System.Windows.Controls.AutoCompleteBox.RefreshView C# (CSharp) Method

        private void RefreshView()
        {
            if(_items == null)
            {
                ClearView();
                return;
            }

            // Cache the current text value
            string text = Text ?? string.Empty;

            // Determine if any filtering mode is on
            bool stringFiltering = TextFilter != null;
            bool objectFiltering = FilterMode == AutoCompleteFilterMode.Custom && TextFilter == null;

            int viewIndex = 0;
            int viewCount = _view.Count;
            List<object> items = _items;
            foreach(object item in items)
            {
                bool inResults = !(stringFiltering || objectFiltering);
                if(!inResults)
                {
                    inResults = stringFiltering ? TextFilter(text, FormatValue(item)) : ItemFilter(text, item);
                }

                if(viewCount > viewIndex && inResults && _view[viewIndex] == item)
                {
                    // Item is still in the view
                    viewIndex++;
                }
                else if(inResults)
                {
                    // Insert the item
                    if(viewCount > viewIndex && _view[viewIndex] != item)
                    {
                        // Replace item
                        // Unfortunately replacing via index throws a fatal 
                        // Cost: O(n) vs O(1)
                        _view.RemoveAt(viewIndex);
                        _view.Insert(viewIndex, item);
                        viewIndex++;
                    }
                    else
                    {
                        // Add the item
                        if(viewIndex == viewCount)
                        {
                            // Constant time is preferred (Add).
                            _view.Add(item);
                        }
                        else
                        {
                            _view.Insert(viewIndex, item);
                        }
                        viewIndex++;
                        viewCount++;
                    }
                }
                else if(viewCount > viewIndex && _view[viewIndex] == item)
                {
                    // Remove the item
                    _view.RemoveAt(viewIndex);
                    viewCount--;
                }
            }

            // Clear the evaluator to discard a reference to the last item
            if(_valueBindingEvaluator != null)
            {
                _valueBindingEvaluator.ClearDataContext();
            }
        }