QListWidget item at 0th index is selected by default - c++

Question

I have a QListWidget which has some item, and I have "Remove" button on my form which actually removes item from list. Problem is that when form load for first time and I press remove without selecting any item from list, it takes the item at 0th index by default and remove it. Following is the code segment:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
ui->listWidget->addItem(new QListWidgetItem("Item1"));
ui->listWidget->addItem(new QListWidgetItem("Item2"));
ui->listWidget->addItem(new QListWidgetItem("Item3"));
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_btnRemove_clicked()
{
printf("on_btnRemove_clicked() \n");
int currentRow = ui->listWidget->currentRow();
QModelIndex currentIndex = ui->listWidget->currentIndex();
QListWidgetItem* currentItem = ui->listWidget->currentItem();
printf("currentRow: %d\n", currentRow);
if(currentRow > -1) {
printf("currentIndex.data() %s: \n", currentIndex.data().toString().toStdString().c_str());
printf("currentItem->data(0): %s \n", currentItem->data(0).toString().toStdString().c_str());
QListWidgetItem* itemToDelete = ui->listWidget->takeItem(currentRow);
delete itemToDelete;
itemToDelete = NULL;
}
}
Any idea how to override this behavior or at least anyway that I can show that 0th index is selected with default blue background of item.

Answer 1

You can show the selected item after adding the items, by calling setCurrentItem:-
QListWidgetItem* pSelectedItem = new QListWidgetItem("Item1");
ui->listWidget->addItem(pSelectedItem);
ui->listWidget->addItem(new QListWidgetItem("Item2"));
ui->listWidget->addItem(new QListWidgetItem("Item3"));
ui->listWidget->setCurrentItem(pSelectedItem);
As the docs state: -
Unless the selection mode is NoSelection, the item is also be selected.
Alternatively, rather than retrieving the current Item, get the selected items with selectedItems(), which I would expect to return an empty list with which you can check the number of items: -
if(ui->listWidget->selectedItems().count())
{
// delete items
}
Note that a call to clearSelection states:-
Deselects all selected items. The current index will not be changed.
I would expect this means that requesting the current index or current item can return a valid index or item, which is why delete removes the item, even though it is not selected.

Answer 2

You can use the function setCurrentRow from QListWidget:
// Set the first row as current
ui->listWidget->setCurrentRow(0);
and add a blue background color with:
// Get default background color
QBrush defaultBrush = ui->listWidget->currentItem->background();
// Set background color
QBrush brush(Qt::blue);
ui->listWidget->currentItem->setBackground(brush);
to set the default color:
// Change background color with default color
ui->listWidget->currentItem->setBackground(defaultBrush);

Answer 3

Although it's a many-years-old question, recently I came across a similar problem and solved the problem by overriding the behavior mentioned by the op. To help people who are dealing with the same problem but are not satisfied with the accepted answer, I'll post my alternative solution here.
I found the weird behavior comes from QAbstractItemView::focusInEvent.
As shown below by the snippet from Qt source code, when a QListWidget (or whatever widget that inherits QAbstractItemView) receives a non-mouse focus event, its first item becomes its current item automatically if there isn't a current item.
// code.woboq.org/qt5/qtbase/src/widgets/itemviews/qabstractitemview.cpp.html#_ZN17QAbstractItemView12focusInEventEP11QFocusEvent
void QAbstractItemView::focusInEvent(QFocusEvent *event)
{
Q_D(QAbstractItemView);
QAbstractScrollArea::focusInEvent(event);
const QItemSelectionModel* model = selectionModel();
bool currentIndexValid = currentIndex().isValid();
if (model
&& !d->currentIndexSet
&& !currentIndexValid) {
bool autoScroll = d->autoScroll;
d->autoScroll = false;
QModelIndex index = moveCursor(MoveNext, Qt::NoModifier); // first visible index
if (index.isValid() && d->isIndexEnabled(index) && event->reason() != Qt::MouseFocusReason) {
selectionModel()->setCurrentIndex(index, QItemSelectionModel::NoUpdate);
currentIndexValid = true;
}
d->autoScroll = autoScroll;
}
if (model && currentIndexValid)
setAttribute(Qt::WA_InputMethodEnabled, (currentIndex().flags() & Qt::ItemIsEditable));
else if (!currentIndexValid)
setAttribute(Qt::WA_InputMethodEnabled, false);
d->viewport->update();
}
To override this behavior, make a subclass of QListWidget and override focusInEvent() along with focusOutEvent() in the subclass.
virtual void focusInEvent(QFocusEvent *event) override {
// bypass QAbstractItemView::focusInEvent
QAbstractScrollArea::focusInEvent(event);
}
virtual void focusOutEvent(QFocusEvent *event) override {
// bypass QAbstractItemView::focusOutEvent
QAbstractScrollArea::focusOutEvent(event);
}