Qt Pushbutton can not connect slot - c++

Question

I used the QT Designer to create a simple dialog and put a pushbutton on it. Then I added a custom slot on pressed() signal called test_button(). I see the generated code and can see that there is a setupUI function that has the following in it:
QObject::connect(pushButton, SIGNAL(clicked()), TestUIClass, SLOT(test_button()));
I have a testui.cpp and a testui.h:
#include <QtWidgets/QMainWindow>
#include "ui_testui.h"
class TestUI : public QMainWindow
{
Q_OBJECT
public:
TestUI(QWidget *parent = 0);
~TestUI();
virtual void test_button();
private:
Ui::TestUIClass ui;
};
This is the testui.cpp
#include "testui.h"
#include <QMessageBox>
TestUI::TestUI(QWidget *parent)
: QMainWindow(parent)
{
ui.setupUi(this);
}
TestUI::~TestUI()
{
}
void TestUI::test_button()
{
QMessageBox msgBox;
msgBox.setText("The document has been modified.");
msgBox.setInformativeText("Do you want to save your changes?");
msgBox.setStandardButtons(QMessageBox::Save | QMessageBox::Discard | QMessageBox::Cancel);
msgBox.setDefaultButton(QMessageBox::Save);
int ret = msgBox.exec();
}
My understanding is this is all I have to do, but I cant get the message box to come up.
/********************************************************************************
** Form generated from reading UI file 'testui.ui'
**
** Created by: Qt User Interface Compiler version 5.9.0
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/
#ifndef UI_TESTUI_H
#define UI_TESTUI_H
#include <QtCore/QVariant>
#include <QtWidgets/QAction>
#include <QtWidgets/QApplication>
#include <QtWidgets/QButtonGroup>
#include <QtWidgets/QHeaderView>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QPushButton>
#include <QtWidgets/QStatusBar>
#include <QtWidgets/QToolBar>
#include <QtWidgets/QWidget>
QT_BEGIN_NAMESPACE
class Ui_TestUIClass
{
public:
QWidget *centralWidget;
QPushButton *pushButton;
QMenuBar *menuBar;
QToolBar *mainToolBar;
QStatusBar *statusBar;
void setupUi(QMainWindow *TestUIClass)
{
if (TestUIClass->objectName().isEmpty())
TestUIClass->setObjectName(QStringLiteral("TestUIClass"));
TestUIClass->resize(600, 400);
centralWidget = new QWidget(TestUIClass);
centralWidget->setObjectName(QStringLiteral("centralWidget"));
pushButton = new QPushButton(centralWidget);
pushButton->setObjectName(QStringLiteral("pushButton"));
pushButton->setGeometry(QRect(120, 70, 187, 57));
TestUIClass->setCentralWidget(centralWidget);
menuBar = new QMenuBar(TestUIClass);
menuBar->setObjectName(QStringLiteral("menuBar"));
menuBar->setGeometry(QRect(0, 0, 600, 47));
TestClass->setMenuBar(menuBar);
mainToolBar = new QToolBar(TestUIClass);
mainToolBar->setObjectName(QStringLiteral("mainToolBar"));
TestUIClass->addToolBar(Qt::TopToolBarArea, mainToolBar);
statusBar = new QStatusBar(EyeGazeUIClass);
statusBar->setObjectName(QStringLiteral("statusBar"));
TestUIClass->setStatusBar(statusBar);
retranslateUi(TestUIClass);
QObject::connect(pushButton, SIGNAL(clicked()), TestUIClass, SLOT(test_button()));
QMetaObject::connectSlotsByName(TestUIClass);
} // setupUi
void retranslateUi(QMainWindow *TestUIClass)
{
TestUIClass->setWindowTitle(QApplication::translate("TestUIClass", "TestUI", Q_NULLPTR));
pushButton->setText(QApplication::translate("TestUIClass", "PushButton", Q_NULLPTR));
} // retranslateUi
};
namespace Ui {
class TestUIClass: public Ui_TestUIClass {};
} // namespace Ui
QT_END_NAMESPACE
#endif // UI_TestUI_H

Answer 1

First, you need to tell Qt that your slots actually are slots:
public slots: // or protected/private
void test_button();
There is no need for having the slot virtual...
Second, slots for 'clicked' signal are expected to accept a boolean parameter:
void test_button(bool);
For a normal push button, you can ignore the value, though.
Finally, but that's just a hint: Qt introduced with version 5 a new syntax for connecting signals/slots:
QObject::connect(pushButton, &QPushButton::clicked, theUI, &TestUIClass::test_button);
I prefer it, but it is up to you which one you use...