Hello Teodosia,

thanks for your quick response. In fact I can reproduce the issue with your attached project without having to introduce a true custom class.

The issue is actually not a broken UI but broken UI automation. UI Automation is what tools like TestComplete and others are using to run automated UI tests. I could verify the issue using the Inspect tool from the windows SDK (for example here: C:\Program Files (x86)\Windows Kits\10\bin\<version>\x64\inspect.exe).

The first screenshot shows the output of the Inspect tool when the creation filter is active:

My focus is on the Monday item of the drop down and the Inspect tool shows that this item is offscreen, thus it is not showing a highlight to indicate that the item is accessible for UI automation.

In a next step I commented out the creation filter and get this situation:

Here the monday item has a highlight and the offscreen property is set to false. 

As I have mentioned above I assume the bounds of the Accessibility object of these ValueListItemUIElements are not properly initialized - but I have no clue how I would do this.

BTW, one modification I had to make to your project was to use Infragistics 11.2 because that's the version we are still on. Other than that your code is unmodified.

Thanks in advance for your help in this matter.

Best regards

Uwe

I took a look at the ResolveValueListItemAppearance method and it has not changed a lot since 11.2. There are a number of places in this code where it might be conceivable that there would be a NullReferenceException. We could probably tighten it up a bit, but of course that would only happen in the latest release, so that wouldn't help you in v11.2. 

Sounds like maybe you are responding to the selection of a ValueList item and doing something (showing a dialog) that is forcing the ValueList to close while it's in the middle of painting or something like that. That's a pretty common scenario for exception like this to occur.

But if that was the issue, then is seems like replacing the UIElement ONCE and re-using it should be a good solution and there's really no reason for you to keep replacing it every time like the sample here was doing. This will actually be more efficient, anyway.

Hi Mike - while I confirmed that your code fixes the automation it will not fix my problem because it effectively NEVER replaces the UIItems with the subclassed ones because of an error in the logic in your code. With your code my debugger never breaks in the section where you create a new instance. So the behavior is like the creation filter didn't exist. I think the code should look like this instead:

...

                        // Try to find an existing MyValueListItemUIElement and re-use it if possible.
                        MyValueListItemUIElement newValueListItemUIElement = parent.GetDescendant(typeof(MyValueListItemUIElement), valueListItemUIElement.ValueListItem) as MyValueListItemUIElement;
                        
                        // only create new UI item if we didn't find a subclassed one
                        if (newValueListItemUIElement == null)                            
                        {
                            newValueListItemUIElement = new MyValueListItemUIElement(
                                           parent as ValueListItemContainerUIElement,
                                           valueListItemUIElement.ValueListItem,
                                           valueListItemUIElement.IsMruItem,
                                           valueListItemUIElement.ListIndex)
                            {
                                Rect = valueListItemUIElement.Rect
                            };
                        }

                        // replace with existing or new ui item
                        parent.ChildElements.RemoveAt(i);
                        parent.ChildElements.Insert(i, newValueListItemUIElement);


...

However, once I come back to actually replacing the items IU automation no longer works (i.e. Inspect no longer highlights the items in the drop down). So it looks like the journey is not yet over ...

Yes, I see my mistake there. Sorry about that. 

This doesn't work because by the time AfterCreateChildElements has fired, the parent element is throwing away the existing MyValueListItemUIElement, and putting a regular ValueListItemUIElement in it's place. So your creation filter ends up swapping them out again. The code I put in to find an existing one never finds it, because it's already been removed. 

So I think we can get around this by caching the MyValueListItemUIElements in the CreationFilter. 

    public class ValueItemsCreationFilter : IUIElementCreationFilter
    {
        private Dictionary<ValueListItem, MyValueListItemUIElement> myValueListItemUIElements = new Dictionary<ValueListItem, MyValueListItemUIElement>();

        public void AfterCreateChildElements(UIElement parent)
        {
            if (parent is ValueListItemContainerUIElement)
            {                
                for (int i = parent.ChildElements.Count - 1; i >= 0; i--)
                {
                    var valueListItemUIElement = parent.ChildElements[i] as ValueListItemUIElement;
                    if (valueListItemUIElement != null &&
                        !(valueListItemUIElement is MyValueListItemUIElement))
                    {
                        // Try to find an existing MyValueListItemUIElement and re-use it if possible.
                        var valueListItem = valueListItemUIElement.ValueListItem;                        
                        MyValueListItemUIElement newValueListItemUIElement;
                        bool success = this.myValueListItemUIElements.TryGetValue(valueListItem, out newValueListItemUIElement);
                        if (!success)
                        {
                            newValueListItemUIElement = new MyValueListItemUIElement(
                                           parent as ValueListItemContainerUIElement,
                                           valueListItem,
                                           valueListItemUIElement.IsMruItem,
                                           valueListItemUIElement.ListIndex)
                            {
                                Rect = valueListItemUIElement.Rect
                            };

                            parent.ChildElements.RemoveAt(i);
                            parent.ChildElements.Insert(i, newValueListItemUIElement);
                            myValueListItemUIElements[valueListItem] = newValueListItemUIElement;
                        }
                        else
                        {
                            newValueListItemUIElement.Initialize(
                                valueListItem,
                                valueListItemUIElement.IsMruItem,
                                valueListItemUIElement.ListIndex
                                );
                        }
                    }
                }
                //parent.DirtyChildElements(true);
                var height = parent.ChildElements.Count * parent.ChildElements[0].Rect.Height;
                parent.Rect = new Rectangle(parent.Rect.X, parent.Rect.Y, parent.Rect.Width, height);
            }
        }

        public bool BeforeCreateChildElements(UIElement parent)
        {
            return false;
        }
    }

This seems to work - it only replaces the elements the first time you drop down the list and then doesn't replace them again while the dropdown is open. Unless I made some other logical error.

I don't think you did  - I added tracepoints in my test program and can see that items are created only once and then retrieved when the dropdown is expanded again.

Since the dictionary takes a ValueListItem as a key there shouldn't be an issue with multiple drop downs in the same grid. And the creation filter is per grid instance i.e. multiple grids in an application should not be an issue either.

Looks like this time it's really solved. This issue took me through some ups and downs. I hope this time we can stay on the up level (for a while at least).

Thanks again for your continued help and perseverance in this matter!

One thing you might consider is what to do if the cache gets too big. That could happen, in theory, if you created a lot of new ValueListItems, either in a bunch of different ValueLists, or maybe because you ended up re-creating them for some reason. 

It might not be a terrible idea to trap the grid's CellListDropDown event and call a method on the CreationFilter that clears the cached every time the ValueList drops down - just to be safe. 

Yes - makes sense. And it's easy to do. I just added it to the sample program and it works as expected.