Ensure dataChanged doesn't force request for unwanted data in QML views.

If a model emits dataChanged() every role was be updated, rather than
just the roles required.  Now only roles which have been used are updated.

Task-number: QTBUG-12598
Reviewed-by: Michael Brasser
(cherry picked from commit b7702b2dcbc36f81759dea0ad74fb19e97b2358f)

2 files changed, 13 insertions, 0 deletions

diff --git a/src/declarative/util/qdeclarativeopenmetaobject.cpp b/src/declarative/util/qdeclarativeopenmetaobject.cpp
index ba5d534..40485bd 100644
--- a/src/declarative/util/qdeclarativeopenmetaobject.cpp
+++ b/src/declarative/util/qdeclarativeopenmetaobject.cpp
@@ -161,6 +161,12 @@ public:
         prop.second = true;
     }
 
+    inline bool hasData(int idx) const {
+        if (idx >= data.count())
+            return false;
+        return data[idx].second;
+    }
+
     bool autoCreate;
     QDeclarativeOpenMetaObject *q;
     QAbstractDynamicMetaObject *parent;
@@ -295,6 +301,12 @@ void QDeclarativeOpenMetaObject::setValue(const QByteArray &name, const QVariant
     activate(d->object, id + d->type->d->signalOffset, 0);
 }
 
+// returns true if this value has been initialized by a call to either value() or setValue()
+bool QDeclarativeOpenMetaObject::hasValue(int id) const
+{
+    return d->hasData(id);
+}
+
 void QDeclarativeOpenMetaObject::setCached(bool c)
 {
     if (c == d->cacheProperties || !d->type->d->engine)
diff --git a/src/declarative/util/qdeclarativeopenmetaobject_p.h b/src/declarative/util/qdeclarativeopenmetaobject_p.h
index 9bb4c34..c18fa3d 100644
--- a/src/declarative/util/qdeclarativeopenmetaobject_p.h
+++ b/src/declarative/util/qdeclarativeopenmetaobject_p.h
@@ -91,6 +91,7 @@ public:
     void setValue(int, const QVariant &);
     QVariant &operator[](const QByteArray &);
     QVariant &operator[](int);
+    bool hasValue(int) const;
 
     int count() const;
     QByteArray name(int) const;