Add QMetaMethod::fromSignal() function

Given a member function that's a signal, returns the corresponding
QMetaMethod. Inspired by the implementation of the template-based
QObject::connect().

The primary use case for this function is to have an effective and
exact (not subject to shadowing) way of checking whether a known
signal was connected to in reimplementations of
QObject::connectNotify(QMetaMethod), avoiding string comparisons.
Example:

void MyObject::connectNotify(const QMetaMethod &signal)
{
    if (signal == QMetaMethod::fromSignal(&MyObject::mySignal)) {
        // Someone connected to mySignal ...
    }
}

Change-Id: I5e4de434275fe543c004d569dcaa9ceda3442f03
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/auto/corelib/kernel/qmetamethod/tst_qmetamethod.cpp b/tests/auto/corelib/kernel/qmetamethod/tst_qmetamethod.cpp
index b5ab61443c..2858bf64eb 100644
--- a/tests/auto/corelib/kernel/qmetamethod/tst_qmetamethod.cpp
+++ b/tests/auto/corelib/kernel/qmetamethod/tst_qmetamethod.cpp
@@ -56,6 +56,8 @@ private slots:
     void invalidMethod();
 
     void comparisonOperators();
+
+    void fromSignal();
 };
 
 struct CustomType { };
@@ -709,5 +711,30 @@ void tst_QMetaMethod::comparisonOperators()
     }
 }
 
+void tst_QMetaMethod::fromSignal()
+{
+#define FROMSIGNAL_HELPER(ObjectType, Name, Arguments)  { \
+        void (ObjectType::*signal)Arguments = &ObjectType::Name; \
+        const QMetaObject *signalMeta = &ObjectType::staticMetaObject; \
+        QCOMPARE(QMetaMethod::fromSignal(signal), \
+            signalMeta->method(signalMeta->indexOfSignal(QMetaObject::normalizedSignature(#Name #Arguments)))); \
+    }
+
+    FROMSIGNAL_HELPER(MethodTestObject, voidSignal, ())
+    FROMSIGNAL_HELPER(MethodTestObject, voidSignalQString, (const QString&))
+    FROMSIGNAL_HELPER(QObject, destroyed, (QObject*))
+    FROMSIGNAL_HELPER(QObject, objectNameChanged, (const QString &))
+
+    // Inherited from QObject
+    FROMSIGNAL_HELPER(MethodTestObject, destroyed, (QObject*))
+    FROMSIGNAL_HELPER(MethodTestObject, objectNameChanged, (const QString &))
+
+    // Methods that are not signals; fromSignal should return invalid method
+    FROMSIGNAL_HELPER(MethodTestObject, voidSlot, ())
+    FROMSIGNAL_HELPER(QObject, deleteLater, ())
+
+#undef FROMSIGNAL_HELPER
+}
+
 QTEST_MAIN(tst_QMetaMethod)
 #include "tst_qmetamethod.moc"