Handle QProperty inside bindings

If we have a binding containing QProperties, and the binding target is
an old style binding, still we have to trigger an update if any of the
captured properties changes. We cannot reuse the
QQmlJavaScriptExpressionGuards as those depend on Qt's signals, and a
QProperty is not associated with a change signal in the general case.
Therefore, we introduce a new list of QPropertyChangeHandler, which when
triggered cause a reevaluation of the binding.
As an optimization, we skip the whole capturing process for
QQmlPropertyBinding, as that one already takes care of updating itself.

Reverts 845bbb99a41a3e4f05c2b3d05d6db748c825dca0 (because skipping the
capture is only possible when _both_ the bindee and the property in the
binding are QProperty based.)

Change-Id: Iafed2a41dcd708bcc33912ce810d803949379c63
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlengine_p.h b/src/qml/qml/qqmlengine_p.h
index f8b8b187a5..1f513ef8cc 100644
--- a/src/qml/qml/qqmlengine_p.h
+++ b/src/qml/qml/qqmlengine_p.h
@@ -81,6 +81,8 @@
 #include <private/qjsengine_p.h>
 #include <private/qqmldirparser_p.h>
 
+#include <qproperty.h>
+
 QT_BEGIN_NAMESPACE
 
 class QQmlContext;
@@ -125,6 +127,18 @@ public:
     QQmlJavaScriptExpressionGuard *next;
 };
 
+struct QPropertyChangeTrigger {
+    QQmlJavaScriptExpression * m_expression;
+    void operator()();
+};
+
+struct TriggerList : QPropertyChangeHandler<QPropertyChangeTrigger> {
+    TriggerList(QPropertyChangeTrigger trigger) : QPropertyChangeHandler<QPropertyChangeTrigger>(trigger) {};
+    TriggerList *next = nullptr;
+    QObject *target = nullptr;
+    int propertyIndex = 0;
+};
+
 class Q_QML_PRIVATE_EXPORT QQmlEnginePrivate : public QJSEnginePrivate
 {
     Q_DECLARE_PUBLIC(QQmlEngine)
@@ -140,6 +154,7 @@ public:
     QQmlPropertyCapture *propertyCapture;
 
     QRecyclePool<QQmlJavaScriptExpressionGuard> jsExpressionGuardPool;
+    QRecyclePool<TriggerList> qPropertyTriggerPool;
 
     QQmlContext *rootContext;