rowCount() is calling for all the top level items

[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.

[prasad_N]

Sorry I could not get you properly.

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

You mean populating model with half data.
Actually I have more than 100 million of rows (would be more also) because of this BUG (https://bugreports.qt.io/browse/QTBUG-28631), I went for pages (I will have combo box top of the view with 0 - totalRows/30 million ranges), so each time I chose a number I am building a tree of respective range and showing that tree so that I am showing 30 million of rows at a time in view, but this is also causing performance problems.

with fetchMore() & canFetchMore() i will have scroll bar problem I think, when I come to end of the scroll then only I would come to know there is more elements and then I will load the data and then the scroll bar will adjust according to that, I don't want this behavior scroll bar size should be decide at first instance only(This is the reason I am not using fetchMore functionality in my app).

One more problem:

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

You mean, you want me to customize the header also ?


Can you be more verbose for the above 2 statements :-)

[wysota]

You mean populating model with half data.

I mean populate as much as is currently useful for you. If the user scrolls down, populate more, etc.

with fetchMore() & canFetchMore() i will have scroll bar problem I think, when I come to end of the scroll then only I would come to know there is more elements and then I will load the data and then the scroll bar will adjust according to that, I don't want this behavior scroll bar size should be decide at first instance only(This is the reason I am not using fetchMore functionality in my app).

You are out of luck then You can file a bug or provide a patch for the (IMO incorrect) behaviour.

You mean, you want me to customize the header also ?


Can you be more verbose for the above 2 statements :-)

You can hide the original header and replace it with your own instance of QHeaderView that is not tied to the model as I understand you want your header to reflect the current view state rather than the model's data.

[prasad_N]

I report a bug in Qt bug tracker for this.

You can hide the original header and replace it with your own instance of QHeaderView that is not tied to the model as I understand you want your header to reflect the current view state rather than the model's data.

I want my header to be changed depends on the row I clicked (for ex: if I click on a even row (index.row()%2 == 0 ) I put one header set & for odd row I put another header set).
in this case how a customized header can help me ?
And I could not see any function for setting data (if I customize QHeaderView) rather than QHeaderView::setRootIndex(QModelIndex);

Thanks.

[wysota]

The header takes its data from headerData() method of the model. Simply provide a custom model for it. It can even be empty just make it return whatever you need from headerData().

[prasad_N]

The header takes its data from headerData() method of the model. Simply provide a custom model for it. It can even be empty just make it return whatever you need from headerData().

Thanks, It did worked with the sample I provided here, need to check with my project hope will work :-)