Hi everyone,
i always get this error when i compile :
'Viewer' has not been declared

My viewer.h and modultreewidget.h are in the same directory.

MODULTREEWIDGET:
Qt Code: 
  1. #ifndef MODULTREEWIDGET_H
  2. #define MODULTREEWIDGET_H
  3.  
  4. #include <QWidget>
  5. #include <QTreeWidget>
  6. #include <QTimer>
  7. #include "viewer.h"
  8. #include "basewidget.h"
  9.  
  10. class ModulTreeWidget : public QTreeWidget
  11. {
  12.     Q_OBJECT
  13. public:
  14.     explicit ModulTreeWidget(QTreeWidget *parent=0,Viewer *v=0);
  15.     ~ModulTreeWidget();
  16.     void addModule(BaseWidget *b);
  17. public slots:
  18.     void startPresentation();
  19.     void showNext();
  20. private:
  21.     std::vector<BaseWidget*> baseWidgets;
  22.     int count;
  23.     int currentId;
  24. };
  25.  
  26. #endif // MODULTREEWIDGET_H
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VIEWER:
Qt Code: 
  1. #ifndef VIEWER_H
  2. #define VIEWER_H
  3.  
  4. #include <QMainWindow>
  5. #include <QWidget>
  6. #include <QVBoxLayout>
  7. #include <QLabel>
  8. #include <QDebug>
  9. #include <QStringList>
  10. #include <QInputDialog>
  11. #include <QString>
  12. #include <QMessageBox>
  13. #include <QVector>
  14. #include <QListWidget>
  15. #include <QListWidgetItem>
  16. #include <QTableWidgetItem>
  17. #include <QList>
  18. #include <QItemSelectionModel>
  19. #include <QModelIndexList>
  20. #include "basewidget.h"
  21. #include "tabledialog.h"
  22. #include <QTreeWidget>
  23. #include <QTreeWidgetItem>
  24. #include <vector>
  25. #include <QDesktopWidget>
  26. #include <QColorDialog>
  27. #include "modultreewidget.h"
  28.  
  29. namespace Ui {
  30. class Viewer;
  31. }
  32.  
  33. class Viewer : public QMainWindow
  34. {
  35.     Q_OBJECT
  36.  
  37. public:
  38.     explicit Viewer(QWidget *parent = 0);
  39.     ~Viewer();
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What´s the problem?