How correctly to call a function from another file?

[juliano.gomes]

Hello,

I've created an project (Qt Widget Application) with Qt Creator. Qt 5.6.1

My project structure:

myproject.pro
Headers

• dialogform.h
• mainwindow.h

Sources

• dialogform.cpp
• main.cpp
• mainwindow.cpp

Forms

• dialogform.ui
• mainwindow.ui

When I click on DialogForm pushbutton, I need to call the clear() function from MainWindow
In my code below, my project is running, but, the clear() function does not clear the lineedit.
Do anyone known how can i fix this?

Thank you very much!

dialogform.h

#ifndef DIALOGFORM_H
#define DIALOGFORM_H
 
#include <QDialog>
 
namespace Ui {
class DialogForm;
}
 
class DialogForm : public QDialog
{
    Q_OBJECT
 
public:
    explicit DialogForm(QWidget *parent = 0);
    ~DialogForm();
 
private slots:
    void on_pbClearLineEdit_clicked();
 
private:
    Ui::DialogForm *ui;
};
 
#endif // DIALOGFORM_H

#ifndef DIALOGFORM_H
#define DIALOGFORM_H

#include <QDialog>

namespace Ui {
class DialogForm;
}

class DialogForm : public QDialog
{
    Q_OBJECT

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

private slots:
    void on_pbClearLineEdit_clicked();

private:
    Ui::DialogForm *ui;
};

#endif // DIALOGFORM_H

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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();
    void clear();
 
private slots:
    void on_pbCallDialog_clicked();
 
private:
    Ui::MainWindow *ui;
};
 
#endif // 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();
    void clear();

private slots:
    void on_pbCallDialog_clicked();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

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mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "dialogform.h"
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MainWindow::on_pbCallDialog_clicked()
{
    DialogForm *dialogForm = new DialogForm(this);
    dialogForm->show();
 
    // OR
    // DialogForm d;
    // d.exec();
 
}
 
void MainWindow::clear()
{
    ui->lineEdit->clear();
}

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "dialogform.h"

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

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

void MainWindow::on_pbCallDialog_clicked()
{
    DialogForm *dialogForm = new DialogForm(this);
    dialogForm->show();

    // OR
    // DialogForm d;
    // d.exec();

}

void MainWindow::clear()
{
    ui->lineEdit->clear();
}

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dialogform.cpp

#include "dialogform.h"
#include "ui_dialogform.h"
#include "mainwindow.h"
 
DialogForm::DialogForm(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::DialogForm)
{
    ui->setupUi(this);
}
 
DialogForm::~DialogForm()
{
    delete ui;
}
 
void DialogForm::on_pbClearLineEdit_clicked()
{
    MainWindow m;
    m.clear(); // Here, is not clearing the MainWindow's lineEdit
}

#include "dialogform.h"
#include "ui_dialogform.h"
#include "mainwindow.h"

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

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

void DialogForm::on_pbClearLineEdit_clicked()
{
    MainWindow m;
    m.clear(); // Here, is not clearing the MainWindow's lineEdit
}

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main.cpp

#include "mainwindow.h"
#include <QApplication>
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
 
    return a.exec();
}

#include "mainwindow.h"
#include <QApplication>

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

    return a.exec();
}

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[stampede]

The problem is that you declare a local object in the function's scope:

void DialogForm::on_pbClearLineEdit_clicked()
{
    MainWindow m; // <-- this is allocated on the stack and will be deleted at the end of the scope
    m.clear(); // 
}

void DialogForm::on_pbClearLineEdit_clicked()
{
    MainWindow m; // <-- this is allocated on the stack and will be deleted at the end of the scope
    m.clear(); // 
}

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You should use a signal from the dialog class to inform the MainWindow that the "clear" button was pressed. Declare a signal in your Dialog class and connect it to `MainWindow::clear` slot.

[juliano.gomes]

You should use a signal from the dialog class to inform the MainWindow that the "clear" button was pressed. Declare a signal in your Dialog class and connect it to `MainWindow::clear` slot.

Thanks for your help.

I'm trying to connect, so I made the changes below, but i have this error message: invalid use of non-static member function

I've already read about signals and slots, but it isn't clear in my mind how can i do this connect.

can you give me some help?

dialogform.h

signals:
    void clearMainWindow();

signals:
    void clearMainWindow();

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mainwindow.h

public slots:
    void clear();

public slots:
    void clear();

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dialogform.cpp

void DialogForm::on_pbClearLineEdit_clicked()
{
    connect(sender, SIGNAL(clearMainWindow()),qApp ,SLOT(MainWindow::clear())); // Error: invalid use of non-static member function
}

void DialogForm::on_pbClearLineEdit_clicked()
{
    connect(sender, SIGNAL(clearMainWindow()),qApp ,SLOT(MainWindow::clear())); // Error: invalid use of non-static member function
}

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[anda_skoa]

qApp is a pointer to the QApplication object, not your MainWindow object.

The SIGNAL and SLOT macros only take function name and argument types, not class- or namespace names.

Cheers,
_

[juliano.gomes]

Here is the solution:

DialogForm::DialogForm(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::DialogForm)
{
    ui->setupUi(this);
    connect(ui->pbClearLineEdit, &QPushButton::clicked, static_cast<MainWindow*>(parent), &MainWindow::clear);
}

DialogForm::DialogForm(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::DialogForm)
{
    ui->setupUi(this);
    connect(ui->pbClearLineEdit, &QPushButton::clicked, static_cast<MainWindow*>(parent), &MainWindow::clear);
}

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[anda_skoa]

For a clean solution I would recommend to either pass the main window with its full type or to do the connect in the main window.

Cheers,
_