Qt passing a Value from one window to antother - c++

Question

I am quite new to programming, so hopefully someone can help me out. After calculating a value with a function and storing it into the variable with a setter, I want to call it in my viswindow.cpp to visualize it in a Graph. In the mainwindow the right value is calculated and stored by pressing a button, which also opens the viswindow. I tried to pass it with a pointer or with signals and slots, but it wouldn't work.
mainwindow.cpp:
double MainWindow::berechneFussabdruck(double strecke, int anzahl, double sfcWert)
{
if(strecke <= 1500 && strecke > 0){
double aequivalente_Co2 = (((sfcWert*3.116*50*(((0.0011235955)*(strecke-2*48.42))+0.233))*0.001)/anzahl);
setAequivalente(aequivalente_Co2);
}
else{
double aequivalente_Co2 = (((sfcWert*3.116*75*(((0.0011235955)*(strecke-2*208))+0.833))*0.001)/anzahl);
setAequivalente(aequivalente_Co2);
}
return aequivalente_Co2;
}
Button to open viswindow:
void MainWindow::on_pushButton_clicked()
{
MainWindow::berechneFussabdruck(strecke, anzahl, sfcWert);
visWindow = new VisWindow(this);
visWindow->show();
}
viswindow.cpp:
VisWindow::VisWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::VisWindow)
{
ui->setupUi(this);
...
*set0 << aequivalente_Co2 << aequivalente_Co2;
*set1 << 11.07 << 0;
*set2 << 0 << 0.49;
...
}
Thanks for helping!

Answer 1

Here are examples of:
Single time value transfer from MainWindow to VisWindow in constructor parameter.
Value update from MainWindow to VisWindow by slot-signal chain.
Value update from MainWindow to VisWindow by direct call of VisWindow->updateValue() slot as regular function.
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "viswindow.h"
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
private slots:
void on_pushButton_clicked();
void on_pushButton_2_clicked();
void on_pushButton_3_clicked();
signals:
void updatevalue(const double value);
private:
Ui::MainWindow *ui;
VisWindow * m_viswindow;
};
#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 MainWindow::on_pushButton_clicked() {
m_viswindow = new VisWindow(12.34, nullptr);
connect(this, &MainWindow::updatevalue,
m_viswindow, &VisWindow::updateValue);
m_viswindow->show();
}
void MainWindow::on_pushButton_2_clicked() {
emit updatevalue(23.45);
}
void MainWindow::on_pushButton_3_clicked() {
m_viswindow->updateValue(45.67);
}
viswindow.h
#ifndef VISWINDOW_H
#define VISWINDOW_H
#include <QWidget>
namespace Ui {
class VisWindow;
}
class VisWindow : public QWidget
{
Q_OBJECT
public:
explicit VisWindow(const double value, QWidget *parent = nullptr);
~VisWindow();
public slots:
void updateValue(const double value);
private:
Ui::VisWindow *ui;
};
#endif // VISWINDOW_H
viswindow.cpp
#include "viswindow.h"
#include "ui_viswindow.h"
VisWindow::VisWindow(const double value, QWidget *parent) :
QWidget(parent),
ui(new Ui::VisWindow)
{
ui->setupUi(this);
ui->lblValue->setText(QString::number(value,'f',2));
this->setWindowTitle("VisWindow");
}
VisWindow::~VisWindow() {
delete ui;
}
void VisWindow::updateValue(const double value) {
ui->lblValue->setText(QString::number(value,'f',2));
}