Question

Let’s say I have two forms in a delphi project, I want to be able to access form1’s variables from form2. Is there anyone to declare, say a ‘public’ variable in form1 which can be read from all forms?

I have tried putting a variable in the public declaration

    { private declarations }
  public
    { public declarations }
  test: integer;
  end;     

and in form 2 i have

    unit Unit2;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, unit1;

type

  { TForm2 }

  TForm2 = class(TForm)
    procedure FormClose(Sender: TObject; var CloseAction: TCloseAction);
    procedure FormCreate(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end; 

var
  Form2: TForm2; 
implementation

{$R *.lfm}

{ TForm2 }

procedure TForm2.FormCreate(Sender: TObject);
begin
  form1 //<---------- DOES NOT GET RECOGNIZED
end;

end.

I then put ‘Unit1’ into the uses section on Form2, but it seems I can’t do that due to a circular reference. I’d like to refrain from using pointers if possible.

Answer 1

First, if you must use globals (it’s probably better not to use globals, as Craig has wisely pointed out) then you should put the globals you want to share in SharedGlobals.pas:

unit SharedGlobals;
interface
var
   {variables here}
   Something:Integer;
implementation
    { nothing here?}

Now use that unit, from the two units you want to share access to that variable in. Alternatively, have both reference another object, which is named something sensible, and have that object be designed, as the holder of state (variable values) that those two instances (forms or classes, or whatever) need to share.

Second idea, since your two units that you have already have dependencies on each other, you could also get around your circular dependency by using the unit that would create a circular dependency, from the implementation section instead of the interface:

 unit Unit2;
 interface
   /// stuff
 implementation
    uses Unit1; 

…

 unit Unit1;
 interface
   /// stuff
 implementation
    uses Unit2;