I am trying to create a custom editor for a user datatype to show in a model-view . Here is want I have:

Custom data type btRule (class), registered with Q_DECLARE_METATYPE(btRule)

Model btRulesModel that returns btRule for editing:
Qt Code: 
  1. QVariant btRulesModel::data(const QModelIndex& index, int role) const
  2. {
  3. btRule& rul = _rules[index.row()];
  4. …
  5. if ( (role == Qt::EditRole) && (index.column() == 1))
  6. 	{
  8. 		v.setValue(rul);
  9. 		return v;
  10. 	}
  11. …
  12. }
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I have class ModelParamViewer derived from QStyledItemDelegate. In the constructor I am registering custom editor
Qt Code: 
  1. ModelParamViewer::ModelParamViewer(QObject *parent)
  2. 		: QStyledItemDelegate(parent)
  3. 	{
  4. 		QItemEditorCreator<ParamEditor>* itemCreator =
  5. 			new QItemEditorCreator<ParamEditor>("btRules");
  6.  
  8. 		btRule br;
  9. 		v.setValue(br);
  11. 		this->setItemEditorFactory(factory);  
  12. 		QItemEditorFactory* editorfactory = this->itemEditorFactory();
  13. 		editorfactory->registerEditor(v.type(), itemCreator);
  14. 	}:
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And I am showing the editor in
Qt Code: 
  1. QWidget* ModelParamViewer::createEditor(QWidget *parent, 
  2. 	const QStyleOptionViewItem& option,
  3. 	const QModelIndex& index) const
  4. 	{
  5. …
  6. 			ParamEditor* wdg= new ParamEditor(parent);
  7. 			//QComboBox* wdg = new QComboBox(parent);
  8. 			return wdg;
  9. 	}
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My custome editor is:
Qt Code: 
  1. class ParamEditor : public QWidget
  2. 	{
  3. 		Q_OBJECT
  4. 	public:
  5. 		ParamEditor  (QWidget* parent = 0) : QWidget(parent)
  6. 		{
  7. 			QString ss("QSpinBox{background-color: #ABABAB;border: 1px solid black;}");
  8. 			setStyleSheet(ss); 
  9. 			setMinimumWidth(200);
  10. 			QHBoxLayout* layout = new QHBoxLayout();
  11. 			setLayout(layout);
  12. 			QLabel* lbl = new QLabel"label 1", this);
  13. 			layout->addWidget(lbl);
  14. 		}
  15. 	};
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Question:
when I am in the edit mode the editor does not show up. However, when I am replacing editor with ComboBox – combobox shows up as the editor. I understand that ComboBox, just like QLabel, are some of the default editors for the regular datatypes. What am I doing wrong here?