How do those crazy Q Macros work?

[DSpUz]

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.

[DSpUz]

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

[SGaist]

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.

[JKSH]

@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.