Why is my global variable "inaccessible" when debugging?

Question

I'm building an application that contains around 30 Forms. I need to manage sessions, so I would like to have a global LoggedInUser variable accessible from all forms. I read "David Heffernan"'s post about global variables, and how to avoid them but I thought it would be easier to have a global User variable rather than 30 forms having their own User variable. So I have a unit: GlobalVars ``` unit GlobalVars; interface uses User; // I defined my TUser class in a unit called User var LoggedInUser: TUser; implementation initialization LoggedInUser:= TUser.Create; finalization LoggedInUser.Free; end. ``` Then in my LoginForm's LoginBtnClick procedure I do : ``` unit FormLogin; interface uses [...],User; type TForm1 = class(TForm) [...] procedure LoginBtnClick(Sender: TObject); private { Déclarations privées } public end; var Form1: TForm1; AureliusConnection : IDBConnection; implementation {$R *.fmx} uses [...]GlobalVars; procedure TForm1.LoginBtnClick(Sender: TObject); var Manager : TOb…

Accepted Answer

"I assign this data to my global user" - what does this mean?

Through my crystal ball I see code similar to this in your Login form:

```
var
  user: TUser;
begin
  user := TUser.Create;
  try
    // assign properties/fields of user instance

LoggedInUser := user;
  finally
    user.Free;
  end;
end;
```

after that, `LoggedInUser` points at deallocated (and possibly reused) block of memory. Addressing any property/field of `LoggedInUser` will likely result in access violation.

Ha, quite close:

```
LoggedInUser:=u;
```

Add a method `Assign(aSource: TUser)` to your `TUser` class, which does a deep copy of values for all fields/properties (not reference assignments) and call it instead:

```
LoggedInUser.Assign(u);
```

Why is my global variable "inaccessible" when debugging?

Solution

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