How can I call the "pushButton" in main.cpp? - qt

Question

mainwindow.h:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
main.cpp
#include <QtGui/QApplication>
#include "mainwindow.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
QObject::connect(pushButton, SIGNAL(clicked()),
&a, SLOT(quit()));
return a.exec();
}
All the codes are given above. In a general Qt GUI program, I put a pushButton on the UI Form and tried to use it in main.cpp. But below error was given:
main.cpp:10: Error:'pushButton' was not declared in this scope
Could you please give me a solution? How can I call it in main.cpp?
Thanks!
Complement1:
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
QObject::connect(ui->pushButton, SIGNAL(clicked()),
QCoreApplication::instance(), SLOT(close()));
}
MainWindow::~MainWindow()
{
delete ui;
}
If I do it this way, then the program can run but cannot close the whole application. I guess that is because the QCoreApplication::instance() returns null due to in the constructor phase the QApplication doesn't exist, right?
Complement2:
mainwindow.cpp
void MainWindow::on_pushButton_clicked()
{
close();
}
One solution is to add new slot of the pushButton in mainwindow.cpp, like above.
But still I hope to know how to do it my way (main part of this post)?
Complement3:
Alberto's code works fine by using QWidget as below way.
ui->setupUi(this);
connect(ui->pushButton,SIGNAL(clicked()),this,SLOT(close()));

Answer 1

Your first approach can't work because, as compiler says, you didn't defined a QPushButton in main.cpp scope. So compiler can't find it.
Right approach is your last one. You develop a .ui file in which you add a QPushButton and then in c++ code that handles your .ui file(in your example a QMainWindow subclass) you connect it with a slot. But your connect call is wrong. This is my code:
//widget.h:
#ifndef WIDGET_H
#define WIDGET_H
#include <QWidget>
namespace Ui {
class Widget;
}
class Widget : public QWidget
{
Q_OBJECT
public:
explicit Widget(QWidget *parent = 0);
~Widget();
private:
Ui::Widget *ui;
};
#endif // WIDGET_H
//widget.cpp:
#include "widget.h"
#include "ui_widget.h"
#include <QtGui>
Widget::~Widget()
{
delete ui;
}
Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
ui->setupUi(this);
connect(ui->pushButton,SIGNAL(clicked()),this,SLOT(close()));
}
//widget.ui:
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>Widget</class>
<widget class="QWidget" name="Widget">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>93</width>
<height>41</height>
</rect>
</property>
<property name="windowTitle">
<string>Widget</string>
</property>
<layout class="QVBoxLayout" name="verticalLayout">
<item>
<widget class="QPushButton" name="pushButton">
<property name="text">
<string>PushButton</string>
</property>
</widget>
</item>
</layout>
</widget>
<layoutdefault spacing="6" margin="11"/>
<resources/>
<connections/>
</ui>
//main.cpp:
#include <QtGui/QApplication>
#include "widget.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget w;
w.show();
return a.exec();
}
with: connect(ui->pushButton,SIGNAL(clicked()),this,SLOT(close()));
which we can simplify in this way: connect(1,2,3,4);
when 2 is emitted because user does something on 1, do 4 on 3.
translated: when user click on pushButton(defined into ui file), do close on this(QMainWindow subclass). And if you take a look at your main.cpp code, MainWindow is the main widget you show to the user. So you're closing the whole app.