[fpc-pascal] How to get a data module to notify of events?

[Frank Church]

On 15 September 2011 15:48, Martin Schreiber <mse00000 at gmail.com> wrote:

> On Thursday 15 September 2011 16:28:29 Frank Church wrote:
> > I have a form with some threaded objects that notify another form of
> events
> > by calling one of that forms events.
> >
> > I want to convert to a data module and any interested object to register
> > for those notifications.
> >
> > My idea is for each thread to have some kind of list of procedure types
> and
> > each interested object registers its routine eg.
> >
> > This is the data module. It is a rough sketch and may have some syntax
> > errors
> >
> > Type TOneArg = Procedure (Var X : integer);
> >
> > > type
> > >
> > >   TMonitorObject = class(TThread)
> > >   private
> > >
> > >     InterestedObjects: TList
> > >     procedure DispatchOutput;
> > >     procedure DisplayRawOutput;
> > >
> > >   protected
> > >
> > >     procedure Execute; override;
> > >
> > >   public
> > >
> > >     constructor Create(CreateSuspended: Boolean);
> > >     RegisterInterest(interestedProc:TOneArg);
> > >
> > >   end;
> > >
> > > TMonitorObject.RegisterInterest(TOneArg);
> > > begin
> > >
> > >    InterestedObjects.Add(interestedProc);
> > >
> > > end;
> > >
> > > procedure TMonitorObject.DispatchOutput;
> > > begin
> > >
> > >    foreach InterestedObject do
> > >
> > >     InterestedObject.Procedure.Execute;
> > >
> > > end;
> > >
> > > constructor TMonitorObject.Create(CreateSuspended: Boolean);
> > > begin
> > >
> > >   inherited Create(CreateSuspended);
> > >   InterestedObjects := TList.Create
> > >   FCycleComplete := True;
> > >
> > > end;
> >
> > Do the procedures for the objects which require notification need to be
> > constructed in some way?
> >
> MSEgui has such a notification mechanism with automatic unlinking by
> destroying the objects, see tobjectlinker in
> lib/common/kernel/mseclasses.pas.
> Another possibility is to use a tobjectevent descendant and
> application.postevent.
>
> > Am I on the right track here? I am particularly interested in what
> happens
> > when the objects passing the routines are destroyed without the data
> module
> > knowing about it.
>
> The program most likely will crash. :-)
>
>

I want to know if my approach is a workable one and what the right syntax
should be, handling the destroyed objects I believe I can deal with by
checking for the existence of the object before notifying it.
Are there some examples of that somewhere?


> Martin
> _______________________________________________
> fpc-pascal maillist  -  fpc-pascal at lists.freepascal.org
> http://lists.freepascal.org/mailman/listinfo/fpc-pascal
>



-- 
Frank Church

=======================
http://devblog.brahmancreations.com
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