QListWidget back to previous item in currentItemChanged

[laszlo.gosztola]

Hi all,

I found an interesting problem. I use a QListWidget for selection between items. I would like to ask the user if he is sure to change the current item. My plan is to use the currentItemChanged signal of the QListWidget, because it has the previous item pointer.

Sample code:

#include "mainwidget.h"
 
#include <QListWidget>
#include <QGridLayout>
 
#include <QMessageBox>
#include <QTimer>
 
MainWidget::MainWidget(QWidget *parent) : QWidget(parent)
{
    list = new QListWidget(this);
 
    QGridLayout* mainLayout = new QGridLayout();
    mainLayout->addWidget(list);
    setLayout(mainLayout);
 
    list->addItem("Item1");
    list->addItem("Item2");
    list->addItem("Item3");
    list->addItem("Item4");
 
    connect(list, SIGNAL(currentItemChanged(QListWidgetItem*,QListWidgetItem*)), this, SLOT(currentItemChanged(QListWidgetItem*,QListWidgetItem*)));
}
 
MainWidget::~MainWidget()
{
    delete list;
}
 
void MainWidget::currentItemChanged(QListWidgetItem *current, QListWidgetItem *previous)
{
    qDebug("CurrentItemChanged - Index: %d", list->row(current));
    if ( list->row(current) == currentRow )
    {
        return;
    }
    if ( QMessageBox::No == QMessageBox::question(this, "Question", "Really want to change?", QMessageBox::Yes | QMessageBox::No) )
    {
        //TODO: change back to the previous item
        list->setCurrentItem(previous);
    }
}

#include "mainwidget.h"

#include <QListWidget>
#include <QGridLayout>

#include <QMessageBox>
#include <QTimer>

MainWidget::MainWidget(QWidget *parent) : QWidget(parent)
{
    list = new QListWidget(this);

    QGridLayout* mainLayout = new QGridLayout();
    mainLayout->addWidget(list);
    setLayout(mainLayout);

    list->addItem("Item1");
    list->addItem("Item2");
    list->addItem("Item3");
    list->addItem("Item4");

    connect(list, SIGNAL(currentItemChanged(QListWidgetItem*,QListWidgetItem*)), this, SLOT(currentItemChanged(QListWidgetItem*,QListWidgetItem*)));
}

MainWidget::~MainWidget()
{
    delete list;
}

void MainWidget::currentItemChanged(QListWidgetItem *current, QListWidgetItem *previous)
{
    qDebug("CurrentItemChanged - Index: %d", list->row(current));
    if ( list->row(current) == currentRow )
    {
        return;
    }
    if ( QMessageBox::No == QMessageBox::question(this, "Question", "Really want to change?", QMessageBox::Yes | QMessageBox::No) )
    {
        //TODO: change back to the previous item
        list->setCurrentItem(previous);
    }
}

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That was my first idea, but of course it asks again the question, so I tried to temporally disable signals

if ( QMessageBox::No == QMessageBox::question(this, "Question", "Really want to change?", QMessageBox::Yes | QMessageBox::No) )
    {
        //TODO: change back to the previous item
        list->blockSignals(true);
        list->setCurrentItem(previous);
        list->blockSignals(false);
    }

if ( QMessageBox::No == QMessageBox::question(this, "Question", "Really want to change?", QMessageBox::Yes | QMessageBox::No) )
    {
        //TODO: change back to the previous item
        list->blockSignals(true);
        list->setCurrentItem(previous);
        list->blockSignals(false);
    }

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The problem with this is that the current item changes back to the previous item, but the selection not and I don't really understand this behaviour.
For a workaround, I have this solution, but I think it's not very elegant.

void MainWidget::currentItemChanged(QListWidgetItem *current, QListWidgetItem *previous)
{
    qDebug("CurrentItemChanged - Index: %d", list->row(current));
    if ( list->row(current) == currentRow )
    {
        return;
    }
    if ( QMessageBox::No == QMessageBox::question(this, "Question", "Really want to change?", QMessageBox::Yes | QMessageBox::No) )
    {
        //TODO: change back to the previous item
        QTimer::singleShot(0, this, SLOT(goBack()));
    }else
    {
        currentRow = list->row(current);
    }
}
 
void MainWidget::goBack()
{
    qDebug("GoBack: %d", currentRow);
    list->setCurrentRow(currentRow);
}

void MainWidget::currentItemChanged(QListWidgetItem *current, QListWidgetItem *previous)
{
    qDebug("CurrentItemChanged - Index: %d", list->row(current));
    if ( list->row(current) == currentRow )
    {
        return;
    }
    if ( QMessageBox::No == QMessageBox::question(this, "Question", "Really want to change?", QMessageBox::Yes | QMessageBox::No) )
    {
        //TODO: change back to the previous item
        QTimer::singleShot(0, this, SLOT(goBack()));
    }else
    {
        currentRow = list->row(current);
    }
}

void MainWidget::goBack()
{
    qDebug("GoBack: %d", currentRow);
    list->setCurrentRow(currentRow);
}

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Do You have any explanation why this workaround works, and why the selection doesn't go back if I call it from the slot directly? Is it normal? Do You have any idea for a more elegant solution?

Thanks!

[Spitfire]

You need to update selection model as well and because you block the signals model doesn't get updated.

Anyway, another solution could be to install event filter on the List widget, and capture mouse release or key up/down (whatever lets you change current item).
There you can show your dialog and if the user cancels it, you can return true to filter out the event and prevent anything from happening.

[laszlo.gosztola]

Thanks, I will try to update the selection model also.