How to enter and read an Icon image into/from a ListWidget data model with a Delegate

mmesarina

Hi,
I am using a Delegate to retrieve data from a ListWidget data model to be able to control how I display the data in the ListWidgetItem items. My code compiles fine but when I debug the Delegate I can see that the retrieved Icon points to "null". So it seems that the Icon is not being found in the model. I wonder if someone can tell what the problem is. Here are the snippets of the code that are revelant. Thank you!

In MainWindow construtor: I enter the Icon into the data model of ListWidget

@
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent), ui(new Ui::MainWindow)
{
ui->setupUi(this);
QVBoxLayout *hlayout = new QVBoxLayout();
QListWidget *myListWidget = new QListWidget();
// Setting Delegate
myListWidget->setItemDelegate(new ListDelegate(myListWidget));

QListWidgetItem *item = new QListWidgetItem();
QPixmap pixmap(":/images/arrow.png");
QIcon ic(pixmap);
QVariant v(QMetaType::QIcon, &ic);

//Add Icon to model with custom role
item->setData(Qt::UserRole + 3, v);

// Add strings
item->setData(Qt::DisplayRole, "Wine");
//item->setData(Qt::UserRole + 1, "Description");
myListWidget->addItem(item);

// BEER
QListWidgetItem *item2 = new QListWidgetItem();
item2->setData(Qt::DisplayRole, "Beer");
myListWidget->addItem(item2);


myListWidget->setLayout(hlayout);
setCentralWidget(myListWidget);

@

In the Delegate: Read Icon and display in ListWidget--

@
void ListDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
QRect r = option.rect; //rectangle of listitem

// THE FOLLOWING FUNCTION RETURNS A NULL POINTER for ic
QIcon ic = QIcon(qvariant_cast<QPixmap>(index.data(Qt::UserRole + 3)));
r = option.rect.adjusted(5, 10, -10, -10);
ic.paint(painter, r, Qt::AlignVCenter|Qt::AlignRight);
}

@

giesbert

you are casting the cariant to a p9xmap, but it contains an icon.
so add a pixmap in the c'tor or get a qicon out of the variant.

mmesarina

That is so funny, how just telling others about your bug, helps you find the solution. I fiddled some more and realized what you just said so I fixed it. Thanks Gerolf for confirming.

So I replaced this line in the Delegate:
@
QIcon ic = QIcon(qvariant_cast<QPixmap>(index.data(Qt::UserRole + 3)));
@

With:
@

QVariant v = index.data(Qt::UserRole + 3);
QIcon ic = v.value<QIcon>();@

goetz

And instead of

@
QVariant v(QMetaType::QIcon, &ic);
@

it is ok to write (and you actually should do this):

@
QVariant v(ic);
@