Transfer variable from qmainwindow to qwidget

[weiweiqiao]

this is a sample for passing data from one dialog to dialog01.
In dialog: one qpushbutton, one qlienedit, in dialog01: qlineedit;

dialog.h

#ifndef DIALOG_H
#define DIALOG_H
 
#include <QDialog>
 
class Dialog01;
 
namespace Ui {
class Dialog;
}
 
class Dialog : public QDialog
{
    Q_OBJECT
 
public:
    explicit Dialog(QWidget *parent = 0);
    ~Dialog();
 
public slots:
    void sendText();
 
signals:
    void signalText(QString text);
 
private:
    Ui::Dialog *ui;
 
    Dialog01* pDialog;
};
 
#endif // DIALOG_H

#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>

class Dialog01;

namespace Ui {
class Dialog;
}

class Dialog : public QDialog
{
    Q_OBJECT

public:
    explicit Dialog(QWidget *parent = 0);
    ~Dialog();

public slots:
    void sendText();

signals:
    void signalText(QString text);

private:
    Ui::Dialog *ui;

    Dialog01* pDialog;
};

#endif // DIALOG_H

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dialog.cpp

#include "dialog.h"
#include "ui_dialog.h"
 
#include "dialog01.h"
 
Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog),
    pDialog(new Dialog01(this))
{
    ui->setupUi(this);
 
    connect(ui->pushButton, &QPushButton::clicked,
            this, &Dialog::sendText);
    connect(this, &Dialog::signalText,
            pDialog, &Dialog01::recvText);
}
 
Dialog::~Dialog()
{
    delete ui;
}
 
void Dialog::sendText()
{
    emit signalText(ui->lineEdit->text());
 
    pDialog->setVisible(true);
}

#include "dialog.h"
#include "ui_dialog.h"

#include "dialog01.h"

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog),
    pDialog(new Dialog01(this))
{
    ui->setupUi(this);

    connect(ui->pushButton, &QPushButton::clicked,
            this, &Dialog::sendText);
    connect(this, &Dialog::signalText,
            pDialog, &Dialog01::recvText);
}

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

void Dialog::sendText()
{
    emit signalText(ui->lineEdit->text());

    pDialog->setVisible(true);
}

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dialog01.h

#ifndef DIALOG01_H
#define DIALOG01_H
 
#include <QDialog>
 
namespace Ui {
class Dialog01;
}
 
class Dialog01 : public QDialog
{
    Q_OBJECT
 
public:
    explicit Dialog01(QWidget *parent = 0);
    ~Dialog01();
 
public slots:
    void recvText(QString text);
 
private:
    Ui::Dialog01 *ui;
};
 
#endif // DIALOG01_H

#ifndef DIALOG01_H
#define DIALOG01_H

#include <QDialog>

namespace Ui {
class Dialog01;
}

class Dialog01 : public QDialog
{
    Q_OBJECT

public:
    explicit Dialog01(QWidget *parent = 0);
    ~Dialog01();

public slots:
    void recvText(QString text);

private:
    Ui::Dialog01 *ui;
};

#endif // DIALOG01_H

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dialog01.cpp

#include "ui_dialog01.h"
 
#include "dialog01.h"
 
Dialog01::Dialog01(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog01)
{
    ui->setupUi(this);
}
 
Dialog01::~Dialog01()
{
    delete ui;
}
 
void Dialog01::recvText(QString text)
{
    ui->lineEdit->setText(text);
}

#include "ui_dialog01.h"

#include "dialog01.h"

Dialog01::Dialog01(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog01)
{
    ui->setupUi(this);
}

Dialog01::~Dialog01()
{
    delete ui;
}

void Dialog01::recvText(QString text)
{
    ui->lineEdit->setText(text);
}

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main.cpp

#include <QApplication>
 
#include "maindialog.h"
 
#include "dialog.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    //MainDialog w;
    //w.show();
 
    Dialog d;
    d.show();
 
    return a.exec();
}

#include <QApplication>

#include "maindialog.h"

#include "dialog.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    //MainDialog w;
    //w.show();

    Dialog d;
    d.show();

    return a.exec();
}

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[franzib]

Ah I see, I have to implement two connections. One signal in each class and one slot in each class and the variable is emitted in the slot functions, right?

[weiweiqiao]

yeah, pushbutton's click have no param, so you should send a slot with no param, however, you could emit signal with param which you want in slot method.

[anda_skoa]

Ah I see, I have to implement two connections. One signal in each class and one slot in each class and the variable is emitted in the slot functions, right?

No.
One signal at the source and one slot at the receiver is enough.

And you don't need signal/slots at all if all you want is to provide initial data to the other object.

The example is a demonstration on how to use signal/slots but in a real project just useless code complexity.

Cheers,
_