Validation of property objects

Hi,

I've couple of general questions on objects and properties for which I could not find any real explanation/documentation. 

• In some examples, objects and properties are initialized in the enumerateObjectInstances method of the Visual. It uses a switch statement to push all the objects and their properties into the VisualObjectInstance[] array. In other examples the enumerateObjectInstances is just left to the default implementation. What is the advantage/disadvantage of these two distinct ways of working ?

• Where and how do you write the code to validate property values? Suppose you have a property for controlling the font size of a label and you want it to be between 10 and 20? I've declared the object and property inside my capabilities file as follows:

  "fontSize" : {
                      "displayName": "Font Size",
                      "type": {
                          "formatting": {
                              "fontSize": true
                          }
                      }
                  }

  Next I wrote the corresponding class in settings.ts 

  module powerbi.extensibility.visual {
      "use strict";
      import DataViewObjectsParser = powerbi.extensibility.utils.dataview.DataViewObjectsParser;
  
      export class TableVisualSettings extends DataViewObjectsParser {
        public tableFormatting: tableFormatting = new tableFormatting();
        }
  
      export class tableFormatting {
        public show: boolean = true;
        public border: boolean = true;
        public backgroundColor: string = "#FFFFFF";
        public fontSize: number = 14;
       }
  }

  I have no trouble accessing the object and it's properties in code but where should the validation code go? And is there a way to display an error message to the user ?

   

   

   Thanks for any help you can provide !