View source for Private QObject API

There are certain QObject macros and conventions that are for use in private Qt APIs only. This page describes them.

==Q_PRIVATE_PROPERTY==

Introduced [https://git-service.ait.ac.at/svs-lgpl/qt-4-for-sma-annotator/commit/78e1a866ba5d594233db80f7aab88331db237d3a here].

This macro is used when you have a C++ class that is public that exposes a property whose type is not public. For example, [http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/items/qquickitem.h?id=b1243b8c9ea0add1b7548428c8b0fcb8ee3ac71a#n121 QQuickItem] is a public C++ class that exposes an [http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/items/qquickitem.h?id=b1243b8c9ea0add1b7548428c8b0fcb8ee3ac71a#n121 anchors property], whose type is the [http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/items/qquickanchors_p.h?id=b1243b8c9ea0add1b7548428c8b0fcb8ee3ac71a private QQuickAnchors class]:

    Q_PRIVATE_PROPERTY(QQuickItem::d_func(), QQuickAnchors * anchors READ anchors DESIGNABLE false CONSTANT FINAL)

In this case, the macro expects there to be a getter named anchors() in the type returned by QQuickItem::d_func(), [http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/items/qquickitem_p.h?id=b1243b8c9ea0add1b7548428c8b0fcb8ee3ac71a#n395 which there is]:

    QQuickAnchors *anchors() const;

When using this macro, it's necessary to [http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/items/qquickitem.cpp?id=b1243b8c9ea0add1b7548428c8b0fcb8ee3ac71a#n8687 include the generated moc file] at the end of the corresponding .cpp file:

    QT_END_NAMESPACE
    
    // ...
    
    #include "moc_qquickitem_p.cpp"

If you don't do this, you may see an error like the following (example taken from another class -- replace popup with item and it's the same error):

    [...] moc_qquickpopup_p.cpp
    .moc\debug\moc_qquickpopup_p.cpp(1069): error C2027: use of undefined type 'QQuickPopupPrivate'
    c:\dev\qt5-dev-d\qtquickcontrols2\src\quicktemplates2\.moc\debug\../../../../../../qt5-dev/qtquickcontrols2/src/quicktemplates2/qquickpopup_p.h(71): note: see declaration of 'QQuickPopupPrivate'
    .moc\debug\moc_qquickpopup_p.cpp(1069): error C2227: left of '->anchors' must point to class/struct/union/generic type

==Q_PRIVATE_SLOT==

Similar to Q_PRIVATE_PROPERTY, Q_PRIVATE_SLOT is used when you have a slot in a private class that you want to be considered part of the API of the corresponding public class, without affecting the interface (and hence binary compatibility) of that public class. Using QQuickItem as an example again, Q_PRIVATE_SLOT is used to declare this private slot in [http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/items/qquickitem.h?id=b1243b8c9ea0add1b7548428c8b0fcb8ee3ac71a#n455 qquickitem.h]:

    private:
        Q_PRIVATE_SLOT(d_func(), void _q_resourceObjectDeleted(QObject *))

The slot itself is declared in [http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/items/qquickitem_p.h?id=b1243b8c9ea0add1b7548428c8b0fcb8ee3ac71a#n313 qquickitem_p.h]:

    void _q_resourceObjectDeleted(QObject *);
 
[[Category:Developing Qt]]
[[Category:MOC]]