Subclass QAbstractListModel - count issue

DeltaSim

Hello,

I have an issue using subclass of QAbstractListModel.
I want to use a custom model in a standard QML ListView.
The data is correctly updated but if the row size changed, the size of the listview doesn't change.

Here is my code (simplified):
QML

ListView{
   id: rectangleListMenu
   anchors.fill: parent
   clip: true
   interactive: height < contentHeight
   ScrollBar.vertical: ScrollBar {
                              id: scrollBar
                              policy: rectangleListMenu.interactive?ScrollBar.AlwaysOn:ScrollBar.AlwaysOff
                           }
   
   model: g_rectangleModel

   delegate: Rectangle{
      width: rectangleListMenu.width - (rectangleListMenu.interactive ? (scrollBar.width + rectangleListMenu.anchors.margins) : 0)
      height: rectangleListMenu.itemHeight
      color: s_recColor
   }
}

rectangleModel.h

class RectangleModel: public QAbstractListModel
{
   Q_OBJECT

public:

   enum RectangleModelRoles{
      RectangleColorRole = Qt::UserRole + 1
   };

   explicit RectangleModel(QObject *op_parent = nullptr);
   ~RectangleModel();

   int rowCount(const QModelIndex &parent = QModelIndex()) const override;
   QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
   QHash<int, QByteArray> roleNames() const override;

   void gv_updateRectangleList(QList<QString*> newRectangleColorList);


private:
   QList<QString*> m_rectangleColorList;
};

rectangleModel.cpp

#include "rectangleModel.h"

RectangleModel::RectangleModel(QObject *op_parent)
{
   Q_UNUSED(op_parent)
}

int RectangleModel::rowCount(const QModelIndex &parent) const
{
   Q_UNUSED(parent)

   return m_rectangleColorList.length();
}

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

   if(index.row() >= m_rectangleColorList.length())
   {
      return QVariant();
   }

   switch(role)
   {
   case(RectangleColorRole):
      return m_rectangleColorList.at(index.row());
      break;
   default:
      return QVariant();
      break;
   }
}


QHash<int, QByteArray> RectangleModel::roleNames() const
{

   static QHash<int, QByteArray> mapping{
      {RectangleColorRole, "s_recColor"},
   };
   return mapping;
}


void RectangleModel::gv_updateRectangleList(QList<QString*> newRectangleColorList)
{
   m_rectangleColorList = newRectangleColorList;
   
   const QModelIndex startIndex = index(0,0);
   const QModelIndex stopIndex = index(m_rectangleColorList.size()-1,0);
   emit dataChanged(startIndex,stopIndex);
}

RectangleModel::~RectangleModel(){}

I tried multiple things:

Adding a count Q_PROPERTY with countChanged signal
Removing rows and emitting beginRemoveRows and endRemoveRows then add new rows with related signals
Emitting layoutChanged
But without any success...

Thanks for your help.

sierdzio

You are returning wrong count in rowCount() - it should be the size of m_rectangleColorList but you return size of m_closeParcelList (different variable).

When changing items you absolutely should use begin...() and end...() methods, without them the ListView will not know that anything has changed.

DeltaSim

Yes, sorry about the rowCount I made a mistake in this code example, on my real program it is the righ array (I edited the post).
Wich begin... end... methiod should I call, I tried all of it without any success.

sierdzio

@DeltaSim said in Subclass QAbstractListModel - count issue:

RectangleModel::gv_updateRectangleList(QList<QString*> newRectangleColorList)

IN this method, you are replacing all items, so you should call:

beginResetModel();
m_rectangleColorList = newRectangleColorList;
endResetModel();

DeltaSim

@sierdzio thanks for your feedback.

I tried to emit those signals but the list size still doesn't change and I have this error:

QObject::connect: Cannot queue arguments of type 'QQmlChangeSet'
(Make sure 'QQmlChangeSet' is registered using qRegisterMetaType().)

sierdzio

They are not signals.

I don't think QML can handle a pointer to QString. Try changing your data to a QStringList.

Also, your constructor does not initialize the base class. This is very likely the root cause of your troubles.

RectangleModel::RectangleModel(QObject *op_parent) : QAbstractListModel(parent)
{
}

Regarding the error:

QObject::connect: Cannot queue arguments of type 'QQmlChangeSet'

I don't know where it comes from, the code you shared does not seem to try to do anything QQmlChangeSet.

DeltaSim

Ok I created a small project with only this part using resetModel functions and it works.
The problem is actually a thread problem.
The function "gv_updateRectangleList" is called in another tread this is why I have the QQmlChangeSet... error.

On main.ccp I create the model and the thread

RectangleModel * p_rectangleModel = new RectangleModel();
DummyThread *p_dummyThread = new DummyThread(p_rectangleModel);
p_dummyThread->start();

And on the run I call the update function, example:

void DummyThread::run()
{
   QList<QString*> rectList;

   while(true)
   {
      rectList.clear();

      if(msn_rectCount < 20)
      {
         msn_rectCount++;
      }
      else
      {
         msn_rectCount = 1;
      }

      for(int i=0; i<msn_rectCount; i++)
      {
         QString *s_string = new QString("#0000FF");
         rectList.push_back(s_string);
      }

      mp_rectangleModel->gv_updateRectangleList(rectList);

      sleep(3);
   }
}

sierdzio

Use signals and slots to communicate between threads, then it won't cause you any problems.

DeltaSim

Ok thank you it works.