Well who would have believed that FreeAndNil has a bug in it!
The following code shows the essence of the problem.
type
TA = Class
destructor Destroy;
end;
TB = Class
destructor Destroy;
procedure SomeMethod;
end;
var
A : TA;
B : TB;
destructor TB.Destroy;
begin
FreeAndNil(A);
inherited;
end;
procedure TB.SomeMethod;
begin
{ Some code that references other fields/methods in TB - The exception occurs
at this point };
end;
destructor TA.Destroy;
begin
B.SomeMethod; { If using FreeAndNil, then B is already nil at this point.
SomeMethod is still called, but with a self of 0 }
inherited;
end;
begin
A : TA.Create;
B : TB.Create;
FreeAndNil(B); <- This fails in TB.SomeMethod. Because B is set to nil
before it's freed.
B.Free; <- This works.
B := nil;
end;
If you check the VCL source code (in Delphi 7 at least) then it really does Nil
before it Frees.
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