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Create Open Dialog

Posted on 2007-11-16
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Last Modified: 2010-04-04
When I try to create a TOpenDialog I get an EAccessViolation Error. Here is my code where the error occurs:

var
  OpenDlg: TOpenDialog;
  filename: string;

procedure TForm1.FormCreate(Sender: TObject);
begin
  OpenDlg.Create(OpenDlg); //Access Violation
  if OpenDlg.Execute then
  begin
    filename := OpenDlg.FileName;
  end;

Could anyone tell me how to fix this?
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Question by:ding-dong
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8 Comments
 
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Accepted Solution

by:
MerijnB earned 125 total points
ID: 20300348
procedure TForm1.FormCreate(Sender: TObject);
begin
  OpenDlg := TOpenDialog.Create(OpenDlg); //Access Violation gone
  try
    if OpenDlg.Execute then
    begin
      filename := OpenDlg.FileName;
    end;
  finally
    OpenDlg.Free();
  end;
end;
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LVL 18

Expert Comment

by:Johnjces
ID: 20300369
Try this...

procedure TForm1.Button1Click(Sender: TObject);
begin
  OpenDlg := TOpenDialog.Create(self); //Access Violation
  if OpenDlg.Execute then
  begin
    Edit1.Text := OpenDlg.FileName;
  end;  
end;

John
0
 
LVL 18

Expert Comment

by:Johnjces
ID: 20300373
Woops... remove the comment //Access violation as it is not there.

John
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by:MerijnB
ID: 20300379
always refresh before you post a comment :)
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Expert Comment

by:Johnjces
ID: 20300411
MerijnB

WoopS! Alright I see the problem!!!! In just before me!

Sorry about that! I see that happen every so often... first time for me!

;-) John

0
 
LVL 26

Expert Comment

by:Russell Libby
ID: 20301264
The following code:

  OpenDlg:=TOpenDialog.Create(OpenDlg);

Is going to be prone to problems, and should not be used. If OpenDlg is not cleared (left pointing to an already freed object; aka stale pointer), then an access violation WILL occur. Not a problem for the first time use when the var is global in scope, but the second time is an issue. This is also an issue if the var is local in scope (not guaranteed to be nil). In short, poor practice.

If you don't need an owner then use var:=TOpenDialog.Create(nil), or as John pointed out, use Self, which in this case refers to the object who's method your calling (TForm1).

Russell


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LVL 19

Expert Comment

by:MerijnB
ID: 20301279
oops, sorry, that was a very big typo, should of course be: OpenDlg := TOpenDialog.Create(self);
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Expert Comment

by:MerijnB
ID: 20301280
(glad you are paying attention :))
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