[fpc-devel] TComponent.Name can not be set to ''

[Michael Van Canneyt]

On Wed, 20 Jun 2007, Marc Weustink wrote:

> Michael Van Canneyt wrote:
> > 
> > On Wed, 20 Jun 2007, Marc Weustink wrote:
> > 
> > > Michael Van Canneyt wrote:
> > > > On Wed, 20 Jun 2007, Marc Weustink wrote:
> > > >
> > > > > Michael Van Canneyt wrote:
> > > > > > On Wed, 20 Jun 2007, Micha Nelissen wrote:
> > > > > >
> > > > > > > Michael Van Canneyt wrote:
> > > > > > > > This is due to a Delphi compatibility fix. Component names must
> > > > > > > > be
> > > > > > > > valid
> > > > > > > > identifiers. Logical, since the name must match the field name
> > > > > > > > in
> > > > > > > > the
> > > > > > > > form,
> > > > > > > Why *must* it match a field name in the form ?
> > > > > > Because the streaming depends on it.
> > > > > >
> > > > > > The stream contains the component name. The streaming mechanism
> > > > > > creates
> > > > > > a
> > > > > > component, sets it's name and then matches this name with the list
> > > > > > of
> > > > > > published fields of TForm, and then fills in the pointer.
> > > > > And what if a published field isn't found ?
> > > > Nothing. Since there is no pointer to fill in, nothing happens.
> > > >
> > > > And this is right, because if you were to create everything run-time,
> > > > and
> > > > stream
> > > > that, there are no pointers to fill in when the stream is being read
> > > > again.
> > > :)
> > > then back to Michas question: why must ?
> > 
> > Because in the form declaration, the fieldname must match the name.
> > 
> > Given
> > 
> >   TMyForm = Class(TForm)
> >     MyButton : TButton;
> >   end;
> > 
> > and a form file
> > 
> > Object TmYForm
> >   Object MyButton : TButton
> >     Caption = 'Click here'
> >   end
> > end
> >     The MyButton (=component name) in the form file is used to look up the
> > MyButton field in TMyForm. If it doesn't find that, then things in code like
> > 
> > MyButton.Enabled:=False;
> > 
> > Would lead to a nice access violation, if the instance pointer is Nil...
> 
> Yes, I do understand this. An ide (or someone doing this manually) should
> handle this. And for components which are streamed this way its a requirement.
> However, it is IMO a bit strange that there are limitations on some property,
> only because some usage indirectly requires a valid identifier. IMO, the
> creator of this usage is responsible for that, not the component itself.

Maybe, but the current behaviour is Delphi compatible, and so it stays.

The streaming and thus TComponent was designed for form handling, so the 
implementation is entirely in function of the usage.

If you don't want this behaviour, you can start at TPersistent, which
can also be streamed, but does not have the restriction.

Michael.