Fix the API for resetting QAbstractItemModels.

This commit deprecates the QAIM::reset() method, and adds beginResetModel()
and endResetModel() methods, addressing Qt issue 247023.

http://www.qtsoftware.com/developer/task-tracker/index_html?method=entry&id=247023

If models and proxies use QAIM::reset() alone, then proxies will
emit modelAboutToBeReset after its source model is reset. This means that mapToSource
will not behave as expected (Will always return an invalid index) in a slot connected
to modelAboutToBeReset.

The usecase for this is maintaining viewstate (which items are selected, expanded)
when the model is reset. See BrowserWidget::modelChanged here:
http://websvn.kde.org/trunk/KDE/kdepim/akonadi/akonadiconsole/browserwidget.cpp?view=markup

Task-number: 247023
Reviewed-by: Olivier Goffart <ogoffart@trolltech.com>
Merge-request: 1072

2 files changed, 45 insertions, 7 deletions

diff --git a/src/corelib/kernel/qabstractitemmodel.cpp b/src/corelib/kernel/qabstractitemmodel.cpp
index 1c9104a..2175542 100644
--- a/src/corelib/kernel/qabstractitemmodel.cpp
+++ b/src/corelib/kernel/qabstractitemmodel.cpp
@@ -1339,7 +1339,7 @@ void QAbstractItemModelPrivate::columnsRemoved(const QModelIndex &parent,
     \endlist
 
 
-    \sa layoutAboutToBeChanged(), dataChanged(), headerDataChanged(), reset(),
+    \sa layoutAboutToBeChanged(), dataChanged(), headerDataChanged(), modelReset(),
         changePersistentIndex()
 */
 
@@ -2769,7 +2769,25 @@ void QAbstractItemModel::endMoveColumns()
 /*!
     Resets the model to its original state in any attached views.
 
-    The view to which the model is attached to will be reset as well.
+    Use beginResetModel() and endResetModel() instead whenever possible. If usng this method, the modelAboutToBeReset signal will
+    not function as expected through proxy models.
+
+    Use this method only if there is no way to call beginResetModel() before invalidating the model.
+*/
+void QAbstractItemModel::reset()
+{
+    Q_D(QAbstractItemModel);
+    emit modelAboutToBeReset();
+    d->invalidatePersistentIndexes();
+    emit modelReset();
+}
+
+/*!
+    Begins a model reset operation.
+
+    A reset operation resets the model to its current state in any attached views.
+
+    \note Any views attached to this model will be reset as well.
 
     When a model is reset it means that any previous data reported from the
     model is now invalid and has to be queried for again. This also means that
@@ -2779,12 +2797,29 @@ void QAbstractItemModel::endMoveColumns()
     call this function rather than emit dataChanged() to inform other
     components when the underlying data source, or its structure, has changed.
 
-    \sa modelAboutToBeReset(), modelReset()
+    You must call this function before resetting any internal data structures in your model
+    or proxy model.
+
+    \sa modelAboutToBeReset(), modelReset(), endResetModel()
+    \since 4.6
 */
-void QAbstractItemModel::reset()
+void QAbstractItemModel::beginResetModel()
 {
-    Q_D(QAbstractItemModel);
     emit modelAboutToBeReset();
+}
+
+/*!
+    Completes a model reset operation.
+
+    You must call this function after resetting any internal data structure in your model
+    or proxy model.
+
+    \sa beginResetModel()
+    \since 4.6
+*/
+void QAbstractItemModel::endResetModel()
+{
+    Q_D(QAbstractItemModel);
     d->invalidatePersistentIndexes();
     emit modelReset();
 }
@@ -3256,7 +3291,7 @@ bool QAbstractListModel::dropMimeData(const QMimeData *data, Qt::DropAction acti
     This signal is emitted when reset() is called, before the model's internal
     state (e.g. persistent model indexes) has been invalidated.
 
-    \sa reset(), modelReset()
+    \sa beginResetModel(), modelReset()
 */
 
 /*!
@@ -3266,7 +3301,7 @@ bool QAbstractListModel::dropMimeData(const QMimeData *data, Qt::DropAction acti
     This signal is emitted when reset() is called, after the model's internal
     state (e.g. persistent model indexes) has been invalidated.
 
-    \sa reset(), modelAboutToBeReset()
+    \sa endResetModel(), modelAboutToBeReset()
 */
 
 /*!
diff --git a/src/corelib/kernel/qabstractitemmodel.h b/src/corelib/kernel/qabstractitemmodel.h
index b47e4cb..1ca6cbe 100644
--- a/src/corelib/kernel/qabstractitemmodel.h
+++ b/src/corelib/kernel/qabstractitemmodel.h
@@ -293,6 +293,9 @@ protected:
 
     void reset();
 
+    void beginResetModel();
+    void endResetModel();
+
     void changePersistentIndex(const QModelIndex &from, const QModelIndex &to);
     void changePersistentIndexList(const QModelIndexList &from, const QModelIndexList &to);
     QModelIndexList persistentIndexList() const;