Connecting two windows

[JonB]

@jsulm
This is partly due to my bad... :(

No declaration of StageOne was shown. I quickly read:

StageOne::StageOne(QWidget *parent) :
    QMainWindow(parent)

I read it too quickly, and thought StageOne was derived from QMainWindow. Comes from doing Python all the time instead of C++. So I misled OP by saying put in this where he should have mainWindow, my fault not his!

[russjohn834]

I'm a bit lost!

I now get a different error

mainwindow.h:25: error: C2143: syntax error: missing ';' before '*'
mainwindow.h:25: error: C4430: missing type specifier - int assumed. Note: C++ does not support default-int
mainwindow.h:25: error: C2238: unexpected token(s) preceding ';'

this is my mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QDebug>
#include <QFile>
#include <QDirIterator>
#include <QXmlStreamReader>
#include <QMessageBox>
#include "stagetwonew.h"
#include "stageone.h"

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    StageTwoNew *stagetwonew;
    StageOne *stageone;  ------------------>error points here

signals:

    void patientIdChanged(QString);


private slots:

    void on_pushButton_New_clicked();

    void on_pushButton_Open_clicked();

    void parseDataEntry(const QString dataPath);

private:
    Ui::MainWindow *ui;

};
#endif // MAINWINDOW_H

I tried complete rebuild, no luck

Any ideas where I'm wrong?

[JonB]

@russjohn834

#include "stagetwonew.h"
#include "stageone.h"
...
    StageTwoNew *stagetwonew;
    StageOne *stageone;  ------------------>error points here

Prove to us/yourself that those two header files declare StageTwoNew & StageOne as classes? (Having said that, I'd more have expected "undeclared", but at least check what I've said, even if I did mis-lead you earlier :) )

[jsulm]

@JonB said in Connecting two windows:

I read it too quickly, and thought StageOne was derived from QMainWindow

It apparently is derived from QMainWindow, but this does not have anything to do with your MainWindow.
Does StageOne include mainwindow.h? If so you have circular dependency.

[russjohn834]

@jsulm , @JonB

@jsulm said in Connecting two windows:

Does StageOne include mainwindow.h? If so you have circular dependency.

Yes. StageOne inlcude mainwindow.h. Any suggestion, How do I go about with circular dependency in this scenario?

Or is there a better way to do this (connect between two forms (QMainWindow))?

[Pablo J. Rogina]

@russjohn834 could you please state your requirement again?
How are the window(s) suppose to work together?
What data you want from what window updating what widget in what other window?

[russjohn834]

@Pablo-J-Rogina Hi,

There are two forms.
MainWindow and StageOne (Both inherits QMainWindow).

MainWindow has a signal patientIdChanged(QString), which is emitted upon clicking a button, I did this:

void MainWindow::on_pushButton_Open_clicked()
{

    QModelIndexList selection=ui->tableWidget->selectionModel()->selectedRows(0);

    this->hide();
    stageone = new StageOne(this);
    stageone->show();
    
  emit patientIdChanged(selection[0].data().toString());
    
    
}

And in StageOne I have a QLabel, its setText should get signal (Qstring) value from MainwWndow and show. That's the requirement.

I tried to do this in StageOne:

 MainWindow *mainWindow= new MainWindow(this);
connect(mainWindow, &MainWindow::patientIdChanged, ui->label, &QLabel::setText);

But this is not working

[Pablo J. Rogina]

@russjohn834 said in Connecting two windows:

Ok, it looks like you're overcomplicating things here.

So you want a string (some selection in MainWindow widget) passed to StageOne window, right?
What about having the StageOne constructor receiving such string? Pseudo-code:

void MainWindow::on_pushButton_Open_clicked()
{
     QModelIndexList selection=ui->tableWidget->selectionModel()->selectedRows(0);
 
     this->hide();
     stageone = new StageOne(selection[0].data().toString(), this);
     stageone->show();
...

and obviusly StageOne class need a change in constructor:

StageOne::StageOne(Qstring someString, QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::StageOne)
{
...

I don't see the need to deal with signals here

[russjohn834]

@Pablo-J-Rogina Thanks a lot that's exactly I was trying for.

[russjohn834]

Thank you @JonB, @jsulm , @J-Hilk and @Pablo-J-Rogina for your feedback

[jhx76]

Hi everybody.

Let's have a look to the code @russjohn834 gave us :

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    StageTwoNew *stagetwonew;
    StageOne *stageone; 

signals:

    void patientID(QString);  ----------------> signal declaration


public slots:
    void on_pushButton_New_clicked();

    void on_pushButton_Open_clicked();

    void parseDataEntry(const QString dataPath);

private:
    Ui::MainWindow *ui;

};
#endif // MAINWINDOW_H

Here we can see that the MainWindow owns an object of the class StageOne.
So we can assume that the StageOne instance is built with specifying the parent as the MainWindow, certainly with code that looks like this :

MainWindow::MainWindow() : QMainWindow() 
    : stageone(new StageOne(this))
{
}

If i am right, the parent of the stageone object is the MainWindow from which the signal patientID is emitted.

You can then write things like this :

StageOne::StageOne(QWidget *parent) :
    QMainWindow(parent), // HERE the pointed parent is the MainWindow object
    ui(new Ui::StageOne)
{
    ui->setupUi(this);
    
    // We connect the MainWindow::patientID signal emitted from the parent object
    // to the QLabel::setText slot
    connect(parent, &MainWindow::patientID, ui->label, &QLabel::setText);  
}

[Pablo J. Rogina]

@jhx76 said in Connecting two windows:

If i am right, the parent of the stageone object is the MainWindow from which the signal patientID is emitted.

it looks like there's no need to have signals at all.

[jhx76]

That's right :)

was just answering to the original question :

@russjohn834

What I'm doing wrong here?

have a nice day

[jsulm]

@russjohn834 Just a tip: to avoid circular dependencies use forward declarations:

// a.h
class B; // This is forward declaration for class B, no need to include b.h here
class A
{
    private:
        B *b;
};

// b.h
#include "a.h"
...

Forward declarations work only for pointers - in the above example it would not work if b would not be a pointer.

[russjohn834]

@jsulm Thank you for your suggestion.
Just to further clarify myself the use of forward declaration:

Two form classes MainWindow and StageOne

StageOne needs to connect with a signal from MainWindow

I did this in StageOne

class MainWindow;  // ---------> forward declaration for Mainwindow

namespace Ui {
class StageOne;
}

class StageOne : public QMainWindow
{
    Q_OBJECT

public:
    explicit StageOne(QString, QWidget *parent = nullptr);
    ~StageOne();


private:
    Ui::StageOne *ui;

    MainWindow *window;

};

I'm trying to connect as follows in StageOne:

connect(window,&MainWindow::patientIdChanged, ui->label, &QLabel::setText);

But this gives an error says:

stageone.cpp:12:21: error: incomplete type 'MainWindow' named in nested name specifier
stageone.h:10:7: note: forward declaration of 'MainWindow'

in mainwindow, i did include #include "stageone.h"

what mistake I'm doing here?

Thank you

[jsulm]

@russjohn834 You need to include mainwindow.h header in stageone.cpp

[russjohn834]

@jsulm if I include mainwindow.h header in stageone.cpp, I get follwoing error:

mainwindow.h:25: error: C2143: syntax error: missing ';' before '*'
mainwindow.h:25: error: C4430: missing type specifier - int assumed. Note: C++ does not support default-int
mainwindow.h:25: error: C2238: unexpected token(s) preceding ';'

Which points here:

#include <QMainWindow>
#include "stagetwonew.h"
#include "stageone.h"

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    StageTwoNew *stagetwonew;
    StageOne *stageone;  //--------------------> points here

signals:

    void patientIdChanged(QString);


private slots:

    void on_pushButton_New_clicked();

    void on_pushButton_Open_clicked();

    void parseDataEntry(const QString dataPath);

private:
    Ui::MainWindow *ui;

};
#endif // MAINWINDOW_H

[jsulm]

@russjohn834 Are you sure you don't include mainwindow.h in stageone.h?
Please show both header files.

[russjohn834]

@jsulm

I tried with without and with mainwindow.h in stageone.h. I'm a bit confused, you mentioned this earlier:
@jsulm said in Connecting two windows:

@russjohn834 You need to include mainwindow.h header in stageone.cpp

[russjohn834]

here are two header files:

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QDebug>
#include <QFile>
#include <QDirIterator>
#include <QXmlStreamReader>
#include <QMessageBox>
#include "stagetwonew.h"
#include "stageone.h"

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    StageTwoNew *stagetwonew;
    StageOne *stageone;

signals:

    void patientIdChanged(QString);


private slots:

    void on_pushButton_New_clicked();

    void on_pushButton_Open_clicked();

    void parseDataEntry(const QString dataPath);

private:
    Ui::MainWindow *ui;

};
#endif // MAINWINDOW_H

and stageone.h:

#ifndef STAGEONE_H
#define STAGEONE_H

#include <QMainWindow>
//#include "mainwindow.h"
#include "stagetwonew.h"



class MainWindow;
namespace Ui {
class StageOne;
}

class StageOne : public QMainWindow
{
    Q_OBJECT

public:
    explicit StageOne(QString, QWidget *parent = nullptr);
    ~StageOne();


private:
    Ui::StageOne *ui;
    MainWindow *window;
};

#endif // STAGEONE_H

I do this at stageone:

StageOne::StageOne(QString someLabel, QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::StageOne)
{
    ui->setupUi(this);

//    MainWindow *mainWindow= new MainWindow(this);
    connect(window,&MainWindow::patientIdChanged, ui->label, &QLabel::setText);  //

}

this gives an error says:

stageone.cpp:12:21: error: incomplete type 'MainWindow' named in nested name specifier
stageone.h:10:7: note: forward declaration of 'MainWindow'