Solved

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

Posted on 2003-11-11
6
233 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
  • 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

PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

Question has a verified solution.

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

Suggested Solutions

The uses clause is one of those things that just tends to grow and grow. Most of the time this is in the main form, as it's from this form that all others are called. If you have a big application (including many forms), the uses clause in the in…
Introduction The parallel port is a very commonly known port, it was widely used to connect a printer to the PC, if you look at the back of your computer, for those who don't have newer computers, there will be a port with 25 pins and a small print…
This video shows how to quickly and easily add an email signature for all users on Exchange 2016. The resulting signature is applied on a server level by Exchange Online. The email signature template has been downloaded from: www.mail-signatures…
Email security requires an ever evolving service that stays up to date with counter-evolving threats. The Email Laundry perform Research and Development to ensure their email security service evolves faster than cyber criminals. We apply our Threat…

773 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