QNotifiedProperty: pass old value to callback if requested

Check at compile time whether the static callback takes an argument
(which has to be of the same time as the type of the property). If so,
retrieve the old value and pass it to the callback.

Change-Id: Ib1c4c9e05b826b6be492b03f66fa72ad015963ee
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 22 insertions, 0 deletions

diff --git a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
index e606d121ec..7200bf176e 100644
--- a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
+++ b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
@@ -72,6 +72,7 @@ private slots:
     void multipleObservers();
     void propertyAlias();
     void notifiedProperty();
+    void notifiedPropertyWithOldValueCallback();
 };
 
 void tst_QProperty::functorBinding()
@@ -779,6 +780,15 @@ struct ClassWithNotifiedProperty
     QNotifiedProperty<int, &ClassWithNotifiedProperty::callback> property;
 };
 
+struct ClassWithNotifiedProperty2
+{
+    QVector<int> recordedValues;
+
+    void callback(int oldValue) { recordedValues << oldValue; }
+
+    QNotifiedProperty<int, &ClassWithNotifiedProperty2::callback> property;
+};
+
 void tst_QProperty::notifiedProperty()
 {
     ClassWithNotifiedProperty instance;
@@ -854,6 +864,18 @@ void tst_QProperty::notifiedProperty()
     QCOMPARE(subscribedCount, 10);
 }
 
+void tst_QProperty::notifiedPropertyWithOldValueCallback()
+{
+    ClassWithNotifiedProperty2 instance;
+    instance.property.setValue(&instance, 1);
+    instance.property.setBinding(&instance, [](){return 2;});
+    instance.property.setBinding(&instance, [](){return 3;});
+    instance.property.setValue(&instance, 4);
+    QVector<int> expected {0, 1, 2, 3};
+    QCOMPARE(instance.recordedValues, expected);
+    QCOMPARE(instance.property.value(), 4);
+}
+
 QTEST_MAIN(tst_QProperty);
 
 #include "tst_qproperty.moc"