Access variable contained in a BPL

Question

I have a system developed in Delphixe3 and I’m starting to modular it. However, another question has arisen. In a Unit that will be in one of the modules, I own:

type 
   TUsuario = record
     id:Integer;
     idEmpresa:Integer;
     usuario:string;
     foto:string;
     validade: TDateTime;
     senha:string;
     nome:string;
     admin:Boolean;
     ultimoAcesso:TDateTime;
     dataCadastro:TDateTime;
   end;

and

var
  usuario:TUsuario;

That at certain times I will feed this variable and in others I will retrieve her information. My question: How to do this?

Updating

---

My system is distributed as follows:

Aplicação - Menu - Login - Package Default (Runtime Package) * Unit TUsuario * Unit FuncoesDefault * Unit FuncoesSeguranca - Package Cadastros (Carregado via LoadPackage) * CD001 - Uma tela de cadastros qualquer

Regarding the error of Access Violation, I am creating the variable inside the package Default, in Unit Funcoesdefault.

In my application, on the login screen, I instantiate the already created variable:

usuario:= TUsuario.Create;

At the Event FormShow form CD001, I call a Function unit Funcoesseguranca, responsible for checking in the database the rights of the user (insert, edit, remove, etc). This Function receives by parameter a string with the screen code and my variable usuario, previously created on the login screen.

Right in the forefront of my Function there is a if usuario.isAdmin to check if the user is an administrator. I already get the error of Access Violation.

Updating

---

Follow an excerpt from my Unit Funcoesdefault

unit FuncoesDefault;

interface

uses
  U_TUsuario;

var
  usuario:TUsuario;

implementation

initialization
  usuario := TUsuario.Create;

end.

Answer 1

First of all, I recommend you abandon the practice of using record and start using class, which is a more modern and much more powerful language construction. To do so, study a little about object-oriented programming, classes, constructor, destructor, methods and properties.

With regard you asked, since the class TUsuario is declared, declare a utility class to operate on these objects, for example TUsuarioRepositorio, which will have a number of methods to recover and save instances of TUsuario. Something like:

type
  TUsuarioRepositorio
  public
    class function UsuarioPorNome(const aNome: string): TUsuario;
    class procedure Salvar(aUsuario: TUsuario);
  end;

so in a certain part of your code you would create a user like this:

var
  novoUsuario: TUsuario;
begin
  ...
  novoUsuario := TUsuario.Create;
  novoUsuario.Nome := 'Huguinho';
  novoUsuario.Senha := 'M@rgar1da';
  novoUsuario.Admin := True;

  TUsuarioRepositorio.Salvar(novoUsuario);
  ...
end;

In this code a class object TUsuario is instantiated, some of its properties are initialized and it is saved somewhere (file or database). Then to recover this same user the code could be:

var
  usuarioProcurado: TUsuario;
  nome: string;
begin
  ...
  nome := 'Huguinho';
  usuarioProcurado := TUsuarioRepositorio.UsuarioPorNome(nome);
  if usuarioProcurado <> nil then
    ShowMessage(Format('O usuário %s tem o Id=%d', [usuarioProcurado.Nome, usuarioProcurado.Id]))
  else
    ShowMessage('Nenhum usuário existe com o nome='+nome); 
  ...
end;

With this work model you separated the object from the code that manipulates the persistence of this object, which is a great practice of programming and design, in addition to allowing a high level of code modularization, as you can place the objects in a package and the repositories in another.

As the idea is modularize you can put the Unit declaring TUsuario (for example, Usuarios.pas) in a package separate. When compiled, the project of this package will generate a file .BPL (for example, SegurancaD17.BPL) and an archive .DCP (SegurancaD17.DCP). The design of this package must be configured to be a Runtime package and the design of your application should indicate at least this as a Runtime package.

On your application it will be enough to do the uses of Unit Usuarios. When compiling your project Delphi will realize that the Unit is in a Runtime package and will generate dependency for it instead of including in the .EXE. When you distribute the .EXE, shall distribute together the SegurancaD17.BPL, the file .DCP is important for the compiler, not the executable.