Accessing the UI ! Help !

[fitzy]

Hi there !

I am trying to change the value of a QProgressBar from a class named anotherClass (not from my gui class, which is guiClass).

It builds, but the resulting build crashes !

Here is the error in QT Creator :

... exited with code -1073741819

... exited with code -1073741819

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=> -1073741819 indicates an access violation in windows. An access violation means your process has tried to access memory (ie dereference a pointer) that does not belong to it.


Here is my code :

class guiClass : public QMainWindow
{
    Q_OBJECT
 
public:
    guiClass(QWidget *parent = 0);
    ~guiClass
    Ui::guiClass *ui;
 
};
 
class anotherClass : public QProgressBar {
 
    Q_OBJECT
 
public:
    anotherClass(QObject* parent);
    void anything();
    guiClass *guiClass;
 
};

class guiClass : public QMainWindow
{
    Q_OBJECT

public:
    guiClass(QWidget *parent = 0);
    ~guiClass
    Ui::guiClass *ui;

};

class anotherClass : public QProgressBar {

    Q_OBJECT

public:
    anotherClass(QObject* parent);
    void anything();
    guiClass *guiClass;

};

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void anotherClass::anything(){
    this->guiClass->ui->progressBar->setValue(80); // THIS IS THE WRONG PART
}

void anotherClass::anything(){
    this->guiClass->ui->progressBar->setValue(80); // THIS IS THE WRONG PART
}

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[Lykurg]

Did you initialize your ui and did you set the pointer guiClass right? Can we see the implementation?

EDIT: why do you don't use signals and slots? Any particular reasons for that. Because your case seems to be classical case for using signals.

[squidge]

Put a BP on the "wrong part" and check the values of guiclass and ui.

You do initialise guiClass in anotherClass don't you?

[fitzy]

.
.
Thank you !

Did you initialize your ui and did you set the pointer guiClass right? Can we see the implementation?

guiClass ::guiClass (QWidget *parent)
    : QMainWindow(parent), ui(new Ui::guiClass )
{
    ui->setupUi(this);
 
 
    //this->ui->progressBar->setValue(80); // IT WORKS, but it is in guiClass    
 
    anotherClass *anotherclass = new anotherClass(this);
    anotherclass->anything();
 
}
 
guiClass ::~guiClass ()
{
    delete ui;
}

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


    //this->ui->progressBar->setValue(80); // IT WORKS, but it is in guiClass    

    anotherClass *anotherclass = new anotherClass(this);
    anotherclass->anything();

}

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

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@Lykurg : I don't use SIGNALS and SLOTS because I don't know how to use them
Moreover, I'd prefer to do it without signals and slots.

@fatjuicymole : what is a BP ?

PS: I'm a beginner.

[squidge]

BP = Breakpoint

Where do you initialise guiClass in anotherClass?

[faldzip]

I don't use SIGNALS and SLOTS because I don't know how to use them

So maybe it is time to learn how to use them. And why you would like not to use signals and slots?

[Lykurg]

guiClass ::guiClass (QWidget *parent)
    : QMainWindow(parent), ui(new Ui::guiClass )
{
    ui->setupUi(this);
 
 
    //this->ui->progressBar->setValue(80); // IT WORKS, but it is in guiClass    
 
    anotherClass *anotherclass = new anotherClass(this);
    anotherclass->anything();
 
}

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


    //this->ui->progressBar->setValue(80); // IT WORKS, but it is in guiClass    

    anotherClass *anotherclass = new anotherClass(this);
    anotherclass->anything();

}

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I knew it! you haven't set the pointer guiClass in anotherClass. So you accessing a null pointer!

class anotherClass : public QProgressBar {
 
    Q_OBJECT
 
public:
    anotherClass(QObject* parent);
    void anything();
    guiClass *guiClass;
    void setBackPointer(guiClass *p) {guiClass = p;} // <- add
 
};
 
// and then
 
guiClass ::guiClass (QWidget *parent)
    : QMainWindow(parent), ui(new Ui::guiClass )
{
    ui->setupUi(this);
    anotherClass *anotherclass = new anotherClass(this);
    anotherclass->setBackPointer(this); // <- add
    anotherclass->anything();
}

class anotherClass : public QProgressBar {
 
    Q_OBJECT
 
public:
    anotherClass(QObject* parent);
    void anything();
    guiClass *guiClass;
    void setBackPointer(guiClass *p) {guiClass = p;} // <- add
 
};

// and then

guiClass ::guiClass (QWidget *parent)
    : QMainWindow(parent), ui(new Ui::guiClass )
{
    ui->setupUi(this);
    anotherClass *anotherclass = new anotherClass(this);
    anotherclass->setBackPointer(this); // <- add
    anotherclass->anything();
}

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you can also use the parent of your constructor for setting the back pointer, but you really should learn signal and sots...

[fitzy]

You're right !
I didn't set the pointer guiClass in anotherClass.

Thank you so much !