error from qt unresolved C2019

Question

I write in header file private slots and the compiler gives an error:

d:\qtproject\new123\mainwindow.h:31: error: C2059: syntax error : 'public'

Please help me. I changed to public but no difference.When I clear 'public/private slots' no error comes , but writes loading D:\Qtproject\new123\debug\new123.exe... QObject::connect: No such slot QPushButton::changed() in main.cpp:18 QObject::connect: No such slot QPushButton::moved() in main.cpp:27

mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QPushButton>
namespace Ui {
  class MainWindow;
}
class MainWindow : public QMainWindow
{
  Q_OBJECT
  public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
  private slots:
    void changed();
    void moved();
    signals:
    void clicked();
  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;
}

void moved()
{
    QPushButton a;
     a.move(100,100);
}
void changed()

{   QPushButton g;
    g.setStyleSheet("QPushButton { background-color : white; color :blue; }");
}

main.cpp
#include "mainwindow.h"
#include <QApplication>
#include <QLabel>
#include <QPushButton>



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

    QApplication a(argc, argv);

    MainWindow w;

    QPushButton s("Change Color", &w);
    s.setStyleSheet("QPushButton { background-color : white; color :pink; }"
                    "QPushButton:pressed { color: blue; }");
    QObject::connect(&s, SIGNAL(clicked()), &s, SLOT(changed()));
    QPushButton d("Quit", &w);
    d.setStyleSheet("QPushButton { background-color : white; color :black; }");
    QObject::connect(&d, SIGNAL(clicked()), qApp, SLOT(quit()));
    d.move(100,0);
    QPushButton f("Move Button", &w);
    f.move(200,0);
    f.setStyleSheet("QPushButton { background-color : white; color :green; }");

    QObject::connect(&f, SIGNAL(clicked()), &f, SLOT(moved()));

    w.show();

    return a.exec();

}

Answer 1

You need to learn C++ before you learn Qt.

You declare moved() and changed() as methods of MainWindow, but then define them as free functions in the source file. You then attempt to connect the QPushButton::clicked() to these slots, but tell the connect(..) method that the slots belong to the QPushButton instead of MainWindow.

In your moved() and changed() functions you create a QPushButton in each, but don't give them a parent or add them to a layout (so they won't be visible). You also create them on the stack, so they are destroyed as the functions end.