Subclass from Qt Ui Form Class, invalid use of incomplete type

[HappyCoder]

Hi,

i have a base class like this.
ui_calib_base.h

namespace Ui {
class ui_calib_base;
}
 
class ui_calib_base : public QWidget
{
    Q_OBJECT
 
public:
    explicit ui_calib_base(QWidget *parent = 0);
    ~ui_calib_base();
 
protected:
    Ui::ui_calib_base *ui;
}

namespace Ui {
class ui_calib_base;
}

class ui_calib_base : public QWidget
{
    Q_OBJECT

public:
    explicit ui_calib_base(QWidget *parent = 0);
    ~ui_calib_base();

protected:
    Ui::ui_calib_base *ui;
}

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ui_calib_base.cpp

ui_calib_base::ui_calib_base(QWidget *parent) : QWidget(parent), ui(new Ui::ui_calib_base)
{
    ui->setupUi(this);
    ui->tabWidget->setCurrentIndex(0);
}

ui_calib_base::ui_calib_base(QWidget *parent) : QWidget(parent), ui(new Ui::ui_calib_base)
{
    ui->setupUi(this);
    ui->tabWidget->setCurrentIndex(0);
}

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I have moved the ui pointer to protected.

My derived class looks like this:

calib_analog.h

#include <QObject>
#include <QWidget>
 
#include <ui/ui_calib_base.h>
 
class calib_analog : public ui_calib_base
{
    Q_OBJECT
public:
    explicit calib_analog(QWidget *parent = 0);
 
signals:
 
public slots:
};

#include <QObject>
#include <QWidget>

#include <ui/ui_calib_base.h>

class calib_analog : public ui_calib_base
{
    Q_OBJECT
public:
    explicit calib_analog(QWidget *parent = 0);

signals:

public slots:
};

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calib_analog.cpp

#include "calib_analog.h"
 
calib_analog::calib_analog(QWidget *parent) : ui_calib_base(parent)
{
    ui->tabWidget->setCurrentIndex(0);  // this gives the error
}

#include "calib_analog.h"

calib_analog::calib_analog(QWidget *parent) : ui_calib_base(parent)
{
    ui->tabWidget->setCurrentIndex(0);  // this gives the error
}

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I'm not able to get access to the ui pointer in my derived class. I got the error
"invalid use of incomplete type 'class Ui::ui_calib_base'
forward declaration of 'class Ui::ui_calib_base'

I have move the ui pointer to protected, but have no access to it in my derived class? What i'm doing wrong?
Thx