Allow property observers on readonly properties

This makes it necessary to tolerate evaluate() calls after the engine is
gone. With non-QProperty properties this can't happen as the engine
controls the observers.

Change-Id: Ia700a10ad847b8a174b2346a4ad7a4de7afb0c83
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/qml/qml/qqmlboundsignal.cpp b/src/qml/qml/qqmlboundsignal.cpp
index 0dfbf1faee..665d4e6c75 100644
--- a/src/qml/qml/qqmlboundsignal.cpp
+++ b/src/qml/qml/qqmlboundsignal.cpp
@@ -175,12 +175,16 @@ QString QQmlBoundSignalExpression::expression() const
 // Changes made here may need to be made there and vice versa.
 void QQmlBoundSignalExpression::evaluate(void **a)
 {
-    Q_ASSERT (engine());
-
     if (!expressionFunctionValid())
         return;
 
     QQmlEngine *qmlengine = engine();
+
+    // If there is no engine, we have no way to evaluate anything.
+    // This can happen on destruction.
+    if (!qmlengine)
+        return;
+
     QQmlEnginePrivate *ep = QQmlEnginePrivate::get(qmlengine);
     QV4::ExecutionEngine *v4 = qmlengine->handle();
     QV4::Scope scope(v4);