Selection synchronization of two tables (QTableView)

[mehmety888]

Hi,
I have two tables. (tableview1 and tableview2)
When I select a row(s) from left table, I want same row(s) to be selected at right table.
Similarly, when I select a row from right table I want same row to be selected at left table.

We are using a proxy model in both tables:

What we initially try to do is

tableview2->setModel(tableview1->model());
// hide columns ABD from tableview1
// hide columns CEFG from tableview2
tableview2->setSelectionModel(tableview1->selectionModel());

It does not work (maybe because of proxy model)

We try this connection:

connect(tableview1->selectionModel(), &QItemSelectionModel::selectionChanged,
            tableview2, &TableView::slotSelection1Changed);
connect(tableview2->selectionModel(), &QItemSelectionModel::selectionChanged,
            tableview1, &TableView::slotSelection2Changed);

we use the code section below:

tableview1->selectionModel()->select(index, QItemSelectionModel::Select | QItemSelectionModel::Rows);

However, it is very slow when we have 10000 rows. Do you have any idea how to solve this problem?

Many thanks,

[JonB]

@mehmety888
I have two observations, not solutions:

• tableview2->setSelectionModel(tableview1->selectionModel());: I don't think you're supposed to share a selection model this way? There are different physical selections going on for two views, so won't they need their own separate selection models?

• The paired connect()s: Don't know, and don't know whether this might cause your "slowness". Aren't you at least in danger of this setting off a "chain reaction", where each keeps changing something about the selection in the other, and then back again? I'd at least put a qDebug() in each slot to verify how often they are being called. Separately, 10,000 rows is a lot to show the user in an interactive table view, I wouldn't enjoy scrolling through them....

[mehmety888]

Hi JonB,

Thank you for your observations. For second observation, I am trying to prevent chain reaction below. However, it is called 5 times. Do you have suggestions to prevent this?

is_table1_selected = true;
tableview1->selectionModel()->blockSignals(true);
tableview1->selectionModel()->clearSelection();
if (false == is_table2_selected )
{
   for (QModelIndex index : in_model_index_list)
   {
       tableview1->selectionModel()->select(index, QItemSelectionModel::Select | QItemSelectionModel::Rows);
   }
}
tableview1->selectionModel()->blockSignals(false);
is_table1_selected = false;

[JonB]

@mehmety888
Yes, I did wonder. Don't know, your code looks reasonable. I'm not a great fan of using blockSignals(), to me it's like a mallet to crack a nut. Blocking all signals might lead to ignoring some signal which you do need being ignored. Having said that, if anything this should block too many signals, not too few.

I assume the code you show is duplicated for the other table. I also assume you are expecting just two invocations, one for each table, rather than 5. I would first verify I get just the one if I remove one table selecting the other. Then I would put qDebug() statements in, to figure what is going on. I would print out the QItemSelection arguments to selectionChanged() slot, so I could understand what is being selected/deselected. If necessary I would introduce a lambda to allow for an extra argument so that I could understand who is caller/callee/where/when. Standard debug-type techniques. Then I would fix as necessary :)

[mehmety888]

@JonB I debug my code and now it is called one time, performance is improved. However it is still very slow compared to single table selection.

I have found similar bug report like below.
https://bugreports.qt.io/browse/QTBUG-59478

[JonB]

@mehmety888

I debug my code and now it is called one time, performance is improved.

That at least is good.

You talk about single vs multi-table selection. However the bug report concerns

If programmatically select not consecutive rows in a very big tableview

First sort out whether your slowness is to do with non-consecutives in one table vs anything to do with two tables.

I also asked whether you're supposed to share a selection model across multiple views, but that does not seem to have been addressed.