How to get the property type name for custom properties?

Question

In Delphi 2007, I added a new string type to my project:

type
  String40 = string;

This property is used in a class:

type
  TPerson = class
  private
    FFirstName = String40;
  published
    FirstName: string40 read FFirstName write FFirstName;
  end;

During runtime, I want to get the name of the property FirstName by using RTTI. I expect it to be String40:

var
  MyPropInfo: TPropInfo;
  PropTypeName: string;
  MyPerson: TPerson;
begin
  MyPerson := TPerson.Create;
  MyPropInfo := GetPropInfo(MyPerson, 'FirstName')^;
  PropTypeName := MyPropInfo.PropType^.Name;

However, in this example PropTypeName is 'string'. What do I need to do get the correct property type name, 'String40'?

Answer 1

This works in Delphi5

type
  String40 = type string;

As for the rest of your code, to have RTTI available you should

• inherit TPerson from TPersistent or
• use the {$M+} compiler directive for TPerson
• make the Firstname property published

---

Edit: what happens if you compile and run this piece of code?

program Project1;

uses
  Classes,
  typInfo,
  Dialogs,
  Forms;

{$R *.RES}

type
  String40 = type string;
  TPerson = class(TPersistent)
  private
    FFirstName: String40;
  published
    property FirstName: string40 read FFirstName write FFirstName;
  end;

var
  MyPropInfo: TPropInfo;
  PropTypeName: string;
  MyPerson: TPerson;

begin
  Application.Initialize;
  MyPerson := TPerson.Create;
  MyPropInfo := GetPropInfo(MyPerson, 'FirstName')^;
  PropTypeName := MyPropInfo.PropType^.Name;
  ShowMessage(PropTypeName);
end.

Answer 2

You need to do two things:

1. Make the property published.
2. Use the type keyword.

You then get:

type
  String40 = type string;
  TPerson = class
  private
    FFirstName : String40;
  published
    property FirstName: string40 read FFirstName write FFirstName;
  end;

var
  MyPropInfo: PPropInfo;
  PropTypeName: string;
  MyPerson: TPerson;
begin
  MyPerson := TPerson.Create;
  try
    MyPerson.FirstName := 'My first name';
    MyPropInfo := GetPropInfo(MyPerson, 'FirstName');
    if MyPropInfo<>nil then begin
      PropTypeName := MyPropInfo^.PropType^.Name;
      Memo1.Lines.Add(PropTypeName);
    end;
  finally
    MyPerson.FRee;
  end;
end;

Tested in D2009.