Subclassing QComboBox to have Checkboxes

[HunterMetcalfe]

As the title states I'd like to have the items in my QComboBox to have check boxes. I've subclassed QStandardItemModel in order to do so, but it isn't working. I get the items, but no checkboxes. Normally when I want checkboxes in a QTableView I reimplement the flags function. I've seen where individuals override the addItem function of QCombox and then set the QComboBox to be editable, but that isn't desired as I don't want to give the user the ability to add items into the combo box and I would think, as with other Qt Model/View classes, this would work similarly.

Header:

#ifndef CHECKABLECOMBOBOX_HPP
#define CHECKABLECOMBOBOX_HPP

#include <QStandardItemModel>
#include <QComboBox>

class CCheckableComboBoxModel : public QStandardItemModel
{
   Q_OBJECT
public :
   CCheckableComboBoxModel( QObject * parent = nullptr ) ;
   ~CCheckableComboBoxModel() ;

protected :
   virtual QVariant data( const QModelIndex &index, int role ) const ;
   virtual Qt::ItemFlags flags( const QModelIndex & index ) const ;
   virtual bool setData( const QModelIndex & index, const QVariant & value, int role ) ;

signals :
   void CheckStateChanged( bool checked, const QString & item ) ;
} ;

class CCheckableComboBox : public QComboBox
{
   Q_OBJECT
public :
   CCheckableComboBox( QWidget * parent = nullptr ) ;
   ~CCheckableComboBox() ;

protected :
   CCheckableComboBoxModel * m_model ;
} ;

#endif // CHECKABLECOMBOBOX_HPP

Source

#include "CheckableComboBox.hpp"

CCheckableComboBoxModel::CCheckableComboBoxModel( QObject * parent ) :
   QStandardItemModel( parent )
{

}

CCheckableComboBoxModel::~CCheckableComboBoxModel()
{

}

QVariant CCheckableComboBoxModel::data( const QModelIndex & index, int role ) const
{
   QVariant retval ;
   if( !index.isValid() )
   {
      return retval ;
   }

   QStandardItem * standardItem = item( index.row(), index.column() ) ;

   printf( "Item is checkable %d!\n", standardItem->isCheckable() ) ;

   if( standardItem != nullptr )
   {
      switch( role )
      {
         case Qt::CheckStateRole :
            return standardItem->checkState() ;
         case Qt::DisplayRole :
            return standardItem->text() ;
         default :
            break ;
      }
   }

   return retval ;
}

Qt::ItemFlags CCheckableComboBoxModel::flags( const QModelIndex & index ) const
{
   Q_UNUSED( index ) ;
   return Qt::ItemIsUserCheckable | Qt::ItemIsEnabled | Qt::ItemIsSelectable | Qt::ItemIsEditable ;
}

bool CCheckableComboBoxModel::setData( const QModelIndex & index, const QVariant & value, int role )
{
   bool retval = false ;

   if( index.isValid() && role == Qt::CheckStateRole )
   {
      //get the item
      QStandardItem * standardItem = item( index.row(), index.column() ) ;

      Qt::CheckState checkState = ( Qt::CheckState ) value.toInt() ;
      standardItem->setCheckState( checkState ) ;
      emit CheckStateChanged( ( checkState == Qt::Checked ), standardItem->text() ) ;

      retval = true ;
   }

   return retval ;
}

CCheckableComboBox::CCheckableComboBox( QWidget * parent ) : QComboBox( parent )
{
   m_model = new CCheckableComboBoxModel( this ) ;
   setModel( m_model ) ;

   addItem( "Hello" ) ;
   addItem( "Bob" ) ;
}

CCheckableComboBox::~CCheckableComboBox()
{

}

[mrjj]

Hi
For the items, do you set
item->setData(Qt::Unchecked, Qt::CheckStateRole);
as else the state is undefined and it it might not render the checkbox or
something like that.

[HunterMetcalfe]

@mrjj hmmm so that would require me to overload the addItem function in QComboBox I don't think that's the ideal solution as the model should tell the view all of that information. In the past when I've added items to a QTableView/QListView, I've never had to do that for checkboxes. Since I've reimplemented the flags function it automatically sets all items added to have a CheckStateRole ( in the aforementioned views ) - or at least I thought it worked that way.

[mrjj]

@HunterMetcalfe
hi
Hmm i must agree since i used a QStandardItemModel
but you do have the flag function/custom model so
I would also assume that should be enough.

Is the code complete enough to run ?

[Christian Ehrlicher]

Please see also https://bugreports.qt.io/browse/QTBUG-60310