[Solved] Cannot convert QQuickItem to QObject

  • I am using Qt 5.2 beta 1 on windows 8 and have encountered a problem. I followed the example "Interacting with QML Objects from C++":http://qt-project.org/doc/qt-5.1/qtqml/qtqml-cppintegration-interactqmlfromcpp.html
    // Using QQuickView
    QQuickView view;
    QObject *object = view.rootObject(); // <== GENERATES ERROR

    but I get the error message "cannot convert 'QQuickItem' to 'QObject' in initialization" for the last line. Any suggestions?

  • Moderators

    Do a qobject_cast, or use QQuickItem pointer instead of QObject.

  • Thanks. It works when I include <QtQuick> instead of <QtQuick/QQuickView>.

  • Moderators

    You loose compile time by doing that. Since you are now certain the issue is with headers, try to include hard dependencies only:
    #include <QQuickItem>
    #include <QQuickView>

  • That works! Thanks again.

    BTW, Does it matter if I use <QQuickItem> or <QtQuick/QQuickItem>, etc? (I suspect not.)

  • Moderators

    No, not really. Just <QQuickItem> is considered more "portable": if the class is moved to another module in the future (Qt6...) it will still compile. But that is such a minor thing that I won't bother much. It was very useful in Qt4->Qt5 migration, though.

  • Hi guys, thanks SteveG for this post.
    In my case with the same code I obtain those errors:

    • " warning: C4189: 'object' : local variable is initialized but not referenced"

    • "main.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __thiscall QQuickView::~QQuickView(void)" (_imp??1QQuickView@@UAE@XZ) referenced in function _main"

    • "main.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: class QQuickItem * __thiscall QQuickView::rootObject(void)const " (_imp?rootObject@QQuickView@@QBEPAVQQuickItem@@XZ) referenced in function _main"

    • "main.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: void __thiscall QQuickView::setSource(class QUrl const &)" (_imp?setSource@QQuickView@@QAEXABVQUrl@@@Z) referenced in function _main"

    • "main.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: __thiscall QQuickView::QQuickView(class QWindow *)" (_imp??0QQuickView@@QAE@PAVQWindow@@@Z) referenced in function _main"

    • "error: LNK1120: 4 unresolved externals"

    When I use the "qobject_cast" i've got this error: "error: C2065: 'object' : undeclared identifier".

    I don't get what's wrong.

    NB: I am working on Qt 5.1.1 .

  • Woow! After a "Run qmake" and a "Build All" I don't have anymore errors or warnings, it compiles and works.

  • Maybe the ghosts and goblins are working overtime for Halloween. ;-)

  • :) Yeah, next time I'll contact directly the ghostbusters instead to post here.

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