Wierd behaviour in a slot routine

[koenig]

Hi,

Firslty I'm very new to QT (as well as GUI programming) but quickly falling in love with it :)

Having said that however, I have hit my first wall which is probably a lack of understanding something. I am useing eclipse with QT integration (V4.6).

As a test I have crated a form using the designer with a simple text entry widget and a button

I then created a slot for the buttons clicked signal

In the routine processing the signal I read the text from the entry and set the text for the button label to reflect that.

Copiled and ran fine. I can enter text in the entry box and when I click on the button it's label changes to what I entered.

However the text in the entry box does not get cleared so I issued the clear method on it following the set text method on the button.

Now when I click on th button the text in the entry box gets cleared which is fine, but so does the label of the button which I don't get.

Below is the implementation of the slot function:


void qt_test::on_enterButton_clicked()
{
QString buttonName = ui.lineInput->displayText();
ui.enterButton->setText(buttonName);
ui.lineInput->clear();
}


ui.lineIput is of class QLineEdit
ui.enterButton is of class QPushButton

inially the push button has the text "Push" on it then when I push it it get cleared irrespective of what has been entered in the lineInput

The itneresting thing is that if I do this:


void qt_test::on_enterButton_clicked()
{
QString buttonName = ui.lineInput->displayText();
buttonName += "ABC";
ui.enterButton->setText(buttonName);
ui.lineInput->clear();
}

The push button text gets set to "ABC" again irrespective of what is entered in lineInput.

Any one able to tell me why this is so?

Thanks!

[boudie]

This works here without any problem:


void MainWindow::on_enterButton_clicked()
{
QString buttonName = ui->lineEdit->displayText();
ui->pushButton->setText(buttonName);
ui->lineEdit->clear();
}

I made the form with QtCreator 1.3.0.

[koenig]

Ok well that stumps me then :)

I guess one other bit of info is that I have been doing this on Windows 7, although can't think of any dependacy on the OS off the top of my head that would cause such a thing.

[boudie]

Ok, Let's change


QString buttonName = ui.lineInput->displayText();

into this


QString buttonName ( ui.lineInput->displayText());

[koenig]

Ok tried that, made no differance.

I also just updated to Qt 4.6.1 (changed all the paths appropriately too) that also made no differance

[koenig]

For completeness I'm posting all code from this project, maybe I've stuffed something elsewhere :)

main.cpp:


#include "qt_test.h"

#include <QtGui>
#include <QApplication>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
qt_test w;
w.show();
return a.exec();
}


ui_qt_test.h:


#ifndef UI_QT_TEST_H
#define UI_QT_TEST_H

#include <QtCore/QVariant>
#include <QtGui/QAction>
#include <QtGui/QApplication>
#include <QtGui/QButtonGroup>
#include <QtGui/QHeaderView>
#include <QtGui/QLineEdit>
#include <QtGui/QPushButton>
#include <QtGui/QTextBrowser>
#include <QtGui/QWidget>

QT_BEGIN_NAMESPACE

class Ui_qt_testClass
{
public:
QTextBrowser *textOut;
QLineEdit *lineInput;
QPushButton *enterButton;
QPushButton *quitButton;

void setupUi(QWidget *qt_testClass)
{
if (qt_testClass->objectName().isEmpty())
qt_testClass->setObjectName(QString::fromUtf8("qt_testClass"));
qt_testClass->resize(661, 407);
textOut = new QTextBrowser(qt_testClass);
textOut->setObjectName(QString::fromUtf8("textOut"));
textOut->setGeometry(QRect(80, 60, 511, 192));
lineInput = new QLineEdit(qt_testClass);
lineInput->setObjectName(QString::fromUtf8("lineInput"));
lineInput->setGeometry(QRect(80, 270, 291, 20));
enterButton = new QPushButton(qt_testClass);
enterButton->setObjectName(QString::fromUtf8("enterButton"));
enterButton->setGeometry(QRect(410, 270, 75, 23));
quitButton = new QPushButton(qt_testClass);
quitButton->setObjectName(QString::fromUtf8("quitButton"));
quitButton->setGeometry(QRect(410, 360, 75, 23));

retranslateUi(qt_testClass);
QObject::connect(quitButton, SIGNAL(clicked()), qt_testClass, SLOT(close()));

QMetaObject::connectSlotsByName(qt_testClass);
} // setupUi

void retranslateUi(QWidget *qt_testClass)
{
qt_testClass->setWindowTitle(QApplication::translate("qt_testClass", "qt_test", 0, QApplication::UnicodeUTF8));
enterButton->setText(QApplication::translate("qt_testClass", "Enter", 0, QApplication::UnicodeUTF8));
quitButton->setText(QApplication::translate("qt_testClass", "Quit", 0, QApplication::UnicodeUTF8));
} // retranslateUi

};

namespace Ui {
class qt_testClass: public Ui_qt_testClass {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_QT_TEST_H


qt_test.h:


#ifndef QT_TEST_H
#define QT_TEST_H

#include <QtGui/QWidget>
#include "ui_qt_test.h"

class qt_test : public QWidget
{
Q_OBJECT

public:
qt_test(QWidget *parent = 0);
~qt_test();

public slots:
void on_enterButton_clicked();

private:
Ui::qt_testClass ui;
};

#endif // QT_TEST_H



qt_test.cpp:


#include "qt_test.h"
#include <QString>

qt_test::qt_test(QWidget *parent)
: QWidget(parent)
{
ui.setupUi(this);
connect(ui.enterButton, SIGNAL(clicked()), this, SLOT(on_enterButton_clicked()));
}

qt_test::~qt_test()
{

}

void qt_test::on_enterButton_clicked()
{
QString buttonName (ui.lineInput->displayText());
buttonName += "ABC";
ui.enterButton->setText(buttonName);
ui.lineInput->clear();


}

[koenig]

Oh I've figured it out!!!! :)

As I'm very new to this framework I got caught by the signal/slot connection method, I didn't realise that when I named the slot function on_enterButton_clicked() the framework would implicitly connect the the clicked signal for me. So I also issued an explicit connect statement in the constructor. As a result the slot function was being executed twice, and so the second time it exectued the text bas was already cleared and so the button label also got cleared.

D'OH!!!! :)

Anyway, thanks for the help, actually just knowing that it work for someone else made me dig in different directions, I was starting to loose my mind there a bit :)

[boudie]

LOL!
:D:D:D

And nobody noticed it...