Use an "int status" extra parameter in property reading/writing.

When calling qt_metacall with the ReadProperty or WriteProperty, the
data is on argv[0] like it was before, but now the QVariant itself is
on argv[1] and there's an extra parameter in argv[2] which the meta
code can use to indicate result.

This allows QtDBus to process properties much more easily. In the case
of property reading, we need to be able to modify the variant itself,
because copying types when we don't have the data isn't very easy.

As for setting, we need to be able to tell setProperty to return true
or false depending on whether we succeeded in setting the property or
not.

Reviewed-By: Kent Hansen
Reviewed-By: Marius Bugge Monsen

1 files changed, 18 insertions, 5 deletions

diff --git a/src/corelib/kernel/qmetaobject.cpp b/src/corelib/kernel/qmetaobject.cpp
index 71dd5ff..34f580b 100644
--- a/src/corelib/kernel/qmetaobject.cpp
+++ b/src/corelib/kernel/qmetaobject.cpp
@@ -2131,8 +2131,15 @@ QVariant QMetaProperty::read(const QObject *object) const
             return QVariant();
         }
     }
+
+    // the status variable is changed by qt_metacall to indicate what it did
+    // this feature is currently only used by QtDBus and should not be depended
+    // upon. Don't change it without looking into QDBusAbstractInterface first
+    // -1 (unchanged): normal qt_metacall, result stored in argv[0]
+    // changed: result stored directly in value
+    int status = -1;
     QVariant value;
-    void *argv[2] = { 0, &value };
+    void *argv[] = { 0, &value, &status };
     if (t == QVariant::LastType) {
         argv[0] = &value;
     } else {
@@ -2142,8 +2149,8 @@ QVariant QMetaProperty::read(const QObject *object) const
     const_cast<QObject*>(object)->qt_metacall(QMetaObject::ReadProperty,
                                               idx + mobj->propertyOffset(),
                                               argv);
-    if (argv[1] == 0)
-        // "value" was changed
+
+    if (status != -1)
         return value;
     if (t != QVariant::LastType && argv[0] != value.data())
         // pointer or reference
@@ -2201,13 +2208,19 @@ bool QMetaProperty::write(QObject *object, const QVariant &value) const
             return false;
     }
 
-    void *argv[2] = { 0, &v };
+    // the status variable is changed by qt_metacall to indicate what it did
+    // this feature is currently only used by QtDBus and should not be depended
+    // upon. Don't change it without looking into QDBusAbstractInterface first
+    // -1 (unchanged): normal qt_metacall, result stored in argv[0]
+    // changed: result stored directly in value, return the value of status
+    int status = -1;
+    void *argv[] = { 0, &v, &status };
     if (t == QVariant::LastType)
         argv[0] = &v;
     else
         argv[0] = v.data();
     object->qt_metacall(QMetaObject::WriteProperty, idx + mobj->propertyOffset(), argv);
-    return true;
+    return status;
 }
 
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