Accessing widgets from my class

Flurite

Hi,

I've been working on a timer application, but have run into trouble when converting it to a Qt Widget Application. As it is right, now, I decided to make my own Stopwatch class, and the basic framework of it is as following:

@
class Stopwatch : public QObject
{
Q_OBJECT
private:
QTimer* timer;
public:
Stopwatch()
{
connect(timer, SIGNAL(timeout()), this, SLOT(changeTime()));
}
private slots:
void changeTime();
};

void Stopwatch::changeTime()
{
/* code (parts try to access the widgets) */
}
@

A problem with this is that I cannot access widgets from the class, because I have not declared a pointer to the MainWindow, which is called "Clock_Application" in this program. I tried declaring a pointer to Clock_Application by adding it to the private members of my class:

@
private:
QTimer* timer;
Clock_Application* ui;
@

But then it complains that Output(a lineEdit in my widget) does not exist, which it obviously does, because in my previous widget application (it was laggy, so I am revise it), Output was there.

So any solutions to accessing my widgets from my class function?

MuldeR

I think your Stopwatch class shouldn't have to know about Clock_Application.

Let's assume your Stopwatch class wants to write something to a QLabel widget on a timer event, then make it as general as possible and just store a pointer to a QLabel that is set in the constructor:

@ class Stopwatch : public QObject
{
Q_OBJECT
private:
QTimer* m_timer;
QLabel* m_label;
public:
Stopwatch(QLabel* label)
{
m_timer = new QTimer(); //haven't you forgot this ???
m_label = label; //remember pointer for later use!
connect(m_timer, SIGNAL(timeout()), this, SLOT(changeTime()));
}
~Stopwatch(void)
{
delete m_timer;
}
private slots:
void changeTime();
};

void Stopwatch::changeTime()
{
    m_label->doSomething();
}

@

Flurite

[quote author="MuldeR" date="1335142286"]I think your Stopwatch class shouldn't have to know about Clock_Application.

Let's assume your Stopwatch class wants to write something to a QLabel widget on a timer event, then make it as general as possible and just store a pointer to a QLabel that is set in the constructor:

@ class Stopwatch : public QObject
{
Q_OBJECT
private:
QTimer* m_timer;
QLabel* m_label;
public:
Stopwatch(QLabel* label)
{
m_timer = new QTimer(); //haven't you forgot this ???
m_label = label; //remember pointer for later use!
connect(m_timer, SIGNAL(timeout()), this, SLOT(changeTime()));
}
~Stopwatch(void)
{
delete m_timer;
}
private slots:
void changeTime();
};

void Stopwatch::changeTime()
{
    m_label->doSomething();
}

@[/quote]

Thanks for the response.

One last question though. Where would I create a new instance of Stopwatch though? To store the GUI as a parameter, I would have to be able to access the widget. Is this right? If so, is there a work around?

MuldeR

well, usually your application will look something like:
@main()
{
QApplication app(argc, argv);
mainWindow = new MyMainWindow();
mainWindow->show();
int ret = app.exec();
delete mainWindow;
return ret;
}@

And your MyMainWindow class may look like:
@class MyMainWindow: public QMainWindow, private Ui::MyMainWindow
{
Q_OBJECT

public:
MyMainWindow(QWidget *parent = 0);
~MyMainWindow(void);
private:
m_stopwatch *Stopwatch; //member variable to store the Stopwatch pointer

....

}@

In the constructor of MyMainWindow you would set up everything:
@MyMainWindow::MyMainWindow(QWidget *parent)
{
//Init the dialog, from the .ui file
setupUi(this);

//Create the Stopwatch object and pass the pointer to our QLabel!
m_stopwatch = new Stopwatch(myLabel&#41;;

....

}@

Don't forget the clean-up:
@MyMainWindow::~MyMainWindow(void)
{
delete m_stopwatch;
}@

Note: The code above assumes that there is QLabel "myLabel" in the .ui file!

mlong

Actually, there's probably no real reason to break the QTimer functionality into its own Stopwatch class, if it's supposed to just be updating the label in your MainWindow. In that case, just create a QTimer which is a member of MainWindow and set up a private slot in MainWindow which will get called when the timer fires.

Since your label widget should be visible from within MainWindow, then you shouldn't have any problems updating it from a slot in MainWindow.

Flurite

[quote author="mlong" date="1335210337"]Actually, there's probably no real reason to break the QTimer functionality into its own Stopwatch class, if it's supposed to just be updating the label in your MainWindow. In that case, just create a QTimer which is a member of MainWindow and set up a private slot in MainWindow which will get called when the timer fires.

Since your label widget should be visible from within MainWindow, then you shouldn't have any problems updating it from a slot in MainWindow.
[/quote]

I've tried that idea before, but unfortunately it gives me this error, which I have absolutely no idea why it does give it to me:

invalid use of incomplete struct type 'struct Ui::Clock_Application'
forward declaration of 'struct Ui::Clock_Application'

[quote author="MuldeR" date="1335210138"]well, usually your application will look something like:
@main()
{
QApplication app(argc, argv);
mainWindow = new MyMainWindow();
mainWindow->show();
int ret = app.exec();
delete mainWindow;
return ret;
}@

And your MyMainWindow class may look like:
@class MyMainWindow: public QMainWindow, private Ui::MyMainWindow
{
Q_OBJECT

public:
MyMainWindow(QWidget *parent = 0);
~MyMainWindow(void);
private:
m_stopwatch *Stopwatch; //member variable to store the Stopwatch pointer

....

}@

In the constructor of MyMainWindow you would set up everything:
@MyMainWindow::MyMainWindow(QWidget *parent)
{
//Init the dialog, from the .ui file
setupUi(this);

//Create the Stopwatch object and pass the pointer to our QLabel!
m_stopwatch = new Stopwatch(myLabel&#41;;

....

}@

Don't forget the clean-up:
@MyMainWindow::~MyMainWindow(void)
{
delete m_stopwatch;
}@

Note: The code above assumes that there is QLabel "myLabel" in the .ui file![/quote]

I am running into problems everywhere. Somehow, it's complaining that I have multiple declarations in this piece of code:

@class Clock_Application : public QMainWindow
{
Q_OBJECT

public:
explicit Clock_Application(QWidget parent = 0);
~Clock_Application();
public slots:
void timer_Start();
private:
Ui::Clock_Application ui;
QTimer timer;
Stopwatch stopwatchClass;
};
///////////////////////////////////
class Stopwatch : public QObject
{
Q_OBJECT
private:
QTimer* timer;
QLineEdit* OutputToChange;
public:
Stopwatch(QLineEdit* output)
{
timer = new QTimer();
OutputToChange = output;
connect(timer, SIGNAL(timeout()), this, SLOT(changeTime(QLineEdit*)));
}
private slots:
void changeTime(QLineEdit* output);
};

void Stopwatch::changeTime(QLineEdit* output)
{
/* code that tries to access widget */
}
@

multiple definition of 'Stopwatch::changeTime(QLineEdit*)'
first defined here

This error happened twice.

MuldeR

Have you created a "Clock_Application.ui" file with QtDesigner?

Also have you compiled the .ui file with UIC to get the corresponding include (.h) file?

And have you included that .h file in the file where your Clock_Application class is declared?

mlong

You can't connect timeout() to changeTime(QLineEdit*). The slot has to have the same (or fewer)
parameters than the signal.

Remember, the connect is just setting up a connection that will be called when some signal is emitted later on. How should timer's timeout() have any idea what to pass into the QLineEdit* parameter to changeTime?

mlong

[quote author="Flurite" date="1335214034"]
I’ve tried [adding a QTimer to the MainWindow's code] before, but unfortunately it gives me this error, which I have absolutely no idea why it does give it to me:
invalid use of incomplete struct type ‘struct Ui::Clock_Application’
forward declaration of ‘struct Ui::Clock_Application’
[/quote]

You should work on using the simplest model and fixing that particular error instead of trying to contrive an alternate solution which is, honestly, cumbersome and kludgy.

If you could post code on how you tried to use the in-class QTimer method, we can help you fix the error you mentioned.

Flurite

[quote author="mlong" date="1335215064"]
[quote author="Flurite" date="1335214034"]
I’ve tried [adding a QTimer to the MainWindow's code] before, but unfortunately it gives me this error, which I have absolutely no idea why it does give it to me:
invalid use of incomplete struct type ‘struct Ui::Clock_Application’
forward declaration of ‘struct Ui::Clock_Application’
[/quote]

You should work on using the simplest model and fixing that particular error instead of trying to contrive an alternate solution which is, honestly, cumbersome and kludgy.

If you could post code on how you tried to use the in-class QTimer method, we can help you fix the error you mentioned.[/quote]

I see.

This is what I am working with:

@
class Clock_Application : public QMainWindow
{
Q_OBJECT

public:
explicit Clock_Application(QWidget *parent = 0);
~Clock_Application();
public slots:
void timer_Start();
void changeTime();
private:
Ui::Clock_Application ui;
QTimer timer;
};

void Clock_Application::timer_Start()
{
timer = new QTimer();
connect(timer, SIGNAL(timeout()), this, SLOT(changeTime()));
timer->start(1000);
}

void Clock_Application::changeTime()
{
/* do you need to see this function? */
}
@

Take note that timer_start() is connected to an on-click signal. Also, I do not have anything to do with this in my .cpp files as I believe that these functions are controlled by the signals.

MuldeR

This code excerpt looks okay to me.

Except that you should not create a new QTimer object every time timer_Start() is called. The function may be called several times. Better create the timer object once in the constructor of Clock_Application and destroy it in the destructor of Clock_Application. If you insist to create the QTimer object in timer_Start(), at least set the member variable 'timer' to NULL in the constructor and, if 'timer' is unequal NULL (i.e. an object has been created in a previous call to timer_Start()), destroy the "old" object before you create the new one. Even with the latter approach, remember to destroy the QTimer object, if any was created, in the destructor of Clock_Application...

Besides that, what exactly is your problem now?

mlong

In
@
void Clock_Application::changeTime()
{
/* do you need to see this function? */
}
@

you should have something like:
@
void Clock_Application::changeTime()
{
QString value = "Whatever the label should be.";

ui->labelWidget->setText(value); // Use whatever you've called your QLabel here instead of "labelWidget"
}
@

It would probably be helpful to see both your changeTime() method and the Clock_Application constructor.

Flurite

[quote author="MuldeR" date="1335219515"]This code excerpt looks okay to me.

Except that you should not create a new QTimer object every time timer_Start() is called. The function may be called several times. Better create the timer object once in the constructor of Clock_Application and destroy it in the destructor of Clock_Application. If you insist to create the QTimer object in timer_Start(), at least set the member variable 'timer' to NULL in the constructor and, if 'timer' is unequal NULL (i.e. an object has been created in a previous call to timer_Start()), destroy the "old" object before you create the new one. Even with the latter approach, remember to destroy the QTimer object, if any was created, in the destructor of Clock_Application...

Besides that, what exactly is your problem now?[/quote]

Thanks for the advice, I will surely take that into account. Anyhow, the errors were as mentioned in a previous post this:

invalid use of incomplete struct type ‘struct Ui::Clock_Application’ --- at line 40
forward declaration of ‘struct Ui::Clock_Application’ --- at line 11
invalid use of incomplete struct type ‘struct Ui::Clock_Application’ --- at line 73
forward declaration of ‘struct Ui::Clock_Application’ --- at line 11,

Lines 40 and 73 are lines in my changeValue() method that try and access the widget.. not surprising lol..

[quote author="mlong" date="1335219613"]In
@
void Clock_Application::changeTime()
{
/* do you need to see this function? */
}
@

you should have something like:
@
void Clock_Application::changeTime()
{
QString value = "Whatever the label should be.";

ui->labelWidget->setText(value); // Use whatever you've called your QLabel here instead of "labelWidget"
}
@

It would probably be helpful to see both your changeTime() method and the Clock_Application constructor.

[/quote]

Sure thing!

This is my changeValue() method:

@
void Clock_Application::changeTime()
{
std::vector<int> times;
QRegExp findTimeSequences("(\d+)");
QString currentTime(ui->Output->text());

int posOffset(0);
while ((posOffset = findTimeSequences.indexIn(currentTime, posOffset)) != -1)
{
    times.push_back(findTimeSequences.cap(1).toInt());
    posOffset += findTimeSequences.matchedLength();
}

times[2] += 1;

QString outputTime;
for (int i = (int) times.size() - 1; i >= 0; i--)
{
    if (times[i] == 60 && i > 0)
    {
        times[i-1] += 1;
        times[i] = 0;
    }

    QString currentNum; currentNum.setNum(times[i]);
    if (times[i] <= 9 && i >= 0)
    {
        currentNum.insert(0, QString("0"));
    }
    if (i < 2)
    {
        currentNum.append(":");
    }

    outputTime.insert(0, currentNum);
}

ui->Output->setText(outputTime);

}
@

This is my constructor (nothing changed to what I am aware of from the original):

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

Thanks for all the help so far, by the way!

MuldeR

[quote author="Flurite" date="1335222560"]
Anyhow, the errors were as mentioned in a previous post this:

invalid use of incomplete struct type ‘struct Ui::Clock_Application’ --- at line 40
forward declaration of ‘struct Ui::Clock_Application’ --- at line 11
invalid use of incomplete struct type ‘struct Ui::Clock_Application’ --- at line 73
forward declaration of ‘struct Ui::Clock_Application’ --- at line 11,

Lines 40 and 73 are lines in my changeValue() method that try and access the widget.. not surprising lol..[/quote]

There are different methods to use the .ui files generated with Qt Designer:
http://doc-snapshot.qt-project.org/4.8/designer-using-a-ui-file.html

It seems that you have decided for the "Using a Pointer Member Variable" method:
http://doc-snapshot.qt-project.org/4.8/designer-using-a-ui-file.html#using-a-pointer-member-variable

However it seems like you are missing to include the header file (.h) generated by the UIC.
You have the forward declaration (probably in your header file), but are missing the actual definition!
Make sure you include the header file generated by UIC in your source file...

Flurite

[quote author="MuldeR" date="1335223272"]
[quote author="Flurite" date="1335222560"]
Anyhow, the errors were as mentioned in a previous post this:

invalid use of incomplete struct type ‘struct Ui::Clock_Application’ --- at line 40
forward declaration of ‘struct Ui::Clock_Application’ --- at line 11
invalid use of incomplete struct type ‘struct Ui::Clock_Application’ --- at line 73
forward declaration of ‘struct Ui::Clock_Application’ --- at line 11,

Lines 40 and 73 are lines in my changeValue() method that try and access the widget.. not surprising lol..[/quote]

There are different methods to use the .ui files generated with Qt Designer:
http://doc-snapshot.qt-project.org/4.8/designer-using-a-ui-file.html

It seems that you have decided for the "Using a Pointer Member Variable" method:
http://doc-snapshot.qt-project.org/4.8/designer-using-a-ui-file.html#using-a-pointer-member-variable

However it seems like you are missing to include the header file (.h) generated by the UIC.
You have the forward declaration (probably in your header file), but are missing the actual definition!
Make sure you include the header file generated by UIC in your source file...[/quote]

No wait, you're saying that I did not include the header file in my clock_application.cpp file? I think I did include that. These are the files I have included in my clock_application.cpp file:

#include "clock_application.h"
#include "ui_clock_application.h"
#include "QString"
#include "QRegExp"
#include "vector"
#include "QThread"

MuldeR

“ui_clock_application.h” is what the UIC created from your .UI file, right?

Did you inspect that file? In you case it should contain:

@/********************************************************************************
** Form generated from reading UI file 'Clock_Application.ui'
**
** Created: Sun 22. Apr 02:04:07 2012
** by: Qt User Interface Compiler version 4.8.1
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/

...

QT_BEGIN_NAMESPACE

class Ui_Clock_Application
{
public:

....

}

namespace Ui {
class Clock_Application: public Ui_Clock_Application {};
}@

If that header file does not define Ui::Clock_Application, then that explains why you get the error.

Flurite

I do not know. It's included in the .cpp file, but I cannot find it in the project's folder.

MuldeR

Actually your compiler would throw an error, if you include a file that does not exist.

So it has to exist - somewhere.

If you create GUI's with the Qt Designer, you first get a .UI file. But C++ doesn't know anything about .UI files.

The UIC program needs to be used to create a C++ header file (.h) from your UI file.

Then the header file created by UIC can be included. It contains the required definitions, of Ui::MyDialgClass.

In your case, it should contain the definition of Ui::Clock_Application. Otherwise you have a problem...

Flurite

Hmm.. I'm positive that I used Qt Designer.. but I'm somehow doubting that's the problem because my program will run if I reset it to what it originally was.

clock_application.h contains my definition of Clock_Application

MuldeR

Defining your own class is not sufficient.

Somehow the code generated by UIC (based on your .UI file from the Qt Designer) needs to be incorporated.

And Qt offers different ways to do that. You apparently chose the "Using a Pointer Member Variable" way.

Please carefully read:
http://doc-snapshot.qt-project.org/4.8/designer-using-a-ui-file.html