Solved

What causes "A component <> already exists" error?

Posted on 2003-11-11
6
235 Views
Last Modified: 2012-05-04
What causes "A component <> already exists" error?

MainFrm;

procedure TMainFrm.CallForm1Execute(Sender: TObject);
begin
  if not Assigned(Form1) then
     Form1:=TForm1.Create(application);
  Form1.Show;
end;

---------------------------------------------------------------------------------------

Form1;

procedure TForm1.FormClose(Sender: TObject;
  var Action: TCloseAction);
begin
  Action:=cafree;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  Form1:=nil;
end;

Usually this works but there are times that the error ("A component Form1 already exists" ) pops out ...


Thanks!
0
Comment
Question by:ttanyag
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
6 Comments
 
LVL 17

Accepted Solution

by:
geobul earned 100 total points
ID: 9729801
Hi,

I can't reproduce that error here. I have tried another way which worked well for me:

1.The calling part is the same (in your MainFrm).

2. In Form1

procedure TForm1.FormClose(Sender: TObject;
  var Action: TCloseAction);
begin
  self.Release;
end;

and without Destroy event.

Regards, Geo
0
 
LVL 17

Expert Comment

by:geobul
ID: 9729852
Oops, copied it in a wrong way. Sorry. Should be:

procedure TForm1.FormClose(Sender: TObject;
  var Action: TCloseAction);
begin
  self.Release; // or Form1.Release;
  FreeAndNil(Form1);
end;

Regards, Geo
0
 
LVL 12

Assisted Solution

by:andrewjb
andrewjb earned 100 total points
ID: 9730401
I've had this when:

a) I'm inheriting one form from another
and
b) I've got two .dfm files called the same, and the compiler is getting confused and picking up the wrong one.

So, make sure for your form, that the xxx.dfm file only exists in one place, and that you haven't got two units with the same name somehow.


Andrew.
0
 
LVL 27

Assisted Solution

by:kretzschmar
kretzschmar earned 100 total points
ID: 9732858
just to say,
that it is bad practice to use a reference-var
in its own methods

action := caFree; //is ok -> calls internal Release

>the error ("A component Form1 already exists" )
that you get this may caused by a too short create-call after the release,
because release sends a message to itself, and it could be,
that this message is not arrived, when you try to create the form new

i myself prefere to lookup the screen.forms-list for evaluating,
if a form is already there, rather than a test of nil to the reference-var

meikl ;-)
0

Featured Post

Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Objective: - This article will help user in how to convert their numeric value become words. How to use 1. You can copy this code in your Unit as function 2. than you can perform your function by type this code The Code   (CODE) The Im…
Creating an auto free TStringList The TStringList is a basic and frequently used object in Delphi. On many occasions, you may want to create a temporary list, process some items in the list and be done with the list. In such cases, you have to…
In an interesting question (https://www.experts-exchange.com/questions/29008360/) here at Experts Exchange, a member asked how to split a single image into multiple images. The primary usage for this is to place many photographs on a flatbed scanner…

726 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question