QItemDelegate use in QTableWidget

[spirit]

in QCLDelegate::createEditor you should write additional condition

QWidget *QCLDelegate::createEditor(QWidget *parent,
                                     const QStyleOptionViewItem & /* option */,
                                     const QModelIndex &index) const           
{
   if (index.column() == 2 || index.column() == 3 || index.column() == 4) {
      //creating and customization of comboboxes
      return comboBox;
   }
 
   return new QLineEdit(parent);
}

QWidget *QCLDelegate::createEditor(QWidget *parent,
                                     const QStyleOptionViewItem & /* option */,
                                     const QModelIndex &index) const           
{
   if (index.column() == 2 || index.column() == 3 || index.column() == 4) {
      //creating and customization of comboboxes
      return comboBox;
   }

   return new QLineEdit(parent);
}

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you also should be careful in other Delegate's method where an editor is used as method's parameter, you should cast each editor to concert type, because now you have two different editor's type -- QComboBox and QLineEdit.