Untill now the 2 headers were absent as there is 2 examples of new Lister=Filewalker combination (nested meanwhile so last one jhave no such headers as Filewalkers.cpp with definitions of slots). But after updating it and quiting-opening Qtcraetor -- the Build-Debug menu is inactive again - so I cannot check with new conditions.
Here I provid my current pro file:
Qt Code: 
  1. QT       += core gui
  2.  
  3. greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
  4.  
  5. TARGET = Filewalker2
  6. TEMPLATE = app
  7.  
  8.  
  9. SOURCES += main.cpp Filewalker.cpp  filewalker2.cpp
  10.  
  11. HEADERS  += filewalker2.h Lister.h Filewalker.h
  12.  
  13.  
  14. FORMS    += filewalker2.ui
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The filewalker2.h and filewalker2.cpp were created during the creation of project so could I
delete them, how they influence the my native files? Maybe there is some bad interaction?

#include "filewalker2.h"
#include "ui_filewalker2.h"

Filewalker2::Filewalker2(QWidget *parent) :
QWidget(parent),
ui(new Ui::Filewalker2)
{
ui->setupUi(this);
}

Filewalker2::~Filewalker2()
{
delete ui;
}

and header:
#ifndef FILEWALKER2_H
#define FILEWALKER2_H

#include <QWidget>

namespace Ui {
class Filewalker2;
}

class Filewalker2 : public QWidget
{
Q_OBJECT

public:
explicit Filewalker2(QWidget *parent = 0);
~Filewalker2();

private:
Ui::Filewalker2 *ui;
};

#endif // FILEWALKER2_H