Null reference exception in latest DataGrid

After updating to the latest build of WPF Elements 6 a few days ago I ran into a null reference exception in DataGridItemsSource.BuildHierarchModel() when my C# code cleared a binding to the DataGrid.ItemsSource property. This error did not occur in the previous version I had been using (from last August). I was able to resolve the problem with the following change to the source:

    private void BuildHierarchyModel()
{
  HierarchicalDataTemplate template = _itemTemplate as HierarchicalDataTemplate;
  if (template != null)
  {
    Binding binding = template.ItemsSource as Binding;
    if (binding != null)
    {
      DestroyHierarchyModel(); // TODO: rather than destroying the heirarchy model, only reconstruct the parts that changed.
      _hierarchy = new Dictionary<object, DataGridItemWrapper>();
      if (_source != null)          // GPT - Inserted 
      {                         // GPT - Inserted 
          foreach (object o in _source)
          {
              List<object> rawChildren;
              DataGridItemWrapper wrapper = BuildItemWrapper(o, 0);
              IList children = GetChildren(wrapper, o, binding, 1, out rawChildren);
              wrapper.ChildrenChanged += new EventHandler(Wrapper_ChildrenChanged);
              if (children != null && children.Count > 0)
              {
                  wrapper.Children = children;
                  wrapper.SortedChildren = rawChildren;

                  if (HierarchyMode == DataGridHierarchyMode.Expanded)
                  {
                      _hierarchyLock++;
                      wrapper.IsExpanded = true;
                      _hierarchyLock--;
                  }
                  _hierarchyLock++;
                  bool expandedState;
                  bool found = _expansionStates.TryGetValue(wrapper.Object, out expandedState);
                  if (found)
                  {
                      wrapper.IsExpanded = expandedState;
                  }
                  _hierarchyLock--;
              }
          }
      }                 // GPT - Inserted 
    }
  }
}

Hello Peter

Thanks for pointing this out and posting the code fix. This will be updated in the next nightly build.

-Jason Fauchelle

Hi Jason,

Thanks,

Peter