Keep row selected in QTableView - qt

Question

I am working on a program to view and edit records in a file. It features a QTableView that displays all records, a QLineEdit to search for records, and some labels that display the details of the selected record:
There is a QAbstractTableModel class that holds the data and a QSortFilterProxyModel class that helps filtering the rows in the QTableView.
Searching and filtering works fine. Typing text in the search box immediately filters the list of records. But there are two things I cannot get to work:
if the list is not empty, I want one item to be selected/current always
the selected/current item must be brought into view when typing in the search box
For example, when I type "tesla", the list will be empty since no item matches. But as soon as I backspace to "te", the "Forester" matches and I want it to be selected. Second example: when (after starting the program) I type "f" the list is narrowed down to 8 items and "Pacifica" is selected. When I erase the "f", the Pacifica is still selected but no longer in the visible part of the list.
I have posted the full source code of this on Pastie, and here are some (hopefully) relevant snippets.
void MainWindow::on_lineEditSearch_textChanged(const QString & text)
{
itemProxy->setFilterFixedString(text);
updateStatusBar();
}
void MainWindow::currentRowChangedSlot(QModelIndex const & current, QModelIndex const & /*previous*/)
{
Car * car = 0;
if (current.isValid())
{
QModelIndex sibling = current.sibling(current.row(), COLUMN_THIS);
QVariant variant = itemProxy->data(sibling);
car = static_cast<Car *> (variant.value<void *> ());
}
updateCarMake(car);
updateCarModel(car);
}
MainWindow::MainWindow(QWidget * parent, CarItemModel * itemModel, CarSortFilterProxyModel * itemProxy) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
this->itemModel = itemModel;
this->itemProxy = itemProxy;
ui->setupUi(this);
setupStatusBar();
ui->tableView->setModel(itemProxy);
ui->tableView->setColumnHidden(COLUMN_THIS, true);
QItemSelectionModel * selectionModel = ui->tableView->selectionModel();
connect(selectionModel, SIGNAL(currentRowChanged(QModelIndex const &, QModelIndex const &)),
this, SLOT(currentRowChangedSlot(QModelIndex const &, QModelIndex const &)));
connect(selectionModel, SIGNAL(selectionChanged(QItemSelection const &, QItemSelection const &)),
this, SLOT(selectionChangedSlot(QItemSelection const &, QItemSelection const &)));
ui->tableView->selectRow(0);
ui->lineEditSearch->setFocus();
updateStatusBar();
}
<widget class="QTableView" name="tableView">
<property name="verticalScrollBarPolicy">
<enum>Qt::ScrollBarAlwaysOn</enum>
</property>
<property name="selectionMode">
<enum>QAbstractItemView::SingleSelection</enum>
</property>
<property name="selectionBehavior">
<enum>QAbstractItemView::SelectRows</enum>
</property>
</widget>
So, my question is: how can I make sure an item is always selected and in the visible part of the list (unless the user is scrolling, of course)?

Answer 1

Here's what I did to
always have an item selected, and
have the selected item visible when searching
The solution is even a bit fancier since when going from no visible items to some visible items the most recently selected item will be selected instead of just the first item.
First, I added a QModelIndex lastModelIndex; private member to the MainWindow class, and set it in the SelectionChanged slot. Note that the model index is stored and not the proxy index.
void MainWindow::selectionChangedSlot(QItemSelection const & selected, QItemSelection const & /*deselected*/)
{
if (selected.count() > 0)
{
QModelIndex index = selected.indexes().first();
QModelIndex modelIndex = itemProxy->mapToSource(index);
lastModelIndex = modelIndex;
}
}
Next, I added two methods: ensureSelected() ...
void MainWindow::ensureSelected(QItemSelectionModel * selectionModel, int const proxyCount)
{
if (selectionModel->hasSelection())
{
// an item is currently selected - don't have to do anything
}
else if (proxyCount == 1)
{
// no item is currently selected, but there is exactly one item in the list - select it
QModelIndex proxyIndex = itemProxy->index(0, 0);
selectionModel->setCurrentIndex(proxyIndex, QItemSelectionModel::Select | QItemSelectionModel::Rows);
}
else if (proxyCount > 1)
{
// no item is currently selected, but there are several items in the list
QModelIndex proxyIndex; // !isValid
if (lastModelIndex.isValid())
{
// there's a most recently selected item - compute its index in the list
proxyIndex = itemProxy->mapFromSource(lastModelIndex);
}
if (proxyIndex.isValid())
{
// the most recently selected item is in the list - select it
proxyIndex = proxyIndex.sibling(proxyIndex.row(), COLUMN_THIS);
}
else
{
// there's no most recently selected item or it is no longer in the list - select the first item
proxyIndex = itemProxy->index(0, 0);
}
selectionModel->setCurrentIndex(proxyIndex, QItemSelectionModel::Select | QItemSelectionModel::Rows);
}
else
{
// There are no items in the list - cannot select anything.
}
}
... and ensureVisible():
void MainWindow::ensureVisible(QItemSelectionModel * selectionModel)
{
if (selectionModel->hasSelection())
{
const QModelIndex index = ui->tableView->currentIndex();
ui->tableView->scrollTo(index);
ui->tableView->selectRow(index.row());
ui->tableView->scrollTo(index);
}
}
Weird as it may seem, I have to call scrollTo() twice, or the tableView won't scroll.
These new methods are called from on_lineEditSearch_textChanged() like so:
void MainWindow::on_lineEditSearch_textChanged(const QString & text)
{
itemProxy->setFilterFixedString(text);
QItemSelectionModel * selectionModel = ui->tableView->selectionModel();
int modelCount = itemModel->rowCount(); // number of items in the model
int proxyCount = itemProxy->rowCount(); // number of items in tableview
ensureSelected(selectionModel, proxyCount);
ensureVisible(selectionModel);
updateStatusBar();
}
Please find the updated and complete source code on Pastie.

Answer 2

Handle selection change signal and connect it to your custom slot:
QSortFilterProxyModel *model = new QSortFilterProxyModel(this);
ui->tableView->setModel(model);
connect(ui->tableView->selectionModel(), SIGNAL(selectionChanged(QItemSelection,QItemSelection)), this, SLOT(selectionChanged(QItemSelection,QItemSelection)));
Every time, you table change the current selection the app should select the first item in the model:
void MainWindow::selectionChanged(QItemSelection selected, QItemSelection deselected) {
// Use this
const int rows = ui->tableView->selectionModel()->selectedRows().size();
// or
const int rowCount = selected.size();
// Lets select the first item if there are some items availables
if (rowCount < 1) {
const int availableItems = ui->tableView->model()->rowCount();
if (availableItems > 0) {
const QModelIndex index = ui->tableView->model()->index(0,0);
ui->tableView->selectionModel()->select(index, QItemSelectionModel::ClearAndSelect);
}
}
}
By this way, you should have at least one item selected.