Connecting two windows

[russjohn834]

Hi all,

I have a basic question:

I need to connect a signal (QString) from a QMainWindow (MainWindow) to slot (QLabel::settext) from QMainWindow (StageOne). I did this:

#include "stageone.h"
#include "ui_stageone.h"
#include "mainwindow.h"

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

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

}

this gives an error says:

stageone.cpp:11:14: error: 'MainWindow' does not refer to a value
mainwindow.h:17:7: note: declared here

What I'm doing wrong here?

Thank you

[JonB]

@russjohn834 said in Connecting two windows:

&MainWindow, &MainWindow::patientID

Start with:

• &MainWindow probably should be this
• &MainWindow::patientID needs to be a signal which is emitted when something happens. Yours looks to me like a member variable?

There will be further issues after these...

However, I am wondering whether you do not have/want any signal at all, and this should be nothing to do with signals/slots. If all you want to do is set the text of that label in the constructor don't you just want:

ui->label->setText("something");

Depends what you are actually trying to achieve? Is this really to do with a signal happening or not?

[russjohn834]

@JonB Thank you.

&MainWindow::patientID is a signal which is emitted as

emit patientID(selection[0].data().toString());

So I need to setText label in another window (StageOne). The text is selection[0].data().toString()

[russjohn834]

@JonB

I tried this:

connect(this, &MainWindow::patientID, ui->label, &QLabel::setText);

this throws a different error:

stageone.cpp:11:5: error: no matching member function for call to 'connect'
qobject.h:228:43: note: candidate function [with Func1 = void (MainWindow::*)(QString), Func2 = void (QLabel::*)(const QString &)] not viable: no known conversion from 'StageOne *' to 'const typename QtPrivate::FunctionPointer<void (MainWindow::*)(QString)>::Object *' (aka 'const MainWindow *') for 1st argument
qobject.h:208:36: note: candidate function not viable: no known conversion from 'void (MainWindow::*)(QString)' to 'const char *' for 2nd argument
qobject.h:211:36: note: candidate function not viable: no known conversion from 'void (MainWindow::*)(QString)' to 'const QMetaMethod' for 2nd argument
qobject.h:463:41: note: candidate function not viable: no known conversion from 'void (MainWindow::*)(QString)' to 'const char *' for 2nd argument
qobject.h:269:13: note: candidate template ignored: requirement '!QtPrivate::FunctionPointer<void (QLabel::*)(const QString &)>::IsPointerToMemberFunction' was not satisfied [with Func1 = void (MainWindow::*)(QString), Func2 = void (QLabel::*)(const QString &)]
qobject.h:308:13: note: candidate template ignored: requirement 'QtPrivate::FunctionPointer<void (QLabel::*)(const QString &)>::ArgumentCount == -1' was not satisfied [with Func1 = void (MainWindow::*)(QString), Func2 = void (QLabel::*)(const QString &)]
qobject.h:260:13: note: candidate function template not viable: requires 3 arguments, but 4 were provided
qobject.h:300:13: note: candidate function template not viable: requires 3 arguments, but 4 were provided

[JonB]

@russjohn834
I would suggest that patientID is not at all a good name for a signal or a method! Something more like patientIdChanged would be usual and intelligible.

The error message is complaining about your first parameter, &MainWindow. I don't know what you think that is. As I said, you probably mean this there.

[JonB]

@russjohn834
In answer to your new messages, when you wrote earlier

&MainWindow::patientID is a signal which is emitted as

emit patientID(selection[0].data().toString());

this is not good enough for people to help you, I would suggest. We need to see the definition in the .cpp file and the declaration in the .h file....

[jsulm]

@russjohn834 Please show the exact declaration of patientID...

[russjohn834]

@jsulm Hi,

I declared patientID as:

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 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

[jsulm]

@russjohn834 Looks good. Try a complete rebuild: delete build folder, run qmake and then build.

[russjohn834]

@jsulm

I'm getting still the same error:

stageone.cpp:11:5: error: no matching member function for call to 'connect'
qobject.h:228:43: note: candidate function [with Func1 = void (MainWindow::*)(QString), Func2 = void (QLabel::*)(const QString &)] not viable: no known conversion from 'StageOne *' to 'const typename QtPrivate::FunctionPointer<void (MainWindow::*)(QString)>::Object *' (aka 'const MainWindow *') for 1st argument
qobject.h:208:36: note: candidate function not viable: no known conversion from 'void (MainWindow::*)(QString)' to 'const char *' for 2nd argument
qobject.h:211:36: note: candidate function not viable: no known conversion from 'void (MainWindow::*)(QString)' to 'const QMetaMethod' for 2nd argument
qobject.h:463:41: note: candidate function not viable: no known conversion from 'void (MainWindow::*)(QString)' to 'const char *' for 2nd argument
qobject.h:269:13: note: candidate template ignored: requirement '!QtPrivate::FunctionPointer<void (QLabel::*)(const QString &)>::IsPointerToMemberFunction' was not satisfied [with Func1 = void (MainWindow::*)(QString), Func2 = void (QLabel::*)(const QString &)]
qobject.h:308:13: note: candidate template ignored: requirement 'QtPrivate::FunctionPointer<void (QLabel::*)(const QString &)>::ArgumentCount == -1' was not satisfied [with Func1 = void (MainWindow::*)(QString), Func2 = void (QLabel::*)(const QString &)]
qobject.h:260:13: note: candidate function template not viable: requires 3 arguments, but 4 were provided
qobject.h:300:13: note: candidate function template not viable: requires 3 arguments, but 4 were provided

This is how I call the connect:

#include "stageone.h"
#include "ui_stageone.h"
#include "mainwindow.h"

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

    connect(this, &MainWindow::patientID, ui->label, &QLabel::setText);  //

}

Any idea?

[J.Hilk]

@russjohn834

do you happen to have a function body inside mainwindow.cpp ?

somethinglike:
void MainWindow::patientID(QString string)

That's not allowed for signals

[J.Hilk]

@russjohn834 said in Connecting two windows:

connect(this, &MainWindow::patientID, ui->label, &QLabel::setText);

Oh its much simpler

You class is not called MainWindow, but StageOne

connect(this, &StageOne::patientID, ui->label, &QLabel::setText); 

[jsulm]

@J-Hilk @russjohn834 I'm lost. The signal is declared in MainWindow, but connect is in StageOne.
@russjohn834 What is it now?!

[russjohn834]

@jsulm @J-Hilk ,

Still the same issue.

I changed the name of signal from patientID to patientIdChanged.

signal is Declared and emitted in MainWindow. Connection is in StageOne (with a QLabel).

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

    connect(this, &MainWindow::patientIdChanged, ui->label, &QLabel::setText);  //
}

the error says:

stageone.cpp:11:5: error: no matching member function for call to 'connect'
qobject.h:228:43: note: candidate function [with Func1 = void (MainWindow::*)(QString), Func2 = void (QLabel::*)(const QString &)] not viable: no known conversion from 'StageOne *' to 'const typename QtPrivate::FunctionPointer<void (MainWindow::*)(QString)>::Object *' (aka 'const MainWindow *') for 1st argument
qobject.h:208:36: note: candidate function not viable: no known conversion from 'void (MainWindow::*)(QString)' to 'const char *' for 2nd argument
qobject.h:211:36: note: candidate function not viable: no known conversion from 'void (MainWindow::*)(QString)' to 'const QMetaMethod' for 2nd argument
qobject.h:463:41: note: candidate function not viable: no known conversion from 'void (MainWindow::*)(QString)' to 'const char *' for 2nd argument
qobject.h:269:13: note: candidate template ignored: requirement '!QtPrivate::FunctionPointer<void (QLabel::*)(const QString &)>::IsPointerToMemberFunction' was not satisfied [with Func1 = void (MainWindow::*)(QString), Func2 = void (QLabel::*)(const QString &)]
qobject.h:308:13: note: candidate template ignored: requirement 'QtPrivate::FunctionPointer<void (QLabel::*)(const QString &)>::ArgumentCount == -1' was not satisfied [with Func1 = void (MainWindow::*)(QString), Func2 = void (QLabel::*)(const QString &)]
qobject.h:260:13: note: candidate function template not viable: requires 3 arguments, but 4 were provided
qobject.h:300:13: note: candidate function template not viable: requires 3 arguments, but 4 were provided

[jsulm]

@russjohn834 Come on it is not about patientID!
In the connect bellow this is NOT MainWindow, but StageOne!
It simply can't work this way!

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

    connect(this, &MainWindow::patientIdChanged, ui->label, &QLabel::setText);  // this != MaiNWindow*!
}

If you want to connect in StageOne then you need an instance of MainWindow:

StageOne::StageOne(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::StageOne)
{
    ui->setupUi(this);
    MainWindow *mainWindow = new MainWindow(...);
    connect(mainWindow, &MainWindow::patientIdChanged, ui->label, &QLabel::setText);  // this != MaiNWindow*!
}

[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))?