rowCount() is calling for all the top level items

**prasad_N** · 8th July 2015, 19:07

Originally Posted by wysota

This example shows that the view does not query the whole model when it initializes:

Originally Posted by wysota

No, it's a default behaviour of QTreeView since the tree wants to know whether each of the items has child items:

these 2 statements are conflicting right ?

1. In my model rowCount is calling for all the top level items.

my model is :

Qt Code:

Switch view

QModelIndex TreeModel::index( int row, int column, const QModelIndex &parent ) const
{
    if ( ! hasIndex(row, column, parent) )
        return QModelIndex();
 
   TreeItem *parentItem;
 
    if ( ! parent.isValid() )
     parentItem = m_rootItem;
    else
     parentItem = static_cast<TreeItem*>( parent.internalPointer() );
 
    TreeItem *childItem = parentItem->child( row );
    if ( childItem )
     return createIndex( row, column, childItem );
    else
     return QModelIndex();
}
 
QModelIndex TreeModel::parent( const QModelIndex &index ) const
{
    if ( ! index.isValid() )
        return QModelIndex();
 
    TreeItem *childItem  = static_cast<TreeItem*>( index.internalPointer() );
    TreeItem *parentItem = childItem->parent();
 
    if ( (parentItem == m_rootItem)  || (parentItem == NULL))
        return QModelIndex();
 
    return createIndex( parentItem->row(), 0, parentItem );
}
 
int TreeModel::rowCount( const QModelIndex &parent ) const
{
       if ( parent.column() > 0 )
        return 0;
 
    TreeItem *parentItem;
    if ( ! parent.isValid() )
        parentItem = m_rootItem;
    else
        parentItem = static_cast<TreeItem*>( parent.internalPointer() );
 
    return parentItem->childCount();
}

QModelIndex TreeModel::index( int row, int column, const QModelIndex &parent ) const
{
    if ( ! hasIndex(row, column, parent) )
        return QModelIndex();

   TreeItem *parentItem;

    if ( ! parent.isValid() )
     parentItem = m_rootItem;
    else
     parentItem = static_cast<TreeItem*>( parent.internalPointer() );

    TreeItem *childItem = parentItem->child( row );
    if ( childItem )
     return createIndex( row, column, childItem );
    else
     return QModelIndex();
}

QModelIndex TreeModel::parent( const QModelIndex &index ) const
{
    if ( ! index.isValid() )
        return QModelIndex();

    TreeItem *childItem  = static_cast<TreeItem*>( index.internalPointer() );
    TreeItem *parentItem = childItem->parent();

    if ( (parentItem == m_rootItem)  || (parentItem == NULL))
        return QModelIndex();

    return createIndex( parentItem->row(), 0, parentItem );
}

int TreeModel::rowCount( const QModelIndex &parent ) const
{
       if ( parent.column() > 0 )
        return 0;

    TreeItem *parentItem;
    if ( ! parent.isValid() )
        parentItem = m_rootItem;
    else
        parentItem = static_cast<TreeItem*>( parent.internalPointer() );

    return parentItem->childCount();
}

To copy to clipboard, switch view to plain text mode

2. When I change your model little bit on order to check tree function calling. in the index if(parent.isValid()) is not at all executing.

Qt Code:

Switch view

int rowCount(const QModelIndex &parent = QModelIndex()) const {
    qDebug() << Q_FUNC_INFO << parent;
    if(parent.isValid()) return 2;    //each parent with 2 child
    return 10;                            // 10 top most parrents
  }
 
  QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const {
      if(parent.isValid()){        // this condition is not at all executing 
          qDebug() << "Yes isValid = " << parent.child(row, column);
          return createIndex(row, column, (void*)parent.child(row, column).internalPointer());   //create &return child index
      }
 
    return createIndex(row, column, (void*)0);    // return top most elements index's
  }

int rowCount(const QModelIndex &parent = QModelIndex()) const {
    qDebug() << Q_FUNC_INFO << parent;
    if(parent.isValid()) return 2;    //each parent with 2 child
    return 10;                            // 10 top most parrents
  }

  QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const {
      if(parent.isValid()){        // this condition is not at all executing 
          qDebug() << "Yes isValid = " << parent.child(row, column);
          return createIndex(row, column, (void*)parent.child(row, column).internalPointer());   //create &return child index
      }

    return createIndex(row, column, (void*)0);    // return top most elements index's
  }

To copy to clipboard, switch view to plain text mode

What wrong am I doing here ?

I don't want to use treeItems in my model for tree(if possible, I think it is possible with above implementation).

**wysota** · 8th July 2015, 20:13

Originally Posted by prasad_N

these 2 statements are conflicting right ?

Yes, I didn't express myself clearly. I meant that it is the view which is causing what you see, not the model. I didn't mean to say that "the view has to query all the indexes".

1. In my model rowCount is calling for all the top level items.

my model is :

Qt Code:

Switch view

QModelIndex TreeModel::index( int row, int column, const QModelIndex &parent ) const
{
    if ( ! hasIndex(row, column, parent) )
        return QModelIndex();
 
   TreeItem *parentItem;
 
    if ( ! parent.isValid() )
     parentItem = m_rootItem;
    else
     parentItem = static_cast<TreeItem*>( parent.internalPointer() );
 
    TreeItem *childItem = parentItem->child( row );
    if ( childItem )
     return createIndex( row, column, childItem );
    else
     return QModelIndex();
}
 
QModelIndex TreeModel::parent( const QModelIndex &index ) const
{
    if ( ! index.isValid() )
        return QModelIndex();
 
    TreeItem *childItem  = static_cast<TreeItem*>( index.internalPointer() );
    TreeItem *parentItem = childItem->parent();
 
    if ( (parentItem == m_rootItem)  || (parentItem == NULL))
        return QModelIndex();
 
    return createIndex( parentItem->row(), 0, parentItem );
}
 
int TreeModel::rowCount( const QModelIndex &parent ) const
{
       if ( parent.column() > 0 )
        return 0;
 
    TreeItem *parentItem;
    if ( ! parent.isValid() )
        parentItem = m_rootItem;
    else
        parentItem = static_cast<TreeItem*>( parent.internalPointer() );
 
    return parentItem->childCount();
}

QModelIndex TreeModel::index( int row, int column, const QModelIndex &parent ) const
{
    if ( ! hasIndex(row, column, parent) )
        return QModelIndex();

   TreeItem *parentItem;

    if ( ! parent.isValid() )
     parentItem = m_rootItem;
    else
     parentItem = static_cast<TreeItem*>( parent.internalPointer() );

    TreeItem *childItem = parentItem->child( row );
    if ( childItem )
     return createIndex( row, column, childItem );
    else
     return QModelIndex();
}

QModelIndex TreeModel::parent( const QModelIndex &index ) const
{
    if ( ! index.isValid() )
        return QModelIndex();

    TreeItem *childItem  = static_cast<TreeItem*>( index.internalPointer() );
    TreeItem *parentItem = childItem->parent();

    if ( (parentItem == m_rootItem)  || (parentItem == NULL))
        return QModelIndex();

    return createIndex( parentItem->row(), 0, parentItem );
}

int TreeModel::rowCount( const QModelIndex &parent ) const
{
       if ( parent.column() > 0 )
        return 0;

    TreeItem *parentItem;
    if ( ! parent.isValid() )
        parentItem = m_rootItem;
    else
        parentItem = static_cast<TreeItem*>( parent.internalPointer() );

    return parentItem->childCount();
}

To copy to clipboard, switch view to plain text mode

This is the implementation of QAbstractItemModel::hasIndex():

Qt Code:

Switch view

bool QAbstractItemModel::hasIndex(int row, int column, const QModelIndex &parent) const
{
    if (row < 0 || column < 0)
        return false;
    return row < rowCount(parent) && column < columnCount(parent);
}

bool QAbstractItemModel::hasIndex(int row, int column, const QModelIndex &parent) const
{
    if (row < 0 || column < 0)
        return false;
    return row < rowCount(parent) && column < columnCount(parent);
}

To copy to clipboard, switch view to plain text mode

Therefore each time you call you index() implementation, it calls hasIndex() which in turn calls rowCount() for the parent. Possibly this applies to other methods and their default implementations.

2. When I change your model little bit on order to check tree function calling. in the index if(parent.isValid()) is not at all executing.

Qt Code:

Switch view

int rowCount(const QModelIndex &parent = QModelIndex()) const {
    qDebug() << Q_FUNC_INFO << parent;
    if(parent.isValid()) return 2;    //each parent with 2 child
    return 10;                            // 10 top most parrents
  }
 
  QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const {
      if(parent.isValid()){        // this condition is not at all executing 
          qDebug() << "Yes isValid = " << parent.child(row, column);
          return createIndex(row, column, (void*)parent.child(row, column).internalPointer());   //create &return child index
      }
 
    return createIndex(row, column, (void*)0);    // return top most elements index's
  }

int rowCount(const QModelIndex &parent = QModelIndex()) const {
    qDebug() << Q_FUNC_INFO << parent;
    if(parent.isValid()) return 2;    //each parent with 2 child
    return 10;                            // 10 top most parrents
  }

  QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const {
      if(parent.isValid()){        // this condition is not at all executing 
          qDebug() << "Yes isValid = " << parent.child(row, column);
          return createIndex(row, column, (void*)parent.child(row, column).internalPointer());   //create &return child index
      }

    return createIndex(row, column, (void*)0);    // return top most elements index's
  }

To copy to clipboard, switch view to plain text mode

What wrong am I doing here ?

Most likely you didn't change the base class to QAbstractItemModel. Apparently QTreeView has an optimization to not check child nodes for flat models.

Qt Code:

Switch view

#include <QtWidgets>
 
#define BASEMODEL QAbstractItemModel
 
class Model : public BASEMODEL {
public:
  Model(QObject *parent = 0) : BASEMODEL(parent) {}
 
  int columnCount(const QModelIndex &parent = QModelIndex()) const { return 1; }
 
  int rowCount(const QModelIndex &parent = QModelIndex()) const {
    qDebug() << Q_FUNC_INFO << parent;
    if(!parent.isValid()) return 10;
    if(parent.isValid() && !parent.parent().isValid()) return 2; // limit to two levels
 
    return 0;
  }
  QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const {
    qDebug() << Q_FUNC_INFO << row << column << parent;
    if(parent.isValid()) {
	qDebug() << Q_FUNC_INFO << "parent valid";
	// we only need id of the parent since it identifies the item
	return createIndex(row, column, parent.row());
    }
    return createIndex(row, column, -1); // top level item has invalid parent
  }
 
  QModelIndex parent(const QModelIndex &ind) const {
    qDebug() << Q_FUNC_INFO << ind;
    if(!ind.isValid()) return QModelIndex();
    int id = ind.internalId();
    if( id == -1) return QModelIndex();
    return index(id, 0); // return top-level item
  }
 
  QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const {
    if(role == Qt::DisplayRole) return index.row()+1;
    return QVariant();
  }
};
 
int main(int argc, char **argv) {
  QApplication app(argc, argv);
  QTreeView v;
  Model model;
  v.setModel(&model);
  v.show();
  return app.exec();
}

#include <QtWidgets>

#define BASEMODEL QAbstractItemModel

class Model : public BASEMODEL {
public:
  Model(QObject *parent = 0) : BASEMODEL(parent) {}

  int columnCount(const QModelIndex &parent = QModelIndex()) const { return 1; }
  
  int rowCount(const QModelIndex &parent = QModelIndex()) const {
    qDebug() << Q_FUNC_INFO << parent;
    if(!parent.isValid()) return 10;
    if(parent.isValid() && !parent.parent().isValid()) return 2; // limit to two levels
    
    return 0;
  }
  QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const {
    qDebug() << Q_FUNC_INFO << row << column << parent;
    if(parent.isValid()) {
	qDebug() << Q_FUNC_INFO << "parent valid";
	// we only need id of the parent since it identifies the item
	return createIndex(row, column, parent.row());
    }
    return createIndex(row, column, -1); // top level item has invalid parent
  }

  QModelIndex parent(const QModelIndex &ind) const {
    qDebug() << Q_FUNC_INFO << ind;
    if(!ind.isValid()) return QModelIndex();
    int id = ind.internalId();
    if( id == -1) return QModelIndex();
    return index(id, 0); // return top-level item
  }
  
  QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const {
    if(role == Qt::DisplayRole) return index.row()+1;
    return QVariant();
  }
};

int main(int argc, char **argv) {
  QApplication app(argc, argv);
  QTreeView v;
  Model model;
  v.setModel(&model);
  v.show();
  return app.exec();
}

To copy to clipboard, switch view to plain text mode

I don't want to use treeItems in my model for tree(if possible, I think it is possible with above implementation).

Then don't use them

By the way, changing the base class to QAbstractItemModel does cause the tree view to query rowCount for all the top-level items at start, I will try to see why this happens. You can probably switch some property and it will stop doing that.

Edit: It looks like during layout of the tree, the widget calls rowCount() on items that have children. What is worrying is that it also calls canFetchMore() && fetchMore() for them which in my opinion defeats the purpose of implementing those two methods at all at least for two level models.

**prasad_N** · 9th July 2015, 06:28

but when I test your new model I have seen all the top levels items rowsCount() is getting called, I am struggling exactly with this behavior only.

Qt Code:

Switch view

int rowCount(const QModelIndex &parent = QModelIndex()) const 
{
      qDebug() << parent;   //little change in debug msg
 
    if(!parent.isValid()) return 10;
    if(parent.isValid() && !parent.parent().isValid()) return 2; // limit to two levels
 
    return 0;
  }
 
int main(int argc, char **argv) {
  QApplication app(argc, argv);
  QTreeView v; 
  v.setFixedSize(200, 50);  //set height to 50 so that view can accommodate 2 top level elements only 
  Model model;
  v.setModel(&model);
  v.show();
  return app.exec();
}

int rowCount(const QModelIndex &parent = QModelIndex()) const 
{
      qDebug() << parent;   //little change in debug msg

    if(!parent.isValid()) return 10;
    if(parent.isValid() && !parent.parent().isValid()) return 2; // limit to two levels

    return 0;
  }

int main(int argc, char **argv) {
  QApplication app(argc, argv);
  QTreeView v; 
  v.setFixedSize(200, 50);  //set height to 50 so that view can accommodate 2 top level elements only 
  Model model;
  v.setModel(&model);
  v.show();
  return app.exec();
}

To copy to clipboard, switch view to plain text mode

The out put I observed is :

QModelIndex(-1,-1,0x0,QObject(0x0) )
QModelIndex(-1,-1,0x0,QObject(0x0) )
QModelIndex(-1,-1,0x0,QObject(0x0) )
QModelIndex(0,0,0xffffffff,QAbstractItemModel(0x28 fe18) )
QModelIndex(1,0,0xffffffff,QAbstractItemModel(0x28 fe18) )
QModelIndex(2,0,0xffffffff,QAbstractItemModel(0x28 fe18) )
QModelIndex(3,0,0xffffffff,QAbstractItemModel(0x28 fe18) )
QModelIndex(4,0,0xffffffff,QAbstractItemModel(0x28 fe18) )
QModelIndex(5,0,0xffffffff,QAbstractItemModel(0x28 fe18) )
QModelIndex(6,0,0xffffffff,QAbstractItemModel(0x28 fe18) )
QModelIndex(7,0,0xffffffff,QAbstractItemModel(0x28 fe18) )
QModelIndex(8,0,0xffffffff,QAbstractItemModel(0x28 fe18) )
QModelIndex(9,0,0xffffffff,QAbstractItemModel(0x28 fe18) )

//rowCount() is getting called for all top level items here.

One more thing I have observed is, When i return 10000000(top level items) in rowCount() (in old model you suggested & in new model also), My application got crashed with runtime error (on Windows 8, 64bit application).
And when I return 1000000 row count & when I try to scroll down its hanging like hell, not able to scroll at all.

**wysota** · 9th July 2015, 08:36

Which Qt version are you using? How much RAM does your machine have?

**prasad_N** · 9th July 2015, 09:01

I am using 4.8.6 & 5.4.0 with windows 8 and 4GB RAM, I tested on both the versions it failed.

**prasad_N** · 9th July 2015, 20:18

Hi Any idea, why is this happening ?

**wysota** · 9th July 2015, 21:06

4E9 bytes for 1E7 items yields 4E2 (=400) bytes per item. My guess is you are running out of memory

**prasad_N** · 10th July 2015, 07:49

No I am not, It is taking around 128MB (for 10000000 top level items) && 28MB (for 1000000 top level items).
still view is freezing like anything when I scroll, did you reproduce same when you pass more top level count.

**wysota** · 10th July 2015, 08:16

If you call setUniformRowHeights(true) then there is no such effect. I can scroll the view very quickly.

By the way, I don't think you calculated the memory use correctly. For 10M top-level items with 2 child items each the application uses over 600MB for the data segment.

**prasad_N** · 10th July 2015, 08:56

Originally Posted by wysota

If you call setUniformRowHeights(true) then there is no such effect. I can scroll the view very quickly.

- forgot to set setUniformRowHeights(true), Its working fine now

- The only & main issue I have now is, rowCount() is still calling for all the top level items , Any idea how to prevent it.?

By the way, I don't think you calculated the memory use correctly. For 10M top-level items with 2 child items each the application uses over 600MB for the data segment.

Sorry I ran 32-bit application, It is taking around 280MB in a same case.

**prasad_N** · 11th July 2015, 20:36

Hi Wysota,
Did you find any solution for this (rowCount() is calling for all the top level items),
I have observed one more thing that "Even for each mouse click on cell is calling rowCount() for all the top level items"
I think this is the reason for my recent post - http://www.qtcentre.org/threads/6307...ure?highlight=

what kind of optimizations we can do for both the problems.

**wysota** · 11th July 2015, 23:39

Why is that a problem that the framework calls rowCount() of every top-level item? Do you get noticable slowdowns because of that? The only "solution" I can see is to file a bug.

Thread: rowCount() is calling for all the top level items

Thread Tools

Search Thread

Display

Hybrid View

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Re: rowCount() is calling for all the top level items

Similar Threads

filterAcceptRows() is being called for all the top level items in the tree.

How to stop calling data() function for the child items in a tree view initially

how to prevent child QGraphicItem from picking when calling items(path)?

QTreeWidget::findItems only searches top level items ?

Force a QDialog to be the top-level Window and to stay at this level ?

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions