Delphi: Undeclared Identifier in Procedure

Question

I want to edit a property of a shape inside a procedure. However if I create my own procedure I get an "undefinded identifier" error.

I tried to edit the property in the OnCreate event procedure of my form and that works just fine.

Why is it like that and how can I fix it?

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls;

type
    Tfrm_main = class(TForm)            
    shp_wheelLeftInside: TShape;
    shp_wheelRightInside: TShape;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }

  public
    { Public declarations }
  end;

var
  frm_main: Tfrm_main;

implementation

{$R *.dfm}

procedure addWheelInsides();
begin

    shp_wheelRightInside.Height := 42;           //this is where the error occurs

end;

procedure Tfrm_main.FormCreate(Sender: TObject);
begin

   shp_wheelLeftInside.Height := 42;
   shp_wheelRightInside.Height := 42;

  addWheelInsides();

end;

end.

The form does not know anything about your procedure ...add it : var frm_main: Tfrm_main; procedure addWheelInsides; implementation Yes, and you can like Sami said add TShape to your procedure. — user763539

J... J... · Accepted Answer · 2017-01-31T16:53:26

The problem is that shp_wheelRightInside is a field that belongs to your Tfrm_main class whereas the addWheelInsides() method you have declared as a naked, ordinary method that belongs to nothing. The method, therefore, does not have access to the fields which belong to the form.

One solution is to move the method, which intends to operate on objects owned by the form, into the form itself.

  Tfrm_main = class(TForm)            
    shp_wheelLeftInside: TShape;
    shp_wheelRightInside: TShape;
    procedure FormCreate(Sender: TObject);
  private
    procedure addWheelInsides();  {declare it here}    
  public
    { Public declarations }
  end;

Which you then implement as a method of the form class as :

procedure Tfrm_main.addWheelInsides();
begin    
  shp_wheelRightInside.Height := 42;   
end;

Delphi: Undeclared Identifier in Procedure

2 Answers