QSortFilterProxyModel and QComboBox

[Armin]

Hi,
I want to sort a QComboBox locale aware, so I used a reimplementation of QSortFilterProxyModel. Unfortunately, it messes up the contents of the QComboBox if I insert Items after calling MyCombo->model()->sort(0);, which does not happen if I just use QSortFilterProxyModel without reimplementing it, so I guess my reimplementation is "naive" and something is missing/wrong.

In the example (stripped to the important stuff, but is compilable) I add A, C, B to the ComboBox, sort it, then I add D and the ComboBox shows <empty line>, A, B, D - and C is missing. Has anybody an idea what I did wrong reimplemnting QSortFilterProxyModel?

Thanks for your help
Armin

Files: (attached also as zip)

main.cpp

#include <QtGui/QApplication>
#include "mainwindow.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

#include <QtGui/QApplication>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

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mysortfilterproxymodel.h

#ifndef MYSORTFILTERPROXYMODEL_H
#define MYSORTFILTERPROXYMODEL_H
 
#include <QtGUI>
 
class MySortFilterProxyModel : public QSortFilterProxyModel
{
  Q_OBJECT
 
public:
  MySortFilterProxyModel(QObject *parent);
  bool lessThan(const QModelIndex &left, const QModelIndex &right) const;
};
#endif // MYSORTFILTERPROXYMODEL_H

#ifndef MYSORTFILTERPROXYMODEL_H
#define MYSORTFILTERPROXYMODEL_H

#include <QtGUI>

class MySortFilterProxyModel : public QSortFilterProxyModel
{
  Q_OBJECT

public:
  MySortFilterProxyModel(QObject *parent);
  bool lessThan(const QModelIndex &left, const QModelIndex &right) const;
};
#endif // MYSORTFILTERPROXYMODEL_H

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mysortfilterproxymodel.cpp

#include "mysortfilterproxymodel.h"
 
MySortFilterProxyModel::MySortFilterProxyModel(QObject *parent) : QSortFilterProxyModel(parent)
{
}
//---------------------------------------------------------------------------
bool MySortFilterProxyModel::lessThan(const QModelIndex &left,
                                      const QModelIndex &right) const
{
  QVariant leftData = sourceModel()->data(left);
  QVariant rightData = sourceModel()->data(right);
 
  QString leftString  = leftData.toString();
  QString rightString = rightData.toString();
 
  return QString::localeAwareCompare(leftString, rightString) < 0;
}

#include "mysortfilterproxymodel.h"

MySortFilterProxyModel::MySortFilterProxyModel(QObject *parent) : QSortFilterProxyModel(parent)
{
}
//---------------------------------------------------------------------------
bool MySortFilterProxyModel::lessThan(const QModelIndex &left,
                                      const QModelIndex &right) const
{
  QVariant leftData = sourceModel()->data(left);
  QVariant rightData = sourceModel()->data(right);

  QString leftString  = leftData.toString();
  QString rightString = rightData.toString();

  return QString::localeAwareCompare(leftString, rightString) < 0;
}

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mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QtGUI>
#include "mysortfilterproxymodel.h"
 
class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
    QComboBox *MyCombo;
    MySortFilterProxyModel *MyProxySortModel;
 
};
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QtGUI>
#include "mysortfilterproxymodel.h"

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();

    QComboBox *MyCombo;
    MySortFilterProxyModel *MyProxySortModel;

};
#endif // MAINWINDOW_H

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mainwindow.cpp

#include "mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
  MyCombo = new QComboBox(this);
  MySortFilterProxyModel *MyProxySortModel = new MySortFilterProxyModel(MyCombo);
  MyProxySortModel->setSourceModel(MyCombo->model());
  MyCombo->model()->setParent(MyProxySortModel);
  MyCombo->setModel(MyProxySortModel);
 
  MyCombo->addItem("A", 1);
  MyCombo->addItem("C", 3);
  MyCombo->addItem("B", 2);
 
  MyCombo->model()->sort(0);
 
  MyCombo->addItem("D", 4);
}
MainWindow::~MainWindow() {}

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
  MyCombo = new QComboBox(this);
  MySortFilterProxyModel *MyProxySortModel = new MySortFilterProxyModel(MyCombo);
  MyProxySortModel->setSourceModel(MyCombo->model());
  MyCombo->model()->setParent(MyProxySortModel);
  MyCombo->setModel(MyProxySortModel);

  MyCombo->addItem("A", 1);
  MyCombo->addItem("C", 3);
  MyCombo->addItem("B", 2);

  MyCombo->model()->sort(0);

  MyCombo->addItem("D", 4);
}
MainWindow::~MainWindow() {}

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comboproxy.zip

[norobro]

Sorry Armin after further testing I discovered my suggestion didn't work.

[Lykurg]

Some point I can add is, that with calling MyCombo->setModel(MyProxySortModel); the "sourceModel()" is deleted:

void QComboBox::setModel(QAbstractItemModel *model)
{
    Q_D(QComboBox);
//...
     if (d->model->QObject::parent() == this)
         delete d->model;

void QComboBox::setModel(QAbstractItemModel *model)
{
    Q_D(QComboBox);
//...
     if (d->model->QObject::parent() == this)
         delete d->model;

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But even if you call a MyCombo->model()->setParent(this); before the problem is not solved...

[norobro]

I found an old thread that states that this was fixed in Qt 4.2. Hmmmmm

I got it to work by using

MyCombo->insertItem(0,"D", 4);

MyCombo->insertItem(0,"D", 4);

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Of course this puts the "D" first so you have to resort. I also tried the following to put the item at the end of the list but got the same result as "addItem()"

MyCombo->insertItem(MyCombo->count(),"D", 4);

MyCombo->insertItem(MyCombo->count(),"D", 4);

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[Lykurg]

I got it to work by using

MyCombo->insertItem(0,"D", 4);

MyCombo->insertItem(0,"D", 4);

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Of course this puts the "D" first so you have to resort.

Instead of manually resort you can try QSortFilterProxyModel::setDynamicSortFilter().

[Armin]

Hi norobro & Lykurg,

many thanks for your ideas, insertItem() instead of addItem() works fine, and dynamic sorting makes it easier. Do you agree that there must be some bug with addItem()? Hope that I can manage all other things which will come up in my little "Qt begiunners project" by myself without taking your time. Sorting things in Qt was/is really a challenge for me :-).

Have a nice day
Armin