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Thread: Q_PROPERTY: the example doesn't work!

  1. #1
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    Default Q_PROPERTY: the example doesn't work!

    I am trying to build the example from documentation, but it fails:
    Qt Code:
    1. #include <QtCore>
    2.  
    3. #include <iostream>
    4. using namespace std;
    5.  
    6. class MyClass : public QObject
    7. {
    8. Q_OBJECT
    9. Q_PROPERTY(Priority priority READ priority WRITE setPriority)
    10. Q_ENUMS(Priority)
    11.  
    12. public:
    13. MyClass(QObject *parent = 0)
    14. :QObject(parent)
    15. {
    16.  
    17. };
    18. ~MyClass()
    19. {
    20. cout << "MyClass Destructor"<<endl;
    21. };
    22.  
    23. enum Priority { High, Low, VeryHigh, VeryLow };
    24.  
    25. void setPriority(Priority priority);
    26. Priority priority() const;
    27. };
    28.  
    29.  
    30. int main(int argc, char *argv[])
    31. {
    32. QCoreApplication a(argc, argv);
    33. MyClass megaInst;
    34. return a.exec();
    35. }
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    My VS writes me:
    1>main.obj : error LNK2001: unresolved external symbol "public: virtual struct QMetaObject const * __thiscall MyClass::metaObject(void)const " (?metaObject@MyClass@@UBEPBUQMetaObject@@XZ)
    1>main.obj : error LNK2001: unresolved external symbol "public: virtual void * __thiscall MyClass::qt_metacast(char const *)" (?qt_metacast@MyClass@@UAEPAXPBD@Z)
    1>main.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall MyClass::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@MyClass@@UAEHW4Call@QMetaObject@@HPA PAX@Z)
    How can it be fixed?
    Last edited by jpn; 7th July 2009 at 08:41. Reason: missing [code] tags

  2. #2
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    Default Re: Q_PROPERTY: the example doesn't work!

    Hi!

    Exactly, it's just an example, to give you an idea to how it might work.
    To make this code compile, put the class in a header file and provide definition for the setPriority and priority functions.
    It's not required but it's a good practice to separate declaration from definition, to put the class definition in a separate source file

  3. #3
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    Default Re: Q_PROPERTY: the example doesn't work!

    If you're using QMake then place a "#include main.moc" entry just before the main function, rerun qmake and recompile. By default qmake only scans header files for Q_OBJECT macros.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  4. #4
    Join Date
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    Question Re: Q_PROPERTY: the example doesn't work!

    Hello All,

    Could anybody answer me also. Is the Q_PARAMETER the way to do the following:
    Qt Code:
    1. megaInst.priority = MyClass::VeryHigh;
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    or it always have to be
    Qt Code:
    1. megaInst.setPriority(MyClass::VeryHigh);
    To copy to clipboard, switch view to plain text mode 
    (I mean a variable imitation but not function call). If not, what a purpose of Q_PROPERTY if you have to reach property as function?

    Or is there any other way to do that?

    Thanks

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