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Thread: QWidget: Must construct a QApplication before a QWidget

  1. #1
    Join Date
    Aug 2014
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    Post QWidget: Must construct a QApplication before a QWidget

    Hi all:
    I've got this error in my application when I run in the release mode on Windows( on Ubuntu ,whether in debug or release mode ,there's no problem.And debug mode on Windows is ok). I think this error is related to a C++ library which I used in my application.In the library ,I build a class,which inherit from the QWidget class. And I build another class who is name is XXXmanger ,inherit from the QObject class to manage the widget class .When I try to new the manager class, the app goes wrong.

    Qt Code:
    1. CHistoryFormManager::CHistoryFormManager(QObject *parent) :
    2. CbaseFormManager(parent)
    3. {
    4. d_ptr = new CHistoryFormManagerPrivate;
    5. d_ptr->q_ptr = this;
    6. }
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    This is the construction function of the manager class .
    Qt Code:
    1. class CHistoryFormManagerPrivate
    2. {
    3. CHistoryFormManager * q_ptr;
    4. Q_DECLARE_PUBLIC(CHistoryFormManager)
    6. public:
    8. void addItem();
    9. void deleteItem();
    10. void openItem();
    12. int m_index;
    13. QMenu *m_treeMenu;
    14. QMenu *m_itemMenu;
    15. QAction *m_addFormAction;
    16. QAction *m_deleteFormAction;
    17. QAction *m_openItemAction;
    18. QStandardItem *m_item;
    19. QWidget *m_widget;
    20. QTreeView *m_treePro;
    22. QList<CHistoryForm *> m_formList;
    23. QList<QStandardItem *> m_newedItemList;
    24. QMap<QStandardItem*,CHistoryForm*> m_map;
    26. private:
    28. void createTreeMenu(QWidget * parent); // create tree Menu
    29. void createItemMenu(QWidget * parent); // create Item Menu
    31. void createItemAction(QWidget * parent);
    32. void createTreeAction(QWidget * parent);
    33. };
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    This is the private class of the manager class.
    Please help. Thanks.
    Last edited by wysota; 27th October 2014 at 09:00. Reason: missing [code] tags

  2. #2
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    Default Re: QWidget: Must construct a QApplication before a QWidget

    The error you get is related to instantiating objects and not to defining classes. Most likely you have a static global variable of type derived or containing QWidget or you create a regular object before creating QApplication object, as the error message suggests.
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