Can't get item from QTreeView by QModelIndex - c++

Question

I create a QTreeView in a window, and I want to get the text of selected items when double clicking them. I try to use the signal "doubleClicked(const QModelIndex &)" to get the index of selected item.
But when I received the signal and wanted to do something with the index passed in, I can't get the item properly.
I found the index passed in is something like that:
root
|...item1 (0, 0)
|...|...subItem1 (0, 0)
|...|...subitem2 (1, 0)
|...item2 (1, 0)
There are two (0, 0) and (1, 0) items???
EDIT: I got this result by
qDebug(QString::number(index.row()).toLatin1().data()); // row
qDebug(QString::number(index.column()).toLatin1().data()); // column
Here is my code, create QTreeView and QStandardItemModel:
mTree = new QTreeView(this); // mTree is a class member
treeModel = new QStandardItemModel(); // also a class member
proxymodel = new MySortFilterProxyModel(); // for sorting
proxymodel->setSourceModel(treeModel);
mTree->setModel(proxymodel);
and a custom slot to receive the signal:
private slots:
void getSelectedIP(const QModelIndex &);
connect signal and slot:
connect(mTree, SIGNAL(doubleClicked(const QModelIndex &)),
this, SLOT(getSelectedIP(const QModelIndex &)));
implementation of the slot, and the program crashed in this code:
void HostTreeFrame::getSelectedIP(const QModelIndex &index)
{
QStandardItem *selectedItem = treeModel->itemFromIndex(index);
qDebug(QString::number(index.row()).toLatin1().data());
qDebug(QString::number(index.column()).toLatin1().data());
qDebug("1");
QString selectedIPString = selectedItem->text(); // program crashed here, selectedItem == nullptr
qDebug("2");
}
EDIT:
The selectedItem is nullptr, that's why the program crashed, but why it is nullptr?

Answer 1

Consider the code...
void HostTreeFrame::getSelectedIP(const QModelIndex &index)
{
QStandardItem *selectedItem = treeModel->itemFromIndex(index);
The problem is that index is associated with the model being used by the view but that's the proxy model -- not the QStandardItemModel.
You need to map the model index index to the correct model. So something like...
void HostTreeFrame::getSelectedIP(const QModelIndex &index)
{
auto standard_item_model_index = proxymodel->mapToSource(index);
QStandardItem *selectedItem = treeModel->itemFromIndex(standard_item_model_index);
/*
* Check selectedItem before dereferencing.
*/
if (selectedItem) {
...
The code above assumes proxymodel is a member of (or is directly visible to) HostTreeFrame.