It would be a fair assumption though
(a) to use TCollectionItem practicably you will be creating a derivative
class
(b) it is designed more for use with visual components that have a component
editor at design time and is used in conjunction with various types of
visual components.
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
> Behalf Of Dennis Chuah
> Sent: Monday, 9 July 2001 10:56
> To: Multiple recipients of list delphi
> Subject: RE: Listbox items (Was: Re: [DUG]: array of TStringList)
>
>
>
> > To get around this little problem when you need to keep lists of objects
> > created dynamically, Delphi provides the TList class. You can use
> > a TList or
> > make a derivative from it. It would be usual to override the
> destructor to
> > ensure all the memory is freed in your objects.
>
> In that case, I would strongly suggest you use TCollection instead as it
> maintains its items and will free them when deleted.
>
> Regards,
> Dennis.
>
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> > Sent: Saturday, 7 July 2001 00:32
> > To: Multiple recipients of list delphi
> > Subject: RE: Listbox items (Was: Re: [DUG]: array of TStringList)
> >
> >
> > Some understanding here is useful.
> >
> > It is not possible to create numerous objects with the same name.
> >
> > When you create an instance of a class (an object) you are doing several
> > things:
> > 1. Delphi reserves some memory for you
> > 2. Delphi gives you in the variable on the left hand side, a
> reference to
> > that piece of memory.
> >
> > If you then create another instance of the object using the
> same variable
> > name, you have lost access to the bit that you had before. it is
> > still there
> > but you have no way of accessing it, because the variable now
> > points to the
> > new bit you got. You can do this ten times but at the end you will still
> > only be able to access the last bit.
> >
> > To get around this little problem when you need to keep lists of objects
> > created dynamically, Delphi provides the TList class. You can use
> > a TList or
> > make a derivative from it. It would be usual to override the
> destructor to
> > ensure all the memory is freed in your objects.
> >
> > Now, when using a TList the above steps become:
> >
> > 1. Delphi reserves some memory for you
> > 2. Delphi gives you in the variable on the left hand side, a
> reference to
> > that piece of memory.
> > 3. You add the value of that variable to a TList object.
> >
> > Then you can use the methods of TList to access all those
> dynamic objects
> > you have created. In the days before OO we used to use linked lists of
> > pointers to do the same thing. Compared to that a TList is a doddle.
> >
> > Addressing to your particular situation. A record is not an object. A
> > Tobject is an object.
> >
> > I used to use records until I discovered how to use TList to
> link a whole
> > lot of dynamically created objects. To give an example I have
> just updated
> > an application that uses counters to count numbers in a big
> report, and do
> > various calculations etc. It used to use various TStringLists
> to store all
> > the counters. I updated it to use OO stuff. This is good
> because there are
> > two different types of counter and one is a subclass of the other.
> >
> > All you have to do is:
> > * Create an instance of your object e.g. MyObject := TMyObject.Create
> > * Do something with it...set the fields or something
> > * Add it to the Objects property of the list box items (which
> is probably
> > implemented as a TList) . No typecast needed since everything
> is descended
> > from TObject.
> >
> > Now you can safely reuse MyObject to create another instance, as the
> > reference is now saved in the list box. (Don't free it though,
> as it still
> > points to an instance, but if you wish you can set it to nil without
> > affecting any instances of your object)
> >
> > When you have to do something with your object, it looks like this:
> >
> > MyObject := TMyObject(ListBox1.Items.Objects[X]
> >
> > You have to typecast it because Delphi stores it as a TObject and
> > won't let
> > you access any of the methods or properties other than for a
> > TObject, if you
> > don't do the typecast, also you will get an "invalid type"
> error from the
> > compiler.
> >
> > Note that the Objects property still contains the reference until
> > that list
> > item is deleted.The question I am not at all sure about is
> whether Delphi
> > frees the memory associated with each object reference when the
> > list item is
> > removed from the list.
> >
> >
> > > -----Original Message-----
> > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
> > > Behalf Of Ross Levis
> > > Sent: Friday, 6 July 2001 23:33
> > > To: Multiple recipients of list delphi
> > > Subject: Re: Listbox items (Was: Re: [DUG]: array of TStringList)
> > >
> > >
> > > Thanks James, Ben & Reg. It's looks rather messy to me. I
> > > didn't realise you
> > > can create numerous duplicate objects with the same name. Is
> there any
> > > advantage to using a Record object as opposed to a class(TObject)?
> > >
> > > Ross.
> > >
> > > James Low wrote:
> > >
> > > > Thanks Ben ...
> > > >
> > > > -----Original Message-----
> > > > From: Ben Taylor [mailto:[EMAIL PROTECTED]]
> > > > Sent: 6 July 2001 17:01
> > > > To: Multiple recipients of list delphi
> > > > Subject: RE: Listbox items (Was: Re: [DUG]: array of TStringList)
> > > >
> > > > > AddObject('Somestring to display', myObject);
> > > > > myObject.Free; //the list owns a reference to it now
> > > >
> > > > you _really_ dont want to do this.. the list now has a
> pointer to the
> > > > object, but its still the same object. if you do the free, then the
> > > > list holds an invalid pointer.
> > > >
> > > > > myObject := Listbox1.Objects[ListBox1.Listindex];
> > > > this wont compile. you'll need to cast the TObject pointer to the
> > > > correct type:
> > > >
> > > > myObject := tRossesObject(Listbox1.Objects[ListBox1.Listindex]);
> > > >
> > > > that should work better..
> > > >
> > > > there are 'nicer' OO ways to do this but it's friday and
> i'm going now
> > > > :-)
> > > >
> > > > __________________________________________________
> > > > Do You Yahoo!?
> > > > Get personalized email addresses from Yahoo! Mail
> > > > http://personal.mail.yahoo.com/
> > > >
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