Simplify code using wxDataViewCtrl::m_Deleting in wxOSX

Use a RAII-based helper class to reset this flag automatically on scope
exit instead of doing it manually.

This also ensures that we restore the original value rather than just
resetting it which would be more correct in the (admittedly, very
unlikely) case when any of the functions changing m_Deleting is called
recursively.

include/wx/osx/dataview.h

@@ -259,11 +259,6 @@ public:
   {
     m_CustomRendererPtr = NewCustomRendererPtr;
   }
- // sets the flag indicating a deletion process:
-  void SetDeleting(bool deleting)
-  {
-    m_Deleting = deleting;
-  }
 
   void AdjustAutosizedColumns() const;
 
@@ -305,6 +300,9 @@ private:
                    // after the actual deletion of the item; then, native callback functions/delegates may try to update data of variables that are already deleted;
                    // if this flag is set all native variable update requests will be ignored
 
+  // This class can set (and reset) m_Deleting.
+  friend class wxOSXDVCScopedDeleter;
+
   void* m_cgContext; // pointer to core graphics context
 
   wxDataViewCustomRenderer* m_CustomRendererPtr; // pointer to a valid custom renderer while editing; this class does NOT own the pointer

src/osx/dataview_osx.cpp

@@ -49,6 +49,33 @@ wxString ConcatenateDataViewItemValues(wxDataViewCtrl const* dataViewCtrlPtr, wx
   return dataString;
 }
 
+// ============================================================================
+// wxOSXDVCScopedDeleter
+// ============================================================================
+
+// Helper class which exists only to reset m_Deleting on scope exit.
+class wxOSXDVCScopedDeleter
+{
+public:
+    explicit wxOSXDVCScopedDeleter(wxDataViewCtrl* dvc) :
+        m_dvc(dvc),
+        m_valueOrig(m_dvc->m_Deleting)
+    {
+        m_dvc->m_Deleting = true;
+    }
+
+    ~wxOSXDVCScopedDeleter()
+    {
+        m_dvc->m_Deleting = m_valueOrig;
+    }
+
+private:
+    wxDataViewCtrl* const m_dvc;
+    const bool m_valueOrig;
+
+    wxDECLARE_NO_COPY_CLASS(wxOSXDVCScopedDeleter);
+};
+
 // ============================================================================
 // wxOSXDataViewModelNotifier
 // ============================================================================
@@ -192,42 +219,33 @@ bool wxOSXDataViewModelNotifier::ItemsChanged(wxDataViewItemArray const& items)
 
 bool wxOSXDataViewModelNotifier::ItemDeleted(wxDataViewItem const& parent, wxDataViewItem const& item)
 {
-  bool noFailureFlag;
-
-
   wxCHECK_MSG(item.IsOk(),false,"To be deleted item is invalid.");
  // when this method is called and currently an item is being edited this item may have already been deleted in the model (the passed item and the being edited item have
  // not to be identical because the being edited item might be below the passed item in the hierarchy);
  // to prevent the control trying to ask the model to update an already deleted item the control is informed that currently a deleting process
  // has been started and that variables can currently not be updated even when requested by the system:
-  m_DataViewCtrlPtr->SetDeleting(true);
-  noFailureFlag = m_DataViewCtrlPtr->GetDataViewPeer()->Remove(parent);
- // enable automatic updating again:
-  m_DataViewCtrlPtr->SetDeleting(false);
+  wxOSXDVCScopedDeleter setDeleting(m_DataViewCtrlPtr);
+
+  bool ok = m_DataViewCtrlPtr->GetDataViewPeer()->Remove(parent);
 
   AdjustAutosizedColumns();
- // done:
-  return noFailureFlag;
+
+  return ok;
 }
 
 bool wxOSXDataViewModelNotifier::ItemsDeleted(wxDataViewItem const& parent, wxDataViewItemArray const& WXUNUSED(items))
 {
-  bool noFailureFlag;
-
-
  // when this method is called and currently an item is being edited this item may have already been deleted in the model (the passed item and the being edited item have
  // not to be identical because the being edited item might be below the passed item in the hierarchy);
  // to prevent the control trying to ask the model to update an already deleted item the control is informed that currently a deleting process
  // has been started and that variables can currently not be updated even when requested by the system:
-  m_DataViewCtrlPtr->SetDeleting(true);
+    wxOSXDVCScopedDeleter setDeleting(m_DataViewCtrlPtr);
  // delete all specified items:
-  noFailureFlag = m_DataViewCtrlPtr->GetDataViewPeer()->Remove(parent);
- // enable automatic updating again:
-  m_DataViewCtrlPtr->SetDeleting(false);
+    bool ok = m_DataViewCtrlPtr->GetDataViewPeer()->Remove(parent);
 
   AdjustAutosizedColumns();
- // done:
-  return noFailureFlag;
+
+  return ok;
 }
 
 bool wxOSXDataViewModelNotifier::ValueChanged(wxDataViewItem const& item, unsigned int col)
@@ -251,14 +269,9 @@ bool wxOSXDataViewModelNotifier::ValueChanged(wxDataViewItem const& item, unsign
 
 bool wxOSXDataViewModelNotifier::Cleared()
 {
-  bool noFailureFlag;
-
-  // NOTE: See comments in ItemDeleted method above
-  m_DataViewCtrlPtr->SetDeleting(true);
-  noFailureFlag = m_DataViewCtrlPtr->GetDataViewPeer()->Reload();
-  m_DataViewCtrlPtr->SetDeleting(false);
-
-  return noFailureFlag;
+    // NOTE: See comments in ItemDeleted method above
+    wxOSXDVCScopedDeleter setDeleting(m_DataViewCtrlPtr);
+    return m_DataViewCtrlPtr->GetDataViewPeer()->Reload();
 }
 
 void wxOSXDataViewModelNotifier::Resort()