AvalonStudio.ShellViewModel.InvalidateErrors C# (CSharp) Method

        public void InvalidateErrors()
        {
            var allErrors = new List<ErrorViewModel>();
            var toRemove = new List<ErrorViewModel>();
            var hasChanged = false;

            foreach (var document in DocumentTabs.Documents.OfType<EditorViewModel>())
            {
                if (document.Model.CodeAnalysisResults != null)
                {
                    foreach (var diagnostic in document.Model.CodeAnalysisResults.Diagnostics)
                    {
                        var error = new ErrorViewModel(diagnostic);
                        var matching = allErrors.FirstOrDefault(err => err.IsEqual(error));

                        if (matching == null)
                        {
                            allErrors.Add(error);
                        }
                    }
                }
            }

            foreach (var error in ErrorList.Errors)
            {
                var matching = allErrors.SingleOrDefault(err => err.IsEqual(error));

                if (matching == null)
                {
                    toRemove.Add(error);
                }
            }

            foreach (var error in toRemove)
            {
                hasChanged = true;
                ErrorList.Errors.Remove(error);
            }

            foreach (var error in allErrors)
            {
                var matching = ErrorList.Errors.SingleOrDefault(err => err.IsEqual(error));

                if (matching == null)
                {
                    hasChanged = true;
                    ErrorList.Errors.Add(error);
                }
            }

            if (hasChanged)
            {
                BottomTabs.SelectedTool = ErrorList;
            }
        }