Problem description: -------------------- Assume we have two properties, P1 and P2. Assume further that we assign a binding to P2, so that it depends on P1. Let the binding additionally capture some (non-QProperty) boolean, and only create the dependency to P1 if the boolean is true. The state afterwards is P1:[p1vaue|firstObserver] | | v ---[p2binding] / P2:[p2value|binding] If the boolean is set to false, and P1 changes its value, we still correctly re-evaluate the binding and update P2's value. However, during binding evaluation we will notice that there is no further dependency from P2 on P1, and remove its observer. The state afterwards is P1:[p1vaue|firstObserver=nullptr] ---[p2binding] / P2:[p2value|binding] Then, during the notify phase, we traverse the observer's again, starting from P1's firstObserver. Given that it is nullptr now, we never reach P2's binding, and thus won't send a notification from it. Fix: ---- We store a list of all visited binding-observers (in a QVarLengthArray, to avoid allocations as long as possible). After the binding evaluation phase, we then use that list to send notifications from every binding that we visited. As we already have a list of all bindings, we no longer need to recurse on binding-observes during the notification process; instead, we only need to deal with static callbacks and ChangeHandlers. The pre-existing notification logic is still kept for the grouped update case, where we already have a list of all delayed properties, and should therefore not encounter the same issue. Unifying its codepath with the existing logic is left as an exercise for a later patch. Fixes: QTBUG-105204 Task-number: QTBUG-104982 Pick-to: 6.4 6.3 6.2 Change-Id: I2951f7d9597f4da0b8560a64dfb834f7ad86e757 Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org> Reviewed-by: Sami Shalayel <sami.shalayel@qt.io> Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>