Accessing the UI ! Help !

[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...