Question

This is my code:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ComCtrls;

...

implementation

{$R *.dfm}

uses Unit2;

...    

procedure TForm1.Button4Click(Sender: TObject);
begin
  Frame2.Show;
end;

I got this compiler error:

Undeclared identifier: ‘Frame2’

Then I tried to declare it:

Frame2: TFrame2;

Edit:

Further explenation form comment.

Ok I will be precise. I use anwser ardnew Frame2: TFrame; and I get ** access violation** and with out it I get Undeclared identifier: ‘Frame2’ now I’m more precise?

Answer 1

You did not show the contents of Unit2, so we can only speculate. It sounds like there is no Frame2 global variable declared in Unit2.pas. That would account for the undeclared identifier error. Declare the variable yourself, and instantiate an instance of the TFrame2 class before you can then Show() it, eg:

unit Unit1; 

interface 

uses 
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, 
  Dialogs, StdCtrls, ComCtrls; 

... 

implementation 

{$R *.dfm} 

uses
  Unit2; 

var
  Frame2: TFrame2 = nil;

...     

procedure TForm1.Button4Click(Sender: TObject); 
begin 
  if not Assigned(Frame2) then
  begin
    Frame2 := TFrame2.Create(Self);
    Frame2.Parent := Self;
  end;
  Frame2.Show; 
end;