Please help with QTableWidget.

[chris_helloworld]

I have a QTableWidget that is populated and want to change the data in one of the cells. I do something like,

QTableWidgetItem *item = mytable->item(row, col);
item->setText("new data");

/* or item->setData(Qt:isplayRole, somevariant) */

However the QTableWidget is not correctly updated. Resizing the table or simply clicking in it, does cause the data to be correctly refreshed and shows the new value.

Is there something I need to do to tell QTableWidget that the data has been changed ?

Thanks in advance,
Chris.

[tbscope]

You could try:

update(indexFromItem(item));

update(indexFromItem(item));

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[Zlatomir]

You can use signals and slots: emit some signal whenever you change something, and call update or repaint

[chris_helloworld]

Thanks guys,
It tried
update(indexFromItem(item));

and also
repaint();

but neither of these approaches seemed to work

[tbscope]

That's weird.

Normally, you shouldn't even need to call update or repaint yourself as changing an item calls this internally.

And now you don't even see the updated item even if you directly call update or repaint. To me this sounds like the problem is somewhere else. Can you post the complete code please?

[Zlatomir]

I don't know what can be wrong with your code, but i can recommend an example: the code from 2nd Edition of C++ GUI Programming with Qt4 contains an example of a Spreadsheet maybe that code will help you correct the issue in your code (you can download the source code from the link)

[chris_helloworld]

Thanks,
I will try producing a small example app that reproduces the problem.

Cheers

[chris_helloworld]

The following code demos the problem.

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QtGui>
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    MainWindow(QWidget *parent = 0);
    QTableWidget *table;
    QPushButton *b1;
public slots:
    void inc();
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QtGui>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = 0);
    QTableWidget *table;
    QPushButton *b1;
public slots:
    void inc();
};

#endif // MAINWINDOW_H

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mainwindow.cpp

#include "mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    QVBoxLayout *l = new QVBoxLayout();
    table = new QTableWidget(1, 1);
    table->verticalHeader()->setDefaultSectionSize(16);
    table->verticalHeader()->hide();
 
    table->setItem(0, 0, new QTableWidgetItem("1"));
 
    b1 = new QPushButton("Increment");
 
    l->addWidget(table);
    l->addWidget(b1);
 
    QWidget *w = new QWidget();
    w->setLayout(l);
    setCentralWidget(w);
 
    connect(b1, SIGNAL(clicked()), this, SLOT(inc()));
}
 
void MainWindow::inc()
{
    QTableWidgetItem *i = table->item(0, 0);
    i->setText(QString::number(i->text().toInt() + 1));
}

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    QVBoxLayout *l = new QVBoxLayout();
    table = new QTableWidget(1, 1);
    table->verticalHeader()->setDefaultSectionSize(16);
    table->verticalHeader()->hide();

    table->setItem(0, 0, new QTableWidgetItem("1"));

    b1 = new QPushButton("Increment");

    l->addWidget(table);
    l->addWidget(b1);

    QWidget *w = new QWidget();
    w->setLayout(l);
    setCentralWidget(w);

    connect(b1, SIGNAL(clicked()), this, SLOT(inc()));
}

void MainWindow::inc()
{
    QTableWidgetItem *i = table->item(0, 0);
    i->setText(QString::number(i->text().toInt() + 1));
}

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Clicking the button should increment the value in the table, but doesnt until the table is clicked on or resized etc..

[Zlatomir]

That example code works fine on my system (win 7 x64), i can test it on ubuntu 10.4 and debian 5 a little later.

[chris_helloworld]

I'm on Win XP SP3 and using Qt 4.5.3

[Zlatomir]

I use Qt 4.6.3,
have you tried, to force the repainting of table?

connect(b1, SIGNAL(clicked()), table, SLOT(repaint()));

connect(b1, SIGNAL(clicked()), table, SLOT(repaint()));

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[chris_helloworld]

Yes, and also tried simply calling table->repaint() directly after setting the data.
Neither helps

Chris.

[Zlatomir]

Update Qt, it is a bug, resolved in the newer releases of Qt

[chris_helloworld]

Ok, many thanks for your help - dont suppose you have a reference or web link to any info on the bug ?

[chris_helloworld]

Ah, just realised you included the link, thanks again