Problem with number of lines in a layout

devarde

I am doing a simple program. Basically it reads a image and show how many different colors have the image. For each color it is added a QLabel and a QPushButton in a QHBoxLayout. This QHBoxLayout it is added to a QVBoxLayout. Though, when there are more than 234 colors the layout freezes. I replaced this several layouts by a GridLayout and the problems remains.
A curious fact is that a single column more than 234 QLabels doesn't generate any problem, but a single column with more than 234 QPushButton does generate.
Follow a brief excerpt of the code region where the problem happens:

for(int index = 0; index < numColors; index++)
        {
//            if( index == 230 ) return;
            QLabel *rgbLabel = new QLabel(QString("Color %1").arg(index));
            QPushButton *colorButton = new QPushButton( "..." );

            ui->gridLayoutColors->addWidget(rgbLabel, index, 0);
            ui->gridLayoutColors->addWidget(colorButton, index, 1);
        }

And so does it follows a screenshot with the problem

I forgot to mention my environment:

Ubuntu 14.04 LTS 64 bits (4 GB RAM)
i3 2 core,
Qt 4.8.6
gcc 4.8

Does someone know why this problem is happening? How I can circumvent it?

Obs: I have tested the project on the same machine but in a Win7 64 bits with Qt 4.8.6 + MSV2013 that I also have installed and everything worked OK. The test was done with a image containing 300 different colors. I believe it is a bug/limitation of Qt 4.8.6 for Linux.

Thanks beforehand.

SGaist

Hi,

Not an answer to your question but since your images number of colors might get way higher than that, shouldn't your rather use a QListView/QTableView + QStandardItemModel or a QListWidget/QTableWidget to show the text and maybe a custom QStyledItemDelegate to show the button when appropriate ?

devarde

It was what I did.

But I confess that I didn't hope that an error like that would happen. Though I imagine that it is due to it was not designed to a great number of child widgets, what makes sense.

VRonin

You should use a QListView/QTableView for this kind of things but just for the sake of it, this code runs fine for me (Qt 5.5 Windows 7)

#include <QApplication>
#include <QWidget>
#include <QDebug>
#include <QGridLayout>
#include <QPushButton>
#include <QLabel>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QWidget w;
    QGridLayout* gridLayoutColors=new QGridLayout(&w);
    for(int index = 0; index < 250; index++){

        QLabel *rgbLabel = new QLabel(QString("Color %1").arg(index),&w);
        QPushButton *colorButton = new QPushButton( "...",&w );

        gridLayoutColors->addWidget(rgbLabel, index, 0);
        gridLayoutColors->addWidget(colorButton, index, 1);
    }
    w.show();
    return a.exec();
}