QItemSelectionModel::currentChanged and revert change

[Lykurg]

Hi,

I have a QListView and connect the signal from its selection model ItemSelectionModel::currentChanged(const QModelIndex &current, const QModelIndex &previous) to my slot. In that slot I want to revert the change. But I fail. How to revert an selection?

Example:

#include <QtGui>
#include "test.h"
 
int main(int argc, char **argv)
{
  QApplication app(argc, argv);
 
  Test w;
  w.show();
 
  return app.exec();
}

#include <QtGui>
#include "test.h"

int main(int argc, char **argv)
{
  QApplication app(argc, argv);
   
  Test w;
  w.show();

  return app.exec();
}

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#ifndef TEST_H
#define TEST_H
 
#include <QtGui>
 
class Test : public QWidget
{
  Q_OBJECT
  public:
    Test(QWidget *parent = 0);
    QListView *v;
    bool canceled;
 
  public slots:
    void changed( const QModelIndex & current, const QModelIndex & previous );
};
#endif

#ifndef TEST_H
#define TEST_H

#include <QtGui>

class Test : public QWidget
{
  Q_OBJECT
  public:
    Test(QWidget *parent = 0);
    QListView *v;
    bool canceled;

  public slots:
    void changed( const QModelIndex & current, const QModelIndex & previous );
};
#endif

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#include "test.h"
#include <QtGui>
 
Test::Test(QWidget *parent) 
  : QWidget(parent)
{
  QLayout *l = new QHBoxLayout(this);
  v = new QListView(this);
  v->setSelectionMode(QAbstractItemView::SingleSelection);
  QStringListModel *model = new QStringListModel();
  QStringList list;
  list << "a" << "b" << "c" << "d" << "e" << "f";
  model->setStringList(list);
  v->setModel(model);
  l->addWidget(v);
  setLayout(l);
  v->setCurrentIndex(model->index(0,0));
  connect(v->selectionModel(), SIGNAL(currentChanged(const QModelIndex& , const QModelIndex&)), this, SLOT(changed(const QModelIndex& , const QModelIndex&)));
  canceled = false;
}
 
void Test::changed( const QModelIndex & current, const QModelIndex & previous )
{
  qWarning() << current << previous;
  if (canceled)
  {
    canceled = false;
    return;
  }
 
  QMessageBox msgBox;
  msgBox.setStandardButtons(QMessageBox::Discard | QMessageBox::Cancel);
  int ret = msgBox.exec();
  switch (ret)
  {
    case QMessageBox::Discard:
      break;
    case QMessageBox::Cancel:
      canceled = true;
      v->selectionModel()->setCurrentIndex(previous, QItemSelectionModel::ClearAndSelect); // no "back change"
      //v->setCurrentIndex(previous); // all lines between current and previous are selected
      return;
      break;
  }
}

#include "test.h"
#include <QtGui>

Test::Test(QWidget *parent) 
  : QWidget(parent)
{
  QLayout *l = new QHBoxLayout(this);
  v = new QListView(this);
  v->setSelectionMode(QAbstractItemView::SingleSelection);
  QStringListModel *model = new QStringListModel();
  QStringList list;
  list << "a" << "b" << "c" << "d" << "e" << "f";
  model->setStringList(list);
  v->setModel(model);
  l->addWidget(v);
  setLayout(l);
  v->setCurrentIndex(model->index(0,0));
  connect(v->selectionModel(), SIGNAL(currentChanged(const QModelIndex& , const QModelIndex&)), this, SLOT(changed(const QModelIndex& , const QModelIndex&)));
  canceled = false;
}

void Test::changed( const QModelIndex & current, const QModelIndex & previous )
{
  qWarning() << current << previous;
  if (canceled)
  {
    canceled = false;
    return;
  }

  QMessageBox msgBox;
  msgBox.setStandardButtons(QMessageBox::Discard | QMessageBox::Cancel);
  int ret = msgBox.exec();
  switch (ret)
  {
    case QMessageBox::Discard:
      break;
    case QMessageBox::Cancel:
      canceled = true;
      v->selectionModel()->setCurrentIndex(previous, QItemSelectionModel::ClearAndSelect); // no "back change"
      //v->setCurrentIndex(previous); // all lines between current and previous are selected
      return;
      break;
  }
}

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Thanks for any help.

[spirit]

looks and works fine. maybe I don't understand something.
when I selected an item a message box appeared. I pressed "cancel" and cursor has been set on previous item.
edited: ah, I see. when mouse is used then reverting is wrong. works fine for keyboard.

[spirit]

looks like this works
h-file

...
public slots:
    void changed( const QModelIndex & current, const QModelIndex & previous );
	void restoreSlot(const QModelIndex &index);
 
signals:
	void restore(const QModelIndex &index);
...

...
public slots:
    void changed( const QModelIndex & current, const QModelIndex & previous );
	void restoreSlot(const QModelIndex &index);
 
signals:
	void restore(const QModelIndex &index);
...

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cpp-file

...
connect(this, SIGNAL(restore(const QModelIndex &)), this, SLOT(restoreSlot(const QModelIndex &)), Qt::QueuedConnection);
...
void Test::changed( const QModelIndex & current, const QModelIndex & previous )
{
  qWarning() << current << previous;
  if (canceled)
  {
    canceled = false;
    return;
  }
 
  QMessageBox msgBox;
  msgBox.setStandardButtons(QMessageBox::Discard | QMessageBox::Cancel);
  int ret = msgBox.exec();
  switch (ret)
  {
    case QMessageBox::Discard:
      break;
    case QMessageBox::Cancel:		
      canceled = true;
      //v->selectionModel()->setCurrentIndex(previous, QItemSelectionModel::ClearAndSelect); // no "back change"	  
      //v->setCurrentIndex(previous); // all lines between current and previous are selected	  	  	  
	  emit restore(previous);
      return;
      break;
  }
}
 
void Test::restoreSlot(const QModelIndex &index)
{
	v->setCurrentIndex(index);
}

...
connect(this, SIGNAL(restore(const QModelIndex &)), this, SLOT(restoreSlot(const QModelIndex &)), Qt::QueuedConnection);
...
void Test::changed( const QModelIndex & current, const QModelIndex & previous )
{
  qWarning() << current << previous;
  if (canceled)
  {
    canceled = false;
    return;
  }
 
  QMessageBox msgBox;
  msgBox.setStandardButtons(QMessageBox::Discard | QMessageBox::Cancel);
  int ret = msgBox.exec();
  switch (ret)
  {
    case QMessageBox::Discard:
      break;
    case QMessageBox::Cancel:		
      canceled = true;
      //v->selectionModel()->setCurrentIndex(previous, QItemSelectionModel::ClearAndSelect); // no "back change"	  
      //v->setCurrentIndex(previous); // all lines between current and previous are selected	  	  	  
	  emit restore(previous);
      return;
      break;
  }
}

void Test::restoreSlot(const QModelIndex &index)
{
	v->setCurrentIndex(index);
}

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[Lykurg]

It's amazing how fast this board is! I was just out for spot, came back, got an answer, tried it, works fine, thanks!

The problem is also that qt needs time to revers the selection because without Qt::QueuedConnection it will fail. And it's curios that it doesn't respect the QAbstractItemView::SingleSelection. Is this a thing one could not change or maybe the trolls could? Should we inform them? I don't know, I don't understand all of the issue exact.

[Lykurg]

Ok, the "real" problem was the signal-slot binding. If i directly use

connect(v->selectionModel(), SIGNAL(currentChanged(const QModelIndex& , const QModelIndex&)), this, SLOT(changed(const QModelIndex& , const QModelIndex&)), Qt::QueuedConnection);

connect(v->selectionModel(), SIGNAL(currentChanged(const QModelIndex& , const QModelIndex&)), this, SLOT(changed(const QModelIndex& , const QModelIndex&)), Qt::QueuedConnection);

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all works as expected without the additional signal.

[spirit]

nice, I've just posted a solution without investigation.