How to initialize a QProcess in the following windows

[Max Fleischer]

Hello,
I'm developing a UI that's controlling an external Program. In the Configuration Window, the process gets initialized and started, and I can write to it.

Configuration Window Header:

#ifndef CONFIGURATION_WINDOW_H
#define CONFIGURATION_WINDOW_H
 
#include <QWidget>
#include <QProcess>
 
class control_window;
class QProcess;
 
namespace Ui {
class configuration_window;
}
 
class configuration_window : public QWidget
{
    Q_OBJECT
 
    friend class control_window;
 
public:
    explicit configuration_window(QWidget *parent = 0);
    ~configuration_window();
 
private slots:
 
    void on_configuration_window_Exit_clicked();
 
    void on_configuration_window_Start_clicked();
 
private:
    Ui::configuration_window *ui;
 
    control_window *m_controlWindow;
 
    QProcess *m_opc_ua_server;
};
 
#endif // CONFIGURATION_WINDOW_H

#ifndef CONFIGURATION_WINDOW_H
#define CONFIGURATION_WINDOW_H

#include <QWidget>
#include <QProcess>

class control_window;
class QProcess;

namespace Ui {
class configuration_window;
}

class configuration_window : public QWidget
{
    Q_OBJECT

    friend class control_window;

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

private slots:

    void on_configuration_window_Exit_clicked();

    void on_configuration_window_Start_clicked();

private:
    Ui::configuration_window *ui;

    control_window *m_controlWindow;

    QProcess *m_opc_ua_server;
};

#endif // CONFIGURATION_WINDOW_H

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Configuration Window Source:

#include "configuration_window.h"
#include "ui_configuration_window.h"
#include "control_window.h"
#include <QMessageBox>
#include <QProcess>
#include <QDebug>
 
configuration_window::configuration_window(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::configuration_window)
{
    ui->setupUi(this);
 
    m_opc_ua_server = new QProcess(this);
 
    m_controlWindow = new control_window();
}
 
configuration_window::~configuration_window()
{
    delete ui;
}
 
void configuration_window::on_configuration_window_Exit_clicked()
{
    QApplication::quit();
}
 
void configuration_window::on_configuration_window_Start_clicked()
{
    m_opc_ua_server->setProgram("test14/testprojekt.exe");
 
    m_opc_ua_server->start(QIODevice::ReadWrite);
 
    this->close();
    m_controlWindow->show();
}

#include "configuration_window.h"
#include "ui_configuration_window.h"
#include "control_window.h"
#include <QMessageBox>
#include <QProcess>
#include <QDebug>

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

    m_opc_ua_server = new QProcess(this);

    m_controlWindow = new control_window();
}

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

void configuration_window::on_configuration_window_Exit_clicked()
{
    QApplication::quit();
}

void configuration_window::on_configuration_window_Start_clicked()
{
    m_opc_ua_server->setProgram("test14/testprojekt.exe");

    m_opc_ua_server->start(QIODevice::ReadWrite);

    this->close();
    m_controlWindow->show();
}

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In order to be able to write to it in the following windows, I have to initialize the Process. How can I do that?
If there are easier solutions to write to the Process, please tell me.

[Santosh Reddy]

If you want to write to QProcess from control_window, then better create and start the QProcess in the control_window, also create control_window in on_configuration_window_Start_clicked()

[Max Fleischer]

Ok, but I have to write to the Process in control_window and configuration_window.

[Santosh Reddy]

Then you could share the same instance of QProceess between them, or let one of the window own the QProcess and then and expose a function to write to the QProcess.

BTW, what was your original problem, writing to QProcess, use QProcess.write() (assuming the process talks on stdin)

[Max Fleischer]

I would rather share the same instance of QProcess between the windows, how can I do that?

At first I tried to write to the process from control_window, but the UI crashed because the process wasn't initialized.

control window header:

#ifndef CONTROL_WINDOW_H
#define CONTROL_WINDOW_H
 
#include <QMainWindow>
#include <QProcess>
 
namespace Ui {
class control_window;
}
 
class control_window : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit control_window(QWidget *parent = 0);
    ~control_window();
 
private slots:
    void on_control_window_Back_clicked();
 
private:
    Ui::control_window *ui;
 
    QProcess *m_opc_ua_server;
};
 
#endif // CONTROL_WINDOW_H

#ifndef CONTROL_WINDOW_H
#define CONTROL_WINDOW_H

#include <QMainWindow>
#include <QProcess>

namespace Ui {
class control_window;
}

class control_window : public QMainWindow
{
    Q_OBJECT

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

private slots:
    void on_control_window_Back_clicked();

private:
    Ui::control_window *ui;

    QProcess *m_opc_ua_server;
};

#endif // CONTROL_WINDOW_H

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control window source:

#include "control_window.h"
#include "configuration_window.h"
#include "ui_control_window.h"
 
control_window::control_window(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::control_window)
{
    ui->setupUi(this);
}
 
control_window::~control_window()
{
    delete ui;
}
 
void control_window::on_control_window_Back_clicked()
{
    m_opc_ua_server->write("j\n");
}

#include "control_window.h"
#include "configuration_window.h"
#include "ui_control_window.h"

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

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

void control_window::on_control_window_Back_clicked()
{
    m_opc_ua_server->write("j\n");
}

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Besides how can I check the Process State? It enters this if regardless whether the process is running or not.

if (m_opc_ua_server->Running)
    {
 
    }

if (m_opc_ua_server->Running)
    {

    }

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[jefftee]

Try m_opc_ua_server->state() == QProcess::Running instead.

[Max Fleischer]

Thanks, that's working.

[jefftee]

Great, also, to "share" the QProcess with other classes, either pass the QProcess pointer to the other class' constructor or create a getter method in the class that creates/owns the QProcess, for example:

QProcess* control_window::get_process()
{
    return m_opc_ua_server;
}

QProcess* control_window::get_process()
{
    return m_opc_ua_server;
}

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[Max Fleischer]

How can I pass the QProcess Pointer to the constructor?
I tried to use a getter function but the UI still crashes when I write to the process from control_window. I've put the getter function in the header of configuration_window.

configuartion window header:

#ifndef CONFIGURATION_WINDOW_H
#define CONFIGURATION_WINDOW_H
 
#include <QMainWindow>
#include <QProcess>
 
class version_selection;
class control_window;
 
namespace Ui {
class configuration_window;
}
 
class configuration_window : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit configuration_window(QWidget *parent = 0);
    ~configuration_window();
 
    void send_input_to_server();
 
    QProcess *get_process()
    {
        return m_opc_ua_server;
    }
    void set_process(QProcess *server)
    {
        m_opc_ua_server = server;
    }
 
private slots:
    void on_configuration_window_Exit_clicked();
 
    void on_configuration_window_Back_clicked();
 
    void on_configuration_window_Start_clicked();
 
private:
    Ui::configuration_window *ui;
 
    version_selection *m_version_selection;
 
    control_window *m_control_window;
 
    QProcess *m_opc_ua_server;
};
 
#endif // CONFIGURATION_WINDOW_H

#ifndef CONFIGURATION_WINDOW_H
#define CONFIGURATION_WINDOW_H

#include <QMainWindow>
#include <QProcess>

class version_selection;
class control_window;

namespace Ui {
class configuration_window;
}

class configuration_window : public QMainWindow
{
    Q_OBJECT

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

    void send_input_to_server();

    QProcess *get_process()
    {
        return m_opc_ua_server;
    }
    void set_process(QProcess *server)
    {
        m_opc_ua_server = server;
    }

private slots:
    void on_configuration_window_Exit_clicked();

    void on_configuration_window_Back_clicked();

    void on_configuration_window_Start_clicked();

private:
    Ui::configuration_window *ui;

    version_selection *m_version_selection;

    control_window *m_control_window;

    QProcess *m_opc_ua_server;
};

#endif // CONFIGURATION_WINDOW_H

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[jefftee]

In order to be able to write to it in the following windows, I have to initialize the Process. How can I do that?
If there are easier solutions to write to the Process, please tell me.

Not sure why you think you need to initialize the QProcess in order to write to it from other windows (classes), you just need to make a pointer to the QProcess instance you have already created/initialized, correct?

[Max Fleischer]

Yes that's what i meant.

[Max Fleischer]

I've figured out a solution now. I use getter and setter functions. I put the functions in public of both control_window and configuration_window and define it in the Source files.

Header configuration_window:

public:
    QProcess *process() const;
    void setProcess(QProcess *process);

public:
    QProcess *process() const;
    void setProcess(QProcess *process);

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Header control_window:

public:
    QProcess *process() const;
    void setProcess(QProcess *process);

public:
    QProcess *process() const;
    void setProcess(QProcess *process);

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Source configuration_window:

QProcess *configuration_window::process() const
{
    return m_opc_ua_server;
}
void configuration_window::setProcess(QProcess *process)
{
    m_opc_ua_server = process;
}

QProcess *configuration_window::process() const
{
    return m_opc_ua_server;
}
void configuration_window::setProcess(QProcess *process)
{
    m_opc_ua_server = process;
}

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Source control_window:

QProcess *control_window::process() const
{
    return m_opc_ua_server;
}
void control_window::setProcess(QProcess *process)
{
    m_opc_ua_server = process;
}

QProcess *control_window::process() const
{
    return m_opc_ua_server;
}
void control_window::setProcess(QProcess *process)
{
    m_opc_ua_server = process;
}

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In the Click Event that opens the next window I call the set function

m_control_window->setProcess(process());

m_control_window->setProcess(process());

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Now I can use m_opc_ua_server in control_window.