rowCount() is calling for all the top level items

[prasad_N]

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.

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();
}

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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]

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

[prasad_N]

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]

Hi Any idea, why is this happening ?

[wysota]

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

[prasad_N]

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]

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]

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]

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]

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.

[prasad_N]

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.

yes, There is a delay in populating data (I have populated 30 million rows with column count > 10).

One more problem:
And rowCount() is calling for all top level items when I emit headerDataChanged() signal which leads to further delay in selecting item & changing header.
Item is not getting selected until header data changes. there is a considerable delay in changing header data after that only item is getting selected.
my post related to this issue : http://www.qtcentre.org/threads/6307...ure?highlight=

[wysota]

yes, There is a delay in populating data (I have populated 30 million rows with column count > 10).

Maybe you can populate the model in batches? I think you could use canFetchMore() && fetchMore() for the invalid model index.

One more problem:

And rowCount() is calling for all top level items when I emit headerDataChanged() signal which leads to further delay in selecting item & changing header.

Think how to avoid changing the header too often. You can always show a custom header instead of the default one.