QTableWidget::setItem very slow the second time

[miraks]

Hi all,

I am trying to populate a QTableWidget with 50 lines and 50 columns with the following code:

{
        SKGTRACEIN(10, "test-Filltable");
        ui.kTable->clear();
        ui.kTable->setRowCount(50);
        ui.kTable->setColumnCount(50);
        for (int i=0; i<49; ++i) {
                for (int j=0; j<49; ++j) {
                        SKGTRACEIN(10, "test-setItem");
                        QTableWidgetItem* item=new QTableWidgetItem("A");
                        ui.kTable->setItem(i, j, item);
                }
        }
}

{
        SKGTRACEIN(10, "test-Filltable");
        ui.kTable->clear();
        ui.kTable->setRowCount(50);
        ui.kTable->setColumnCount(50);
        for (int i=0; i<49; ++i) {
                for (int j=0; j<49; ++j) {
                        SKGTRACEIN(10, "test-setItem");
                        QTableWidgetItem* item=new QTableWidgetItem("A");
                        ui.kTable->setItem(i, j, item);
                }
        }
}

To copy to clipboard, switch view to plain text mode 

The macro SKGTRACEIN allows to measure the time consumed by the code in of the scope.

The first call of the code returns following traces:

##    >test-Filltable
##      >test-setItem
##      <test-setItem TIME=0.100014 ms
##      >test-setItem
##      <test-setItem TIME=0.0169843 ms
##      >test-setItem
##      <test-setItem TIME=0.0140117 ms
##      >test-setItem
##      <test-setItem TIME=0.0148984 ms
##      >test-setItem
##      <test-setItem TIME=0.0140293 ms
...
...
##      >test-setItem
##      <test-setItem TIME=0.0139316 ms
##      >test-setItem
##      <test-setItem TIME=0.0148886 ms
##      >test-setItem
##      <test-setItem TIME=0.0138925 ms
##      >test-setItem
##      <test-setItem TIME=0.0150938 ms
##      >test-setItem
##      <test-setItem TIME=0.0150508 ms
##    <test-Filltable TIME=431.761 ms

##    >test-Filltable
##      >test-setItem
##      <test-setItem TIME=0.100014 ms
##      >test-setItem
##      <test-setItem TIME=0.0169843 ms
##      >test-setItem
##      <test-setItem TIME=0.0140117 ms
##      >test-setItem
##      <test-setItem TIME=0.0148984 ms
##      >test-setItem
##      <test-setItem TIME=0.0140293 ms
...
...
##      >test-setItem
##      <test-setItem TIME=0.0139316 ms
##      >test-setItem
##      <test-setItem TIME=0.0148886 ms
##      >test-setItem
##      <test-setItem TIME=0.0138925 ms
##      >test-setItem
##      <test-setItem TIME=0.0150938 ms
##      >test-setItem
##      <test-setItem TIME=0.0150508 ms
##    <test-Filltable TIME=431.761 ms

To copy to clipboard, switch view to plain text mode 

As you can see, performances are very good. Table is done in around 431ms.

The second call of this same code returns following traces:

##    >test-Filltable
##      >test-setItem
##      <test-setItem TIME=27.6061 ms
##      >test-setItem
##      <test-setItem TIME=13.549 ms
##      >test-setItem
##      <test-setItem TIME=14.058 ms
##      >test-setItem
##      <test-setItem TIME=14.132 ms
##      >test-setItem
##      <test-setItem TIME=13.943 ms
...
...
##      <test-setItem TIME=77.392 ms
##      >test-setItem
##      <test-setItem TIME=133.818 ms
##      >test-setItem
##      <test-setItem TIME=89.083 ms
##      >test-setItem
##      <test-setItem TIME=60.1529 ms
##      >test-setItem
##      <test-setItem TIME=61.99 ms
##    <test-Filltable TIME=109696 ms

##    >test-Filltable
##      >test-setItem
##      <test-setItem TIME=27.6061 ms
##      >test-setItem
##      <test-setItem TIME=13.549 ms
##      >test-setItem
##      <test-setItem TIME=14.058 ms
##      >test-setItem
##      <test-setItem TIME=14.132 ms
##      >test-setItem
##      <test-setItem TIME=13.943 ms
...
...
##      <test-setItem TIME=77.392 ms
##      >test-setItem
##      <test-setItem TIME=133.818 ms
##      >test-setItem
##      <test-setItem TIME=89.083 ms
##      >test-setItem
##      <test-setItem TIME=60.1529 ms
##      >test-setItem
##      <test-setItem TIME=61.99 ms
##    <test-Filltable TIME=109696 ms

To copy to clipboard, switch view to plain text mode 

Now, performances are very bad (+25000%) and it seems to be due to setItem.

Why ? What is the solution to have good performances each time ?

Thank you in advance for your help.

[jacek]

What happens if you add ui.kTable->setUpdatesEnabled( ... ) around that loop? If you are concerned about the performance, use QTableView and custom model.

[miraks]

What happens if you add ui.kTable->setUpdatesEnabled( ... ) around that loop? If you are concerned about the performance, use QTableView and custom model.

Hi Jacek,

I didn't know this method, so thank you very much, it's interesting.

But, I still have the same issue with this code:

{
                                                SKGTRACEIN(10, "test-Filltable");
                                                ui.kTable->setUpdatesEnabled(false);
                                                ui.kTable->clear();
                                                ui.kTable->setRowCount(50);
                                                ui.kTable->setColumnCount(50);
                                                for (int i=0; i<49; ++i) {
                                                        for (int j=0; j<49; ++j) {
                                                                SKGTRACEIN(10, "test-setItem");
                                                                QTableWidgetItem* item=new QTableWidgetItem("A");
                                                                ui.kTable->setItem(i, j, item);
                                                        }
                                                }
                                                ui.kTable->setUpdatesEnabled(true);
                                        }

{
                                                SKGTRACEIN(10, "test-Filltable");
                                                ui.kTable->setUpdatesEnabled(false);
                                                ui.kTable->clear();
                                                ui.kTable->setRowCount(50);
                                                ui.kTable->setColumnCount(50);
                                                for (int i=0; i<49; ++i) {
                                                        for (int j=0; j<49; ++j) {
                                                                SKGTRACEIN(10, "test-setItem");
                                                                QTableWidgetItem* item=new QTableWidgetItem("A");
                                                                ui.kTable->setItem(i, j, item);
                                                        }
                                                }
                                                ui.kTable->setUpdatesEnabled(true);
                                        }

To copy to clipboard, switch view to plain text mode 

I knows that I can use QTableView, but I don't want to do it each time I have a small table to display.
I did an example with 50*50 items but it's also true with 10*10 items.
I would like to understand why.

If you have an other idea ...

[miraks]

Hi Jacek,

I found the solution thanks to you.

I hide the table before modification, and I show it after:

{
                                                SKGTRACEIN(10, "test-Filltable");
                                                ui.kTable->hide();
                                                ui.kTable->clear();
                                                ui.kTable->setRowCount(10);
                                                ui.kTable->setColumnCount(10);
                                                for (int i=0; i<9; ++i) {
                                                        for (int j=0; j<9; ++j) {
                                                                SKGTRACEIN(10, "test-setItem");
                                                                QTableWidgetItem* item=new QTableWidgetItem("A");
                                                                ui.kTable->setItem(i, j, item);
                                                        }
                                                }
                                                ui.kTable->show();
                                        }

{
                                                SKGTRACEIN(10, "test-Filltable");
                                                ui.kTable->hide();
                                                ui.kTable->clear();
                                                ui.kTable->setRowCount(10);
                                                ui.kTable->setColumnCount(10);
                                                for (int i=0; i<9; ++i) {
                                                        for (int j=0; j<9; ++j) {
                                                                SKGTRACEIN(10, "test-setItem");
                                                                QTableWidgetItem* item=new QTableWidgetItem("A");
                                                                ui.kTable->setItem(i, j, item);
                                                        }
                                                }
                                                ui.kTable->show();
                                        }

To copy to clipboard, switch view to plain text mode 

With this, I always have the same performances.

Is it a bug ?

Sorry, I don't understand why, but I am not able to modify the title of my fist post to set [SOLVED].

[miraks]

I have a solution for a QTableWidget (hide + show), but do you know if we can have bad performances on QTableView too ?