[Solved]How to retrieve data from the QTableWidget ?

mahmoud899

Hello, I am a beginner in the Qt world. I have written a very simple program. In the program I have a button and a label, the label is set to the number 0. I want when I push the button the label to be reset to another number. I have written the following code
@
#include <QApplication>
#include <QLabel>
#include <QPushButton>
#include <QGridLayout>

void change( QLabel *label )
{
label->setText(QString::number('32'));
}

int main(int argc, char *argv[])
{
QApplication a(argc, argv);

QWidget *window = new QWidget;

QGridLayout *layout = new QGridLayout(window);

QPushButton *button = new QPushButton("+");
QLabel *value = new QLabel("0");

layout->addWidget(button);
layout->addWidget(value);

QObject::connect(button, SIGNAL(clicked()), value, SLOT(change(label)));

window->resize(200,200);
window->setWindowTitle("Project");
window->show();

return a.exec(&#41;;

}
@

When I run the code and press the push button nothing happens. Any suggestions how I fix that code. Please keep it simple as possible nothing fancy.

Thank You

mahmoud899

Small change in the code, instead of @SLOT(change(label))@

use this code
@SLOT(change(value))@

melghawi

Hello and welcome to Qt.

The reason why nothing happens is because you are connecting the button's clicked signal to the value's change slot which is not defined as a slot for the QLabel. Have a look at "this":http://qt-project.org/doc/qt-4.8/signalsandslots.html.

But basically you need to do something like this:

@
class CustomLabel : public QLabel
{
Q_OBJECT
public slots:
void change()
{
setText(QString::number('32'));
}
}
@

Then in your main.cpp you need to do something like this:

@
int main(int argc, char *argv[])
{
QApplication a(argc, argv);

QWidget *window = new QWidget;

QGridLayout *layout = new QGridLayout(window);

QPushButton *button = new QPushButton("+");
CustomLabel *value = new CustomLabel("0");

layout->addWidget(button);
layout->addWidget(value);

QObject::connect(button, SIGNAL(clicked()), value, SLOT(change()));

window->resize(200,200);
window->setWindowTitle("Project");
window->show();

return a.exec&#40;&#41;;

}
@

Now the value object has a change slot defined.

mahmoud899

communication.h
@
#ifndef COMMUNICATION_H
#define COMMUNICATION_H

#include <QApplication>
#include <QPushButton>
#include <QLabel>
#include <QWidget>

class myWindow : public QWidget
{
Q_OBJECT

public:
myWindow(QWidget *parent = 0);

private slots:
void onChange();

private:
QLabel *label;
};

#endif // COMMUNICATION_H
@

communication.cpp
@
#include "communication.h"

myWindow::myWindow(QWidget *parent)
:QWidget(parent)
{
QPushButton *button = new QPushButton("Change", this);
button->setGeometry(40,40,40,40);

label = new QLabel("0", this);
label->setGeometry(30,40,30,40);

connect(button, SIGNAL(clicked()), this, SLOT(change()));

}

void myWindow::onChange()
{
label->setText("Hello World");
}
@

main.cpp
@
QApplication a(argc, argv);

myWindow window;

myWindow.setWindowTitle("Communicate");
myWindow.show();

return a.exec();
@

I have written this code just to change a QLabel with a QPushButton. Now I have 2 questions,

1)When I run that code on Ubuntu Linux I get the following error:
"undefined reference to 'vtable for myWindow' and when I run it on Windows XP I don't get any errors and the program executes fine. How can I solve that problem on Ubuntu Linux?

The second question is, isn't there any other simple code to change a QLabel with a QPushButton?

Please put in mind that I am a beginner, so please keep your answers as simple as you can.

Thank You

SGaist

Hi,

For question 1: rerun qmake, or simply do a complete rebuild of your project. This is generally an error coming from add Q_OBJECT after having built the class one time.

It's already a simple way of doing what you want. The only other is to add the slot to derived QLabel class

Hope it helps

mahmoud899

For the problem that I have been having, building my project and an error occurs, I have rebuild the whole project and run qmake again and everything worked fine.

Thank You

SGaist

You're welcome,

Since it's all good now, don't forget to update the thread's title to solved so other forum users may also know :)

mahmoud899

Hello I have a couple of questions.

When I want to post a new question do I start a new thread or continue on the thread I have created?
When my problem is solved, how can I change the threads title to solved?
I am experimenting with QTableWidget. I have made a QTableWidget and I have inserted into one of the cells a number. Now I want to retrieve what is in the cell?

@
#include <QApplication>
#include <QHBoxLayout>
#include <QTableWidget>
#include <QTextStream>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);

QWidget window;
QTableWidgetItem *itemInTable;
QTextStream output(stdout);

QTableWidget *table = new QTableWidget(20,20);

QHBoxLayout *layout = new QHBoxLayout(&window);

layout->addWidget(table);

table->setItem(1,0, new QTableWidgetItem("30"));

itemInTable = table->item(1,0);

output << &itemInTable << endl;

window.resize(300,300);
window.show();

return a.exec&#40;&#41;;

}
@

when I execute that code I get the reference of the cell not what is inside the cell. Please keep your answers as simple as possible. Thank You

john_god

Hi mahmoud Welcome a board

You should start a new question, if it's unrelated with the previous one
There's a edit button somewhere, I think near the title

@output << itemInTable->text() << endl;@

mahmoud899

Hello, sorry for the mess, when I have a new question I'll start a new thread. The solution for the QTableWidgetItem worked. Thank You