Disable Item in Qt Combobox

Question

I can\'t find a standard way to disable an individual item in a Qt combo box. Is there a facility to do this in Qt that I am missing?

Answer 1

Why hack.. We know the model is a QStandardItemModel...

model = dynamic_cast< QStandardItemModel * >( combobox->model() );
item = model->item( row, col );
item->setEnabled( false );

Clean, elegant, and no hack...

Answer 2

You can use the model of a QListWidget as a proxy.

QComboBox *combo = new QComboBox(this);
QListWidget *contents = new QListWidget(combo);
contents->hide();
combo->setModel(contents->model());

/* Populate contents */
contents->addItem("...");    // Etcetera

Then, this method will disable an item:

void disableItem(int index)
{
    QListWidgetItem *item = contents->item(index);
    item->setFlags(item->flags() & ~Qt::ItemIsEnabled);
}

Answer 3

In case your combo box is using a QStandardItemModel (which it does by default) then you may stay away from the Qt::UserRole -1 hack (see blog post to which Desmond refers to in his answer above):

const QStandardItemModel* model = qobject_cast<const QStandardItemModel*>(ui->comboBox->model());
QStandardItem* item = model->item(1);

item->setFlags(disable ? item->flags() & ~(Qt::ItemIsSelectable|Qt::ItemIsEnabled)
                       : Qt::ItemIsSelectable|Qt::ItemIsEnabled));
// visually disable by greying out - works only if combobox has been painted already and palette returns the wanted color
item->setData(disable ? ui->comboBox->palette().color(QPalette::Disabled, QPalette::Text)
                      : QVariant(), // clear item data in order to use default color
              Qt::TextColorRole);

Above code is a revised and more generic solution to my comment to the blog post.

Answer 4

Taken from here:

// Get the index of the value to disable
QModelIndex index = ui.comboBox->model()->index(1, 0); 

// This is the effective 'disable' flag
QVariant v(0);

// the magic
ui.comboBox->model()->setData(index, v, Qt::UserRole - 1);

To enable again use:

QVariant v(1 | 32);

The model used maps the flags word to Qt::UserRole - 1 -- that's what makes this code work. It's not a generic solution that would work with an arbitrary model.