QTreeWidget editItem fails with "edit: editing failed"

Question

I have a QTreeWidgetItem added to a QTreeWidget:

QTreeWidgetItem* item = new QTreeWidgetItem(ui->trwPairs);
item->setFlags(item->flags() | Qt::ItemIsEditable);

If the item is edited, I want to do a few checks on the new value:

Pairs::Pairs(QWidget *parent) :
QWidget(parent),
  ui(new Ui::Pairs)
{
  ui->setupUi(this);
  connect(this->ui->trwPairs, SIGNAL(itemChanged(QTreeWidgetItem*,int)), this, SLOT(Validate(QTreeWidgetItem*,int)));
}

void Pairs::Validate(QTreeWidgetItem* item, int column)
{
  if (item->text(column).toInt() < 1)
  {
    QMessageBox::critical(this, "Error", QString("Node ID ") + item->text(column) +  " is invalid.");
    ui->trwPairs->editItem(item, column);
  }
}

Naturally, if it's less than 1, it catches it, and gives me the message box. However, printed to cerr is edit: editing failed and the item is not in edit mode. What am I missing?

Answer 1

Stepping through it in the debugger reveals the following:

In quabstractitemview.cpp line false is returned on line 3953. Somehow it looks like your item is still in editing state and you are trying to edit it again or something.

bool QAbstractItemViewPrivate::shouldEdit(QAbstractItemView::EditTrigger trigger,
                                          const QModelIndex &index) const
{
// ..
    if (state == QAbstractItemView::EditingState)
      return false;
}

IIRC I had a similar problem with tables with multiple lines per cell. Check out the classes QAbstractItemDelegate views have item delegates which allow you to control which editor is used and how it behaves. I believe by default the QLineEdit is used. Editors like QLineEdit can have validators which control how the data is validated, in your case reject it if the numerical value is < 0. But I think you have to use the model / view classes and implement your own model for that. The Qt documentation for QTreeWidget::setItemWidget(..) says:

This function should only be used to display static content in the place of a tree widget item. If you want to display custom dynamic content or implement a custom editor widget, use QTreeView and subclass QItemDelegate instead.

I am not sure however if there is a simpler way to do this using the widget classes.