at the model level. as shown above, the solution is to reimplement paint() in the delegate

[diverger]

@VRonin You are right. Thanks again. :)

[Teddy van Jerry]

It turns out to be a very good method which I seeks for a really long time. But now I use Qt 6.0.0, so the last return statement does not work well. So it needs to be changed into:

return QItemEditorFactory::createEditor(userType, parent);

And it is done!