QML property on change ?

fcarney

Look for Q_PROPERTY macros:

Q_PROPERTY(int ted READ ted WRITE setted NOTIFY tedChanged)

Note: the NOTIFY signal can be named anything.

JoeCFD

@fcarney is right. The signal name can be anything. I normally use tedChanged in my app.

lemons

Couldn't vehicle.data also be a struct with a Q_GADGET macro?
→ in this case there might only be a dataChanged signal, instead of a signal for each member of the struct

SPlatten

@lemons , its not my code and I have no say on how it is or was coded.

Drooke

@SPlatten try console.log(vehicle) and console.log(vehicle.data) in a component.oncompleted block. which may print out the classname / QObject type. This may point to the location of your code you're looking for.

GrecKo

To answer the original question :

Is there a way to create an event handler for when a property changes ?

Something like:

property double waterDepth: vehicle.data.totalWaterDepth
onWaterDepthChanges: {
   ...
}

The corresponding change signal would be waterDepthChanged, with its handler being onWaterDepthChanged: ....

Scrolling through your past exchange would make me guess that vehicle has a property data which is a QQmlPropertyMap where the totalWaterDepth is eventually set. Doesn't a global search followed by some code unravelling give you any clues?

But why do you need a signal handler in the first place? It's generally a code smell and should be available when possible (moreso when it's not a boolean property).

SPlatten

@GrecKo , I tried that and it doesn't work, I think because the primitive type double is not an object.

SPlatten

@GrecKo said in QML property on change ?:

QQmlPropertyMap

Thank you, you have given me a helpful hint in that I have now located:

Q_PROPERTY (QQmlPropertyMap *data READ data CONSTANT)

GrecKo

@SPlatten said in QML property on change ?:

@GrecKo , I tried that and it doesn't work, I think because the primitive type double is not an object.

That doesn't prevent it from triggering change signals.

Maybe your vehicle or data is changed in C++ without emitting any NOTIFY signal? if totalWaterDepth is in a QQmlPropertyMap it shouldn't be able to be changed without emitting a signal so that leaves the other two.

How do you know the final value changes?

SPlatten

@GrecKo , I see if update on the QML front end.