[Development] RFC: RAII for property changes

[Nils Jeisecke]

Hi,

On Wed, Apr 15, 2015 at 11:49 AM, André Somers <andre at familiesomers.nl> wrote:
> That's why I have been working with a RAII implementation to monitor
> property changes for a while now.

This looks like an interesting idea.

Another issue I often have with properties is performance related.
Imagine a model that has more than one filter property. In case that
two properties should be set, it does not make sense to update the
model twice. Adding a special setFilters method with multiple
arguments is no option if you want to use property binding in QML.

So I usually have a private "update" slot and a timer that's restarted
on each property invocation so that the model update will take place
on the next event loop iteration.

That "guard" could have a second parameter specifying a "property
evaluation" slot that is guaranteed to be invoked *once* on the next
event loop iteration. It might be tricky to manage the timer though,
maybe setting a special custom object property
"__<SLOT_NAME>_invoke_timer" storing the timer pointer could help? Or
- to get rid of the expensive timer - a flag could be stored as a
property controlling whether QMetaObject::invoke(this, "<SLOT_NAME>",
Qt::QueuedConnection) should be called - the slot (or a c++11 lambda?)
would have to reset that flag then.

Thinking about this, maybe this functionality should be implemented in
a separate class.

Nils