Connection QPushButton to a Function in main.cpp

[suggi87]

Hello,
I have a main.cpp with a window and also a QPushButton.

@#include <QApplication>
#include <QPushButton>
#include <QtWidgets>
#include <kfz.h>
#include <diagramm.h>

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

QApplication app(argc, argv);

QWidget *window = new QWidget;
QGridLayout *box = new QGridLayout(window);

...

QObject::connect(button, SIGNAL(clicked()),&app, SLOT(onbuttonclicked()));

...
@
I have another class Diagramm.cpp
@#include "diagramm.h"
#include "ui_diagramm.h"

Diagramm::Diagramm(QWidget *parent) :
QDialog(parent),
ui(new Ui::Diagramm)
{
ui->setupUi(this);
}

Diagramm::~Diagramm()
{
delete ui;
}

void Diagramm::onbuttonclicked()
{
Diagramm dia;
dia.setModal(true);
dia.exec();
}
@

and Diagramm.h
@#ifndef DIAGRAMM_H
#define DIAGRAMM_H

#include <QDialog>

namespace Ui {
class Diagramm;
}

class Diagramm : public QDialog
{
Q_OBJECT

public:
explicit Diagramm(QWidget *parent = 0);
~Diagramm();
public slots:
void onbuttonclicked();

private:
Ui::Diagramm *ui;
};

#endif // DIAGRAMM_H
@

If i click the button, i want to execute the onbuttonclicked() function from the Diagramm class.

The Error is:
there is no such slot QApplication:onbuttonclicked()

I tried also
QObject::connect(button, SIGNAL(clicked()),this, SLOT(onbuttonclicked()));

-> invalid use of this in non-member function

Can anyone help me? I am new at QT :(