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

3 files changed, 23 insertions, 5 deletions

diff --git a/src/declarative/graphicsitems/qdeclarativevisualitemmodel.cpp b/src/declarative/graphicsitems/qdeclarativevisualitemmodel.cpp
index 79c1c43..ceb1961 100644
--- a/src/declarative/graphicsitems/qdeclarativevisualitemmodel.cpp
+++ b/src/declarative/graphicsitems/qdeclarativevisualitemmodel.cpp
@@ -444,6 +444,9 @@ public:
 
     int propForRole(int) const;
     void setValue(int, const QVariant &);
+    bool hasValue(int id) const {
+        return m_meta->hasValue(id);
+    }
 
     void ensureProperties();
 
@@ -1216,11 +1219,13 @@ void QDeclarativeVisualDataModel::_q_itemsChanged(int index, int count,
                 int role = roles.at(roleIdx);
                 int propId = data->propForRole(role);
                 if (propId != -1) {
-                    if (d->m_listModelInterface) {
-                        data->setValue(propId, d->m_listModelInterface->data(idx, QList<int>() << role).value(role));
-                    } else if (d->m_abstractItemModel) {
-                        QModelIndex index = d->m_abstractItemModel->index(idx, 0, d->m_root);
-                        data->setValue(propId, d->m_abstractItemModel->data(index, role));
+                    if (data->hasValue(propId)) {
+                        if (d->m_listModelInterface) {
+                            data->setValue(propId, d->m_listModelInterface->data(idx, QList<int>() << role).value(role));
+                        } else if (d->m_abstractItemModel) {
+                            QModelIndex index = d->m_abstractItemModel->index(idx, 0, d->m_root);
+                            data->setValue(propId, d->m_abstractItemModel->data(index, role));
+                        }
                     }
                 } else {
                     QString roleName;
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;