QTreeView memory consumption

[eyeofhell]

Hello.

I'm testing QTreeView functionality right now, and i was amazed by one thing. It seems that QTreeView memory consumption depends on items count O_O. This is highly unusual, since model-view containers of such type only keeps track for items being displayed, and rest of items are in the model. I have written a following code with a simple model that holds no data and just reports that it has 10 millions items. With MFC, Windows API or .NET tree / list with such model will take no memory, since it will display only 10-20 visible elements and will request model for more upon scrolling / expanding items. But with Qt, such simple model results in ~300Mb memory consumtion. Increasing number of items will increase memory consumption. Maybe anyone can hint me what i'm doing wrong?

#include <QtGui/QApplication>
#include <QTreeView>
#include <QAbstractItemModel>
 
class CModel : public QAbstractItemModel
{
  public: QModelIndex index
  (
    int i_nRow,
    int i_nCol,
    const QModelIndex& i_oParent = QModelIndex()
  ) const
  {
    return createIndex( i_nRow, i_nCol, 0 );
  }
 
  public: QModelIndex parent
  (
    const QModelIndex& i_oInex
  ) const
  {
    return QModelIndex();
  }
 
  public: int rowCount
  (
    const QModelIndex& i_oParent = QModelIndex()
  ) const
  {
    return i_oParent.isValid() ? 0 : 1000 * 1000 * 10;
  }
 
  public: int columnCount
  (
    const QModelIndex& i_oParent = QModelIndex()
  ) const
  {
    return 1;
  }
 
  public: QVariant data
  (
    const QModelIndex& i_oIndex,
    int i_nRole = Qt::DisplayRole
  ) const
  {
    return Qt::DisplayRole == i_nRole ? QVariant( "1" ) : QVariant();
  }
};
 
int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  QTreeView oWnd;
  CModel oModel;
  oWnd.setUniformRowHeights( true );
  oWnd.setModel( & oModel );
  oWnd.show();
  return a.exec();
}

#include <QtGui/QApplication>
#include <QTreeView>
#include <QAbstractItemModel>

class CModel : public QAbstractItemModel
{
  public: QModelIndex index
  (
    int i_nRow,
    int i_nCol,
    const QModelIndex& i_oParent = QModelIndex()
  ) const
  {
    return createIndex( i_nRow, i_nCol, 0 );
  }

  public: QModelIndex parent
  (
    const QModelIndex& i_oInex
  ) const
  {
    return QModelIndex();
  }

  public: int rowCount
  (
    const QModelIndex& i_oParent = QModelIndex()
  ) const
  {
    return i_oParent.isValid() ? 0 : 1000 * 1000 * 10;
  }

  public: int columnCount
  (
    const QModelIndex& i_oParent = QModelIndex()
  ) const
  {
    return 1;
  }

  public: QVariant data
  (
    const QModelIndex& i_oIndex,
    int i_nRole = Qt::DisplayRole
  ) const
  {
    return Qt::DisplayRole == i_nRole ? QVariant( "1" ) : QVariant();
  }
};

int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  QTreeView oWnd;
  CModel oModel;
  oWnd.setUniformRowHeights( true );
  oWnd.setModel( & oModel );
  oWnd.show();
  return a.exec();
}

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[eyeofhell]

Bump. Still can't find out how to correctly use QAbstractItemModel + QTreeView in order to prevent gigabytes of memory consumption. Will appreciate any help.

[tbscope]

Can you explain how you measured the memory consumption?
Did you try the QStandardItemModel too?

[eyeofhell]

Memory consumption is measured via task manager . Run app without connected model = 20mb, run app with connected model = 320mb O_O.
As far as i understand, using QSTandardItemModel will effectively reduce QTreeView to QTreeWidget - i will not be able to supply data dynamically as needed. For SQL queries that can be millions of records this will be a bit slow .

[tbscope]

Memory measurement via the task manager is like asking a baby the yield of a certain nuclear bomb :-)
It doesn't tell you the real information you want.

Nevertheless I believe you when your program starts using more and more memory. I also enjoyed using the list and tree widgets of windows.

Your understanding that using QStandardItemModel will reduce QTreeView to QTreeWidget isn't correct. QTreeWidget manages the items itself. Using a QTreeView together with QStandardItemModel changes nothing. It's a standard view and a standard model.

For SQL queries I suggest you look into one of the QSql...Model classes. Try it first with one of these and see if you still get big memory consumptions.

For a personal project I need to display thousands of items from a database in a treeview, and the memory consumption is minimal.

[eyeofhell]

It seems that if i replace QTreeView with QTableView in my example code memory is not consumed anymore O_O. So it seems that QTreeView is just not intended to be used for very huge amounts of data and QTableView must be used instead.

[dw]

For a personal project I need to display thousands of items from a database in a treeview, and the memory consumption is minimal.

Then maybe you could help me with some ideas.

I also have a big QTreeView and its model gets the display data from an sqlite database. So when the tree is drawed 2 queries are executed per row to get the data. This gives the view an annoying delay (for scrolling, expanding a branch etc.). Also when I have the database in the memory. If I use any styling on it that doubles the delay.

Didn't you have this problem? Should I initialize the model by reading everything from the database and building a hierarchical structure to the memory? Any other idea to improve performance?