Fix enum loading bug

Excel_UI/Addin/AddIn_Formulas.cs

@@ -36,6 +36,8 @@
 using BH.UI.Excel.Components;
 using BH.oM.Versioning;
 
+using BH.Engine.Serialiser;
+
 namespace BH.UI.Excel
 {
     public partial class AddIn : IExcelAddIn
@@ -134,6 +136,8 @@ public static void RestoreFormulas()
                         if (choice is IObject)
                             IAddObject(choice);
                     }
+
+                    UpdateEnumValues(valueList.MultiChoiceCaller.SelectedItem.ToJson());
                 }
             }
         }
@@ -143,6 +147,93 @@ public static void RestoreFormulas()
         /**** Private Methods                   ****/
         /*******************************************/
 
+        private static void UpdateEnumValues(string collectionName)
+        {
+            //Update enum values in case they have changed since the last serialisation
+            var enumType = BH.Engine.Serialiser.Convert.FromJson(collectionName) as Type; //To strip out the 'BHoM_Version'
+            if (!enumType.IsEnum)
+                return; //This method is only for enum dropdowns, not datasets, etc.
+
+            var nameOfEnum = enumType.Namespace + "." + enumType.Name;
+            var enumChoices = System.Enum.GetValues(enumType);
+
+            // Get the data sheet
+            Worksheet choicesSheet = AddIn.Sheet("BHoM_ChoicesHidden", true, true);
+            if (choicesSheet == null)
+                return;
+
+            // Try to find the list of choices in the spreadsheet
+            int i = 0;
+            while (i++ < 1000) // Just for safety
+            {
+                try
+                {
+                    string name = choicesSheet.Cells[i, 1].Value as string;
+                    if (string.IsNullOrEmpty(name))
+                    {
+                        // Need to add the choices here - this should not be needed on loading a sheet, but as a safety net
+                        choicesSheet.Cells[i, 1].Value = collectionName;
+                        for (int j = 0; j < enumChoices.Length; j++)
+                            choicesSheet.Cells[i, j + 2].Value = enumChoices.GetValue(j).ToString();
+                        break;
+                    }
+                    else
+                    {
+                        var sheetEnumName = BH.Engine.Serialiser.Convert.FromJson(name) as Type;
+                        var sheetNameObject = sheetEnumName.Namespace + "." + sheetEnumName.Name;
+                        if (sheetNameObject == nameOfEnum)
+                            break;
+                    }
+                }
+                catch
+                {
+                    break;
+                }
+            }
+
+            // Obtain the range
+            Range range = choicesSheet.Range[choicesSheet.Cells[i, 2], choicesSheet.Cells[i, enumChoices.Length + 1]];
+
+            //Update the enum values - this is in case an enum value that previously existed has been renamed, so not just checking for null elements
+            for(int x = 0; x < enumChoices.Length; x++)
+                range[1, (x + 1)] = enumChoices.GetValue(x).ToString();
+
+            var rangeValidationFormula = $"=BHoM_ChoicesHidden!{range.Address}";
+            var rangeStart = $"=BHoM_ChoicesHidden!$B${i}:";
+
+            //Update all existing validation items to use the new range
+            Workbook workbook = ActiveWorkbook();
+            if (workbook != null)
+            {
+                foreach (Worksheet sheet in workbook.Sheets.OfType<Worksheet>().Where(x => x.Visible == XlSheetVisibility.xlSheetVisible))
+                {
+                    foreach(Range cell in sheet.UsedRange)
+                    {
+                        Validation validation = cell.Validation;
+                        if(validation != null)
+                        {
+                            try
+                            {
+                                string f1 = validation.Formula1;
+                                string f2 = validation.Formula2;
+                                if(f1.StartsWith(rangeStart) || f2.StartsWith(rangeStart))
+                                {
+                                    validation.Delete();
+                                    validation.Add(XlDVType.xlValidateList, XlDVAlertStyle.xlValidAlertWarning, XlFormatConditionOperator.xlBetween, rangeValidationFormula, Type.Missing);
+                                    validation.InCellDropdown = true;
+                                    validation.IgnoreBlank = true;
+                                }
+                            }
+                            catch
+                            {
+                                //If the validation isn't null, but a property is, that indicates the cell did not have validation in the first place, so no need to do anything with the catch, just ignore the cell
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
         private static void SaveCallerToHiddenSheet(CallerFormula caller)
         {
             // Get the hidden worksheet