[Gambas-user] Problems with controls - text property

[Steven Lobbezoo]

OK Benoit, I changed it from control to object.
It's right that it's a bit slower, but user wont notice, so all is ok now.

Towards your explanation in english of Static typing and Virtual Classes :
I think your english is perfect, but my japanese is awfull ;-)

I might have to learn something about OO in the end :-(

Steven


Le vendredi 27 avril 2007 00:52, Benoit Minisini a écrit :
> On vendredi 27 avril 2007, ron wrote:
> > On Thursday 26 April 2007 23:05, Steven Lobbezoo wrote:
> > > Hi,
> > >
> > > I dont get it, if I do the following :
> > > -----------------------------------------------------------------------
> > >-- ---- FOR EACH ctrl IN ME.Controls
> > >         IF ctrl.Name = tmp THEN
> > >           IF ctrl.Tag <> ctrl.Text THEN
> > >             ' ok, we've changed something, let's write it back
> > >             IF SqlPrt THEN SqlPrt = SqlPrt & ","
> > >             SqlPrt = SqlPrt & " " & Object.GetProperty(ctrl, "Name") &
> > > " = '" & Object.GetProperty(ctrl, "Text") & "' "
> > >           END IF
> > >           BREAK
> > >         END IF
> > >       NEXT
> > > -----------------------------------------------------------------------
> > >-- ----
> > >
> > > I get  "Unknown symbol 'test' in class control"
> > >
> > > Certanly there are  controls in the form that not have a property
> > > 'text', but I filter them out with the line "        IF ctrl.Name = tmp
> > > THEN   " Since ALL the controls that satisfy this condition have a
> > > property "text".
> > >
> > > If I look into the vars ctrl.Tag and ctrl.Text there is a value, no
> > > problem there.
> > >
> > > So, why do I get this error ?
> > >
> > > Steven
> >
> > Because the controls does not have a name property.
> >
> > What you see "as" name is in the design mode.
> >
> > This 'name' thing does have a long history of wishes but Benoit
> > decided not to implement and suggest to use the 'Tag' property for
> > storing your name of the control.
> >
> >
> > BTW
> > SqlPrt = SqlPrt & " " & Object.GetProperty(ctrl, "Name") & " = '" &
> > Object.GetProperty(ctrl, "Text") & "' " can be
> > SqlPrt = SqlPrt & " " & ctrl.Name & " = '" & ctrl.Text & "' "
> >
> > if the .name was implemented.
> >
> > The other way is using the useless ID property.
> >
> > DIM YourTmp as Control
> > ' you need next line to get the ID of created control in a fixed way
> > YourTmp = new TextBox(Form) as "Tmp"
> >
> > and use in your Sub
> >
> >        FOR EACH ctrl IN ME.Controls
> >          IF ctrl.ID = YourTmp.ID THEN
> >            IF ctrl.Tag <> ctrl.Text THEN
> >
> > You can also in design mode fill the 'Tag' with the name of the
> > control and in the Form.Open or .new read the 'Tag', store it in
> > collection and clear the content of 'Tag'
> >
> > the collection key is the content of the 'Tag' and the value the .ID of
> > the control
> >
> >        FOR EACH ctrl IN ME.Controls
> >          IF ctrl.ID = YourIdCollection['tmp'] THEN
> >            IF ctrl.Tag <> ctrl.Text THEN
> >
> > 		SqlPrt = SqlPrt & " " & YourIdCollection.key & " = '" & ctrl.Text & "'
> > " or
> > 		SqlPrt = SqlPrt & " " & "tmp = '" & ctrl.Text & "' "
> >
> >
> >
> > Ron
>
> Hmm... It is absolutely not that :-)
>
> The Name property has been implemented for a while.
>
> The problem is that Steven didn't understand that if *he* knows that his
> test is true only for control having the Text property, Gambas does not.
>
> Gambas uses static typing with virtual dispatching.
>
> 'Static typing' means that the class of an object is given by the
> declaration of the variable that contains its reference.
>
> 'Virtual dispatching' means that the symbol (method or property) applied to
> this reference will call the implementation of the true object class, not
> the class given by the declaration of the variable.
>
> So if the 'ctrl' variable is declared 'AS Control', then you can only use
> symbols of the Control class on it.
>
> If you want Gambas to use dynamic typing, i.e. detects that the Text
> property exists each time it uses it, then you must declare the 'ctrl'
> variable 'AS Object'. But this is slower, as each symbol applied to 'ctrl'
> will need a lookup in the symbol table of the object class.
>
> I hope I was clear, as it is difficult for me to explain that in English.
>
> Note that is exactly like C++, with classes having virtual methods only.
> Except that C++ has no dynamic typing of course.
>
> Regards,