QNotifiedProperty: Add guard callback

A guard callback is a predicate which takes the new value set by
setValue or computed as the result of a binding expression. If it
returns false, the value is discarded and the old value is kept.
Note that due to lazyness, when setting a binding, we still notify
everyone as the binding is only evaluated on demand, and the guard can
thus only run when someone actually queries the value.
Note further that a guard is allowed to modify the value that is passed
to it (e.g. to clamp it to a certain range).

Task-number: QTBUG-85032
Change-Id: I3551e4357fe5780fb75da80bf8be208ec152dc2a
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

0 files changed, 0 insertions, 0 deletions