QTreeWidgetItem issue: Items set using setWidgetItem are dispearring after moving - qt

Question

I have a bunch of QTreeWidgetItems that have embedded widgets in them that i set using the setItemWidget() function in the QTreeWidgetItem class.
Problem is anytime I move QTreeWidgetItem using drag/drop or any other means the embedded widget I set before disappears. I've seen around various forums that others have had this same problem (see link below)
http://www.qtcentre.org/threads/40500-QTreeWidget-setItemWidget%28%29-item-disappears-after-moving-item
Any possible solutions?

Answer 1

The problem is caused by QTreeWidget's implementation. When items are moved within the model, it deletes items at old positions and recreates them at new positions. We need to ensure 3 thinngs:
Rescue embedded widget from being deleted when its item is deleted.
Attach some information to items so we can track them and choose which widget belongs to an item.
Re-insert widget after item is moved.
Here is proof-of-concept implementation. Tree_widget_keeper_wrapper ensures 1st objective, setItemWidget's reimplementation ensures the 2nd one, and rows_inserted slot ensures the 3rd one. I tested that it works but it should be improved before using in real projects. Qt::UserRole should be changed to a configurable role. We should use role that is not used by the model itself. I put all implementation to class declaration to make it more readable but you should separate them in real code.
class Tree_widget_keeper_wrapper : public QWidget {
Q_OBJECT
public:
Tree_widget_keeper_wrapper(QWidget* child) {
_child = child;
QVBoxLayout* layout1 = new QVBoxLayout(this);
layout1->setContentsMargins(0, 0, 0, 0);
layout1->addWidget(_child);
}
~Tree_widget_keeper_wrapper() {
if (_child->parent() == this) {
_child->hide();
_child->setParent(0);
}
}
private:
QWidget* _child;
};
class Fixed_tree_widget : public QTreeWidget {
Q_OBJECT
public:
Fixed_tree_widget(QWidget* parent) : QTreeWidget(parent) {
connect(model(), SIGNAL(rowsInserted(QModelIndex,int,int)),
this, SLOT(rows_inserted(QModelIndex,int,int)));
}
void setItemWidget(QTreeWidgetItem* item, int column, QWidget* widget) {
QTreeWidget::setItemWidget(item, column, new Tree_widget_keeper_wrapper(widget));
item->setData(column, Qt::UserRole, all_widgets.count());
all_widgets << widget;
}
private:
QWidgetList all_widgets;
private slots:
void rows_inserted(QModelIndex parent, int start, int end) {
for(int column = 0; column < model()->columnCount(parent); column++) {
for(int row = start; row <= end; row++) {
QModelIndex index = model()->index(row, column, parent);
QVariant data = model()->data(index, Qt::UserRole);
if (data.type() == QVariant::Int) {
int i = data.toInt();
QTreeWidgetItem* item = itemFromIndex(index);
if (item && i >= 0 && i < all_widgets.count()) {
setItemWidget(item, column, all_widgets[i]);
all_widgets[i]->show();
}
}
}
}
}
};
I tested it against InternalMove mode and dragging items with mouse. Maybe in some other cases you will need to listen to other model's signals.