<![CDATA[How do those crazy Q Macros work?]]>Hello fellow Qt Devs,

I do not quite understand how the so called "signal" can change value of a property(whatever hides behind that keyword) while there is no visible Object instance.
And what is the "FINAL" custom type meant for in the Q_PROPERTY signature cause it doesn't change the result.
crazy_macros.png

]]>https://forum.qt.io/topic/165056/how-do-those-crazy-q-macros-workRSS for NodeWed, 14 Oct 2026 12:17:18 GMTThu, 03 Sep 2026 14:56:12 GMT60<![CDATA[Reply to How do those crazy Q Macros work? on Fri, 04 Sep 2026 02:52:18 GMT]]>@DSpUz said in How do those crazy Q Macros work?:

there is no visible Object instance.

There IS an object instance! The singleton is an instance.

I do not quite understand how the so called "signal" can change value of a property

A NOTIFY signal tells the QML engine to discard the old (cached) property value and read it again.

When your Globals singleton (instance) emits the numberChanged signal, the QML engine re-reads Globals.number and updates the text.

]]>https://forum.qt.io/post/839967https://forum.qt.io/post/839967Fri, 04 Sep 2026 02:52:18 GMT<![CDATA[Reply to How do those crazy Q Macros work? on Thu, 03 Sep 2026 19:27:39 GMT]]>Hi,

You can find everything around Q_PROPERTY in this chapter of the Qt documentation.

FINAL means that you cannot shadow this property in a subclass.

]]>https://forum.qt.io/post/839958https://forum.qt.io/post/839958Thu, 03 Sep 2026 19:27:39 GMT<![CDATA[Reply to How do those crazy Q Macros work? on Thu, 03 Sep 2026 15:09:38 GMT]]>Apparently the QML_SINGLETON macro the Singleton object is automatically created with default constructor when a QML Engine accesses it so thats why one can call its setters or whatever, at least it is said like that in the next video after the implementation

]]>https://forum.qt.io/post/839955https://forum.qt.io/post/839955Thu, 03 Sep 2026 15:09:38 GMT