Custom Delegate

shahriar25

Hi,
II'm working on a music player and I want to build a custom Delegate for my album QListWidget. I just want to add a artist name under the QListWidgetItem's title.
I have looked at some custom Delegate examples in Qt examples but they are too complicated.
Can someone tell me the simplest way?

mrjj

Hi
You could add \n (newline) between text
and it will be drawn as one item like:
My Song Title
Artist

QString Row=QString("%1\n%2").arg("My Song Title").arg("Artist");
ui->listWidget->addItem(Row);

shahriar25

Hi,
thank you. I did it. but still is there a simple example about custom delegates?

And also is it possible to sort a QListWidget with item's userRole Data ( listWidgetItem->Data(Qt::UserRole) ) ?

Chris Kawa

Here's a little example of a delegate that takes title and artist from user roles of the index:

struct MyDelegate: public QStyledItemDelegate
{
    MyDelegate(QObject* parent = nullptr) : QStyledItemDelegate(parent) {}

    void paint(QPainter* p, const QStyleOptionViewItem& o, const QModelIndex& idx) const override
    {
        // get the data from the index
        auto title  = idx.data(Qt::UserRole).toString();
        auto artist = idx.data(Qt::UserRole+1).toString();

        //split cell rectangle into upper and lower half
        auto titleRect  = o.rect.adjusted(0, 0, 0, -o.rect.height()/2);
        auto artistRect = o.rect.adjusted(0, o.rect.height()/2, 0, 0);

        //draw the data in their rectangles
        p->drawText(titleRect, Qt::AlignLeft, title);
        p->drawText(artistRect, Qt::AlignLeft, artist);
    }

    QSize sizeHint(const QStyleOptionViewItem& o, const QModelIndex& idx) const override
    {
        //get the default size hint
        auto sh = QStyledItemDelegate::sizeHint(o, idx);
        //modify the hint to fit 2 lines of text
        return QSize(sh.width(), sh.height()*2);
    }
};

You can play around with the painter, fonts, alignment etc. but that's the basic idea.

AFAIK you can't select a role for sorting in a QListWidget, but you could use a QListView with a QStandardItemModel instead. Should be pretty similar to use and that model allows you to set a role used for sorting.

shahriar25

Hi,
Thank you for the example it helped so much.
and for the listView:
I'm using QListWdgetItem for the albums but there is no addItem or insertItem in QListView.
What should I do about that?

Chris Kawa

When using a QListView you need to provide a model via setModel(). I suggest a QStandardItemModel. In that setup you add items to the model, not to the view, i.e. use setItem() to insert a QStandardItem.

shahriar25

Hi,
setModel in QListView takes an QAbstractItemModel not a QStandardModel. and I looked at the QAbstractItemModel and I got confused. Where are it's items?

Chris Kawa

QAbstractItemModel is an abstract base class for models. It does not have items because not all models need them (e.g. QSqlTableModel).

QStandardModel is one of the implementations of QAbstractItemModel that Qt provides. You can pass it to the setModel() method. It uses QStandardItem as the item type.

shahriar25

Yes you're right I made a mistake.
thank you. you helped so much

shahriar25

Hi,
I did as you said but it doesn't sort

QStandardItemModel *model = new QStandardItemModel;
QStandardItem *item = new QStandardItem("Daze");
QStandardItem *item2 = new QStandardItem("Jealous Gods");
model->setItem(0,item2);
model->setItem(1, item);
model->setSortRole(0);
ui->listView->setModel(model);

it shows:
Jealous Gods
daze

Chris Kawa

You need to call sort() to sort the model. Also you should use enums and not raw role numbers in case the value changes in the future:

QStandardItemModel *model = new QStandardItemModel(someParent); //remember to give it a parent or it leaks!
model->setItem(0, new QStandardItem("Jealous Gods"));
model->setItem(1, new QStandardItem("Daze"));
model->setSortRole(Qt::DisplayRole); // Qt::DisplayRole is default anyway, so this changes nothing
model->sort(0);
ui->listView->setModel(model);

shahriar25

Yes thank you so much