Redefining QTreeWidgetItem::operator< - c++

Question

My main goal here is to redefine operator< so that I can sort my columns numerically instead of alphabetically. The code I have so far:
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
//bunch of includes...
#include <QTreeWidgetItem>
#include <QTreeWidget>
extern QSqlDatabase db;
extern QString prefix;
extern QString site;
extern QString dbname;
extern QString user;
namespace Ui {
class mainwindow;
}
class clientinfo;
class mainwindow : public QMainWindow
{
Q_OBJECT
public:
explicit mainwindow(QWidget *parent = 0);
void rPopulate();
void rbookingdisplay();
QPushButton *button;
~mainwindow();
public slots:
//slots...
private:
Ui::mainwindow *ui;
void closeEvent(QCloseEvent *close);
};
class TreeWidgetItem : public QTreeWidgetItem
{
public:
TreeWidgetItem(QTreeWidget *tree) : QTreeWidgetItem(tree) {}
TreeWidgetItem(QTreeWidget * parent, const QStringList & strings)
: QTreeWidgetItem (parent,strings) {}
bool operator< (const QTreeWidgetItem &other) const
{
int sortCol = treeWidget()->sortColumn();
int myNumber = text(sortCol).toInt();
int otherNumber = other.text(sortCol).toInt();
return myNumber < otherNumber;
}
};
#endif // MAINWINDOW_H
and in mainwindow.cpp I have ui->_display->setSortingEnabled(true);
somehow it doesn't use the redefined operator< (the redefined function is never called, it uses the predefined one). Please help.
ui->_abooking->clear();
ui->_abooking->setSortingEnabled(false);
QSqlQuery query;
query.prepare(" SELECT shownumdays, shownumpastdays FROM setting_"+ user +
" WHERE id = 1; ");
query.exec();
query.first();
int days = query.record().value("shownumdays").toInt();
int pastdays = query.record().value("shownumpastdays").toInt();
query.prepare(" SELECT `"+Columns.join("`, `")+
"`,`Currency`, `# of Room` "
" FROM abooking "
" WHERE (DATE_ADD(`Arrival Date`,INTERVAL `Nights` - 1 DAY) >= (CURRENT_DATE - "+ QString::number(pastdays) +") AND "
" (TO_DAYS(`Arrival Date`) + `Nights` - 1 - TO_DAYS(NOW())) <= "+ QString::number(days) +") ");
query.exec();
QString confirm_num = "";
bool flip = true;
while (query.next()){
if (!(confirm_num == query.record().value("Confirmation #").toString())) {
flip = (!flip);
}
QTreeWidgetItem *item = new QTreeWidgetItem();
for (int i = 0; i < Columns.length(); i++) {
if (Columns.at(i) == "Arrival Date") {
item->setText(i, query.record().value(Columns.at(i)).toDate().toString("dd-MM-yyyy"));
} else if ((Columns.at(i) == "Amount Due" || Columns.at(i) == "Paid") && (confirm_num == query.record().value("Confirmation #").toString())) {
item->setText(i, "");
} else if ((Columns.at(i) == "Arrival Time")){
item->setText(i, " " + query.record().value(Columns.at(i)).toTime().toString("hh:mm"));
} else {
item->setText(i, query.record().value(Columns.at(i)).toString());
}
if (Columns.at(i) == "Amount Due" && (!(item->text(i) == ""))) {
item->setTextColor(i, Qt::darkRed);
item->setText(i, item->text(i) + " " + query.record().value("Currency").toString());
} else if (Columns.at(i) == "Room") {
item->setText(i, query.record().value("# of Room").toString() + " " + item->text(i));
}
if (flip) {
item->setBackground(i , Qt::gray);
}
}
if ((!(confirm_num == query.record().value("Confirmation #").toString()))) {
confirm_num = query.record().value("Confirmation #").toString();
ui->_abooking->addTopLevelItem(item);
} else {
ui->_abooking->topLevelItem(ui->_abooking->topLevelItemCount() - 1)->addChild(item);
ui->_abooking->topLevelItem(ui->_abooking->topLevelItemCount() - 1)->setExpanded(true);
}
}
ui->_abooking->setSortingEnabled(true);

Answer 1

You're reimplementing QTreeWidgetItem with a custom class, but then you don't use it when populating the QTreeWidget.
Instead of
QTreeWidgetItem *item = new QTreeWidgetItem();
this should be:
TreeWidgetItem *item = new TreeWidgetItem();
Other than that, your code for operator < looks fine. I'm using the same and it works for me.

Answer 2

bool operator< (const QTreeWidgetItem &other) const
{
int sortCol = treeWidget()->sortColumn();
int myNumber = text(sortCol).toInt();
int otherNumber = other.text(sortCol).toInt();
return myNumber < otherNumber;
}
With reference to your code here above:
I think your problem is that the sort column on the widget remains constant for all QTreeWidgetItems. You have to sort on the value of the item (not the column of the widget):
Therefore the code should look like this:
bool operator< (const QTreeWidgetItem &other) const
{
Q_ASSERT( other.treeWidget() == treeWidget() );
const int col = treeWidget()->sortColumn();
const int role = Qt::DisplayRole;
return( data( col, role ).toInt() < other.data( col, role ).toInt() );
}

Answer 3

The cells are sorted according to the type of data you store in them. You don't need to redefine an operator for that, because QVariant will take care of the comparison for you.
For example, you should use:
item−>setData(0, `Qt::EditRole`, 10);
instead of:
item->setText(0, "10");