QT4 scope problem

[the_bis]

This is a very newbie question
It' a basic problem of scope between objects.
In attachment the full example code.

I have the main object (qt4testMainWindow : public QMainWindow) and I have a secondary object (qt4testData: public QObject) created by the first one.

The main object build a UI of QMainWindow type; the second handle data but have to comunicate with the main object: it must call a main object's method.

So I've created the new secondary object passing it the reference to the main UI (see "main_window.cpp" file at line 30).
It's all ok if I have to change a UI value (see "qt4test_data.cpp" at line 30) from inside the secondary object.

My problem is: how can I invoke "qt4testMainWindow::changeVar" method from the
secondary object?
I tried the method you can see in "qt4test_data.cpp" at line 32 without success:

main_ui->changeVar ( 20 );

main_ui->changeVar ( 20 );

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but I have a compiler error:

qt4test_data.cpp: In member function ‘void qt4testData::init()’:
qt4test_data.cpp:32: error: base operand of ‘->’ has non-pointer type ‘Ui::MainWindow’

qt4test_data.cpp: In member function ‘void qt4testData::init()’:
qt4test_data.cpp:32: error: base operand of ‘->’ has non-pointer type ‘Ui::MainWindow’

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Any help?
Thanks,
the_bis

[wysota]

Either use a dot (".") instead of an arrow ("->") or redesign so that you an use signals and slots without having a reference to the main window object.

[the_bis]

Either use a dot (".") instead of an arrow ("->") or redesign so that you an use signals and slots without having a reference to the main window object.

No luck

qt4test_data.cpp: In member function ‘void qt4testData::init()’:
qt4test_data.cpp:32: error: ‘class Ui::MainWindow’ has no member named ‘changeVar’

qt4test_data.cpp: In member function ‘void qt4testData::init()’:
qt4test_data.cpp:32: error: ‘class Ui::MainWindow’ has no member named ‘changeVar’

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I'm becoming crazy...
I tried first the solution you suggest... but was too difficult for me.

I post now some sample code:

"main_window.cpp":

#include "main_window.h"
#include "qt4test_data.h"
 
qt4testMainWindow::qt4testMainWindow (QWidget *parent) : QMainWindow (parent)
{
 
    ui.setupUi (this);
 
	QObject::connect(ui.horizontalSlider, SIGNAL(valueChanged(int)), ui.spinBox, SLOT(setValue(int)));
	connect (ui.pushButton2, SIGNAL(pressed()), 
		  this, SLOT(slotPush2Pressed()));
 
	init ();
 
}
 
void qt4testMainWindow::init ()
{
	QString stringToSend = "TestString";
	int integerToSend = 10;
 
	qt4testData *myqt4testData = new qt4testData ( stringToSend , integerToSend , ui );
 
	statusBar()->showMessage (tr("Starting..."));
}
 
void qt4testMainWindow::slotPush2Pressed ()
{
	qDebug ("\nqt4testMainWindow::slotPush2Pressed\n");
}
 
void qt4testMainWindow::changeVar ( int newValue )
{
	qDebug ("\nqt4testMainWindow::changeVar - newValue: %d\n" , newValue );
	ui.spinBox->setValue ( newValue );
}

#include "main_window.h"
#include "qt4test_data.h"

qt4testMainWindow::qt4testMainWindow (QWidget *parent) : QMainWindow (parent)
{
	
    ui.setupUi (this);
	
	QObject::connect(ui.horizontalSlider, SIGNAL(valueChanged(int)), ui.spinBox, SLOT(setValue(int)));
	connect (ui.pushButton2, SIGNAL(pressed()), 
		  this, SLOT(slotPush2Pressed()));

	init ();
	
}

void qt4testMainWindow::init ()
{
	QString stringToSend = "TestString";
	int integerToSend = 10;

	qt4testData *myqt4testData = new qt4testData ( stringToSend , integerToSend , ui );
	
	statusBar()->showMessage (tr("Starting..."));
}

void qt4testMainWindow::slotPush2Pressed ()
{
	qDebug ("\nqt4testMainWindow::slotPush2Pressed\n");
}

void qt4testMainWindow::changeVar ( int newValue )
{
	qDebug ("\nqt4testMainWindow::changeVar - newValue: %d\n" , newValue );
	ui.spinBox->setValue ( newValue );
}

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"main_window.h":

#include "ui_main_window.h"
 
#include <QtDebug>
 
class qt4testData;
 
class qt4testMainWindow : public QMainWindow
{
	Q_OBJECT
 
public:
	qt4testMainWindow ( QWidget *parent = 0 );
	void changeVar ( int newValue );
 
signals:
 
 
private:
	Ui::MainWindow ui;
	void init ();
 
public slots:
	void slotPush2Pressed ();
 
private slots:
 
 
};

#include "ui_main_window.h"

#include <QtDebug>

class qt4testData;

class qt4testMainWindow : public QMainWindow
{
	Q_OBJECT

public:
	qt4testMainWindow ( QWidget *parent = 0 );
	void changeVar ( int newValue );

signals:
		
		
private:
	Ui::MainWindow ui;
	void init ();
	
public slots:
	void slotPush2Pressed ();

private slots:


};

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"qt4test_data.cpp":

#include "qt4test_data.h"
 
qt4testData::qt4testData (QString& testString, int testNumber, Ui::MainWindow& main_ui_temp)
{
	qDebug ("\nqt4testData::qt4testData -> constructor");
 
	mytestString = testString;
	mytestNumber = testNumber;
 
	qDebug () << "\nqt4testData::qt4testData -> 'mytestString' variable: " << mytestString << "\n";
	qDebug () << "\nqt4testData::qt4testData -> 'mytestNumber' variable: " << mytestNumber << "\n";
 
	main_ui = main_ui_temp;
 
	init ();
}
 
void qt4testData::init ()
{
	qDebug ("\nqt4testData::init -> init");
 
	main_ui.spinBox->setValue (80);
 
	main_ui.changeVar ( 20 );
}

#include "qt4test_data.h"

qt4testData::qt4testData (QString& testString, int testNumber, Ui::MainWindow& main_ui_temp)
{
	qDebug ("\nqt4testData::qt4testData -> constructor");

	mytestString = testString;
	mytestNumber = testNumber;
		
	qDebug () << "\nqt4testData::qt4testData -> 'mytestString' variable: " << mytestString << "\n";
	qDebug () << "\nqt4testData::qt4testData -> 'mytestNumber' variable: " << mytestNumber << "\n";

	main_ui = main_ui_temp;
	
	init ();
}

void qt4testData::init ()
{
	qDebug ("\nqt4testData::init -> init");
	
	main_ui.spinBox->setValue (80);

	main_ui.changeVar ( 20 );
}

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"qt4test_data.h":

#include <QtDebug>
 
#include "ui_main_window.h"
 
class qt4testData: public QObject
{
	Q_OBJECT
 
public:
    qt4testData (QString& testString, int testNumber, Ui::MainWindow& main_ui_temp);
 
private:
	void init ();
 
	Ui::MainWindow main_ui;
	QString mytestString;
	int mytestNumber;
 
};

#include <QtDebug>

#include "ui_main_window.h"

class qt4testData: public QObject
{
	Q_OBJECT

public:
    qt4testData (QString& testString, int testNumber, Ui::MainWindow& main_ui_temp);
	
private:
	void init ();

	Ui::MainWindow main_ui;
	QString mytestString;
	int mytestNumber;

};

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Or can you tell me where to find documentation or an example to study?
Thanks,
the_bis

[wysota]

What is the type of main_ui? Where is it declared? You shouldn't do anything like:

main_ui = main_ui_temp;

main_ui = main_ui_temp;

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If you're passing a reference, then you have to treat it like one. The line above creates an unnecessary copy of the ui. Since ui is not a widget this is not forbidden, but still not advised.

You're suffering from simple C++ errors which have nothing to do with Qt. I suggest you use signals and slots to interconnect the main form and that other object.

[the_bis]

[...] I suggest you use signals and slots to interconnect the main form and that other object.

Ok, thank you far your suggestion.
I think this is the correct solution...
It works

Can you see if it is all ok?
Thanks,
the_bis

"main_window.h":

#include "ui_main_window.h"
#include "qt4test_data.h"
 
#include <QtDebug>
 
class qt4testData;
 
class qt4testMainWindow : public QMainWindow
{
	Q_OBJECT
 
public:
	qt4testMainWindow ( QWidget *parent = 0 );
	void changeVar ( int newValue );
 
signals:
 
 
private:
	void init ();
 
	Ui::MainWindow ui;
	qt4testData * myqt4testData;
 
public slots:
	void slotPush2Pressed ();
	void mainSlot ( int newValue );
 
private slots:
 
 
};

#include "ui_main_window.h"
#include "qt4test_data.h"

#include <QtDebug>

class qt4testData;

class qt4testMainWindow : public QMainWindow
{
	Q_OBJECT

public:
	qt4testMainWindow ( QWidget *parent = 0 );
	void changeVar ( int newValue );

signals:
		
		
private:
	void init ();

	Ui::MainWindow ui;
	qt4testData * myqt4testData;
	
public slots:
	void slotPush2Pressed ();
	void mainSlot ( int newValue );

private slots:


};

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"main_window.cpp":

#include "qt4test_data.h"
 
qt4testData::qt4testData ( QString& testString, int testNumber, QObject * parent )
{
 
	mytestString = testString;
	mytestNumber = testNumber;
 
	qDebug () << "\nqt4testData::qt4testData -> 'mytestString' variable: " << mytestString << "\n";
	qDebug () << "\nqt4testData::qt4testData -> 'mytestNumber' variable: " << mytestNumber << "\n";
 
	connect ( this, SIGNAL ( secondarySignal ( int ) ), parent, SLOT ( mainSlot ( int ) ) );
 
	init ();
 
}
 
void qt4testData::init ()
{
 
	qDebug ("\nqt4testData::init\n");
 
	emit ( secondarySignal ( 75 ) );
 
}
 
 
void qt4testData::secondarySlot ()
{
 
	qDebug ("\nqt4testData::secondarySlot\n");
 
}

#include "qt4test_data.h"

qt4testData::qt4testData ( QString& testString, int testNumber, QObject * parent )
{

	mytestString = testString;
	mytestNumber = testNumber;
		
	qDebug () << "\nqt4testData::qt4testData -> 'mytestString' variable: " << mytestString << "\n";
	qDebug () << "\nqt4testData::qt4testData -> 'mytestNumber' variable: " << mytestNumber << "\n";

	connect ( this, SIGNAL ( secondarySignal ( int ) ), parent, SLOT ( mainSlot ( int ) ) );

	init ();

}

void qt4testData::init ()
{
	
	qDebug ("\nqt4testData::init\n");

	emit ( secondarySignal ( 75 ) );
	
}


void qt4testData::secondarySlot ()
{
	
	qDebug ("\nqt4testData::secondarySlot\n");

}

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"qt4test_data.h":

#include <QtDebug>
 
class qt4testData: public QObject
{
	Q_OBJECT
 
public:
    qt4testData ( QString& testString, int testNumber, QObject * parent );
 
private:
	void init ();
 
	QString mytestString;
	int mytestNumber;
 
signals:
	void secondarySignal ( int newValue );
 
public slots:
	void secondarySlot ();
 
 
};

#include <QtDebug>

class qt4testData: public QObject
{
	Q_OBJECT

public:
    qt4testData ( QString& testString, int testNumber, QObject * parent );
	
private:
	void init ();

	QString mytestString;
	int mytestNumber;

signals:
	void secondarySignal ( int newValue );

public slots:
	void secondarySlot ();


};

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"qt4test_data.cpp":

#include "qt4test_data.h"
 
qt4testData::qt4testData ( QString& testString, int testNumber, QObject * parent )
{
 
	mytestString = testString;
	mytestNumber = testNumber;
 
	qDebug () << "\nqt4testData::qt4testData -> 'mytestString' variable: " << mytestString << "\n";
	qDebug () << "\nqt4testData::qt4testData -> 'mytestNumber' variable: " << mytestNumber << "\n";
 
	connect ( this, SIGNAL ( secondarySignal ( int ) ), parent, SLOT ( mainSlot ( int ) ) );
 
	init ();
 
}
 
void qt4testData::init ()
{
 
	qDebug ("\nqt4testData::init\n");
 
	emit ( secondarySignal ( 75 ) );
 
}
 
 
void qt4testData::secondarySlot ()
{
 
	qDebug ("\nqt4testData::secondarySlot\n");
 
}

#include "qt4test_data.h"

qt4testData::qt4testData ( QString& testString, int testNumber, QObject * parent )
{

	mytestString = testString;
	mytestNumber = testNumber;
		
	qDebug () << "\nqt4testData::qt4testData -> 'mytestString' variable: " << mytestString << "\n";
	qDebug () << "\nqt4testData::qt4testData -> 'mytestNumber' variable: " << mytestNumber << "\n";

	connect ( this, SIGNAL ( secondarySignal ( int ) ), parent, SLOT ( mainSlot ( int ) ) );

	init ();

}

void qt4testData::init ()
{
	
	qDebug ("\nqt4testData::init\n");

	emit ( secondarySignal ( 75 ) );
	
}


void qt4testData::secondarySlot ()
{
	
	qDebug ("\nqt4testData::secondarySlot\n");

}

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[wysota]

If it works then it's ok.