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>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/corelib/kernel/qpropertyprivate.h b/src/corelib/kernel/qpropertyprivate.h
index 43318f25c0..145f2c66b9 100644
--- a/src/corelib/kernel/qpropertyprivate.h
+++ b/src/corelib/kernel/qpropertyprivate.h
@@ -84,7 +84,8 @@ public:
 
     QUntypedPropertyBinding setBinding(const QUntypedPropertyBinding &newBinding,
                                        void *propertyDataPtr, void *staticObserver = nullptr,
-                                       void (*staticObserverCallback)(void *, void *) = nullptr);
+                                       void (*staticObserverCallback)(void *, void *) = nullptr,
+                                       bool (*guardCallback)(void *, void *) = nullptr);
     QPropertyBindingPrivate *binding();
 
     void evaluateIfDirty();