Hello.
1. I have a piece of code that is killing me:
I want to create a MDI application.
I have a main form that automatically creates a new child form called
'Project Manager'. It can't be close, only minimized. It is
automatically destroyed by the application when it terminates.
I use this 'Project manager' to create other (one or more) child forms
called Grids. I should be able to close those forms (caFree) at any time
or I can leave them open and close the application to close them for me
when it finish. The question is: why I can't pass *nil *as parameter
when I create these forms?
procedure TFormManager.Start;
begin
with TFormGrid.Create(*nil*) DO <<< if I
pass _Application_ or _Self_, it works!
begin
...some code here;
end;
end;
procedure TFormGrid.FormClose(Sender: TObject; var Action: TCloseAction);
begin
Action:= caFree;
end;
I think until here everything is right. Right?
When I close the whole application and one or more of these Grid forms
are open, it crashes in this procedure:
procedure TMainForm.FormResize(Sender: TObject); { <- this is
supposed to keep the child forms at the same width with the main form
when the user resize the interface }
VAR i: Integer;
begin
for I:= MDIChildCount-1 DownTo 0 DO
begin
if (MDIChildren[i] is TFrmGrid) then
if (MDIChildren[i] as TFrmGrid).HandleAllocated
then
begin
if ((MDIChildren[i] as TFrmGrid).WindowState= wsNormal)
<<<< *CRASH HERE*. Exception class C0000005 with message 'access
violation at 0x0055bc6b: read of address 0x00000000'.
then
begin
(MDIChildren[i] as TFrmGrid).Left:= 0;
(MDIChildren[i] as TFrmGrid).Width:= MainForm.ClientWidth-4;
end;
end;
end;
end;
I suppose is something with those 'dangling' pointers, so my next
question is:
2. Why Delphi does only a 'Free' on a object/form when it automatically
destroy it instead a FreeAndNil?
The application works very well with Self or Application instead of Nil
but the documentation says that Application is not recommended because
it is slow and Self should be used OLNY when the Create belongs to the
main form (and in my case I don't create those Grids in the main form).
So the only answer is NIL.
Why does not work?
Thanks.
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