Questions about dataengines and apologizes

[Matthieu Gallien]

2011/1/20 Aaron J. Seigo <aseigo at kde.org>

> On Thursday, January 20, 2011, Matthieu Gallien wrote:
> > I believe that some of the current solutions rely on encoding the address
> > in the name of a requested source.
>
> it often is, yes.
>
> > I am not sure if a service could be used and how.
>
> you could, yes, by implement serviceForSource and returning a Service
> object
> from there that is (internally) associated with that source. it could offer
> operations like "connect" with a string for the hostname and an optional
> int
> for the port. when called, that operation would then set some internal
> properties.
>
> the way i usual recommend doing this is by subclassing DataContainer to do
> all
> the network stuff and when serviceForSource is called, passing the
> DataContainer subclass object to the Service subclass :) keeps everything
> nicely separated and clear in the code.
>
> you could, of course, do the entire thing as a Service and not use a
> DataEngine at all. it probably quite depends on what sort of communication
> happens with the server; if it's a stateless "make a request, the server
> returns an answer" like http then a plan Service might be more
> straightforward. if there is ongoing communication with the server and/or
> the
> data ought to be shared between multiple widgets, then a DataEngine
> probably
> makes more sense.
>

In my case (train model and DCC control), the server (rocrail) is also
sending change notifications to connected clients, so the dataengine
approach makes sense. Even if I could use one source per server, I would
have preferred to split the informations into several sources to avoid
updating everything on any change. In this case, several sources would be
sharing one server connection. Is there already something for that in
libplasma or should I use some sort of smart pointer to share the object and
control its lifetime ?

At least, I will give a try to the smart pointer approach when time permits.

I plan to build an applet using QML plasma bindings. I believe that the
first approach with server address encoding in the source name will be more
practical. What do you think ?


> > PS : by the way, I noticed that there is no techbase tutorial on writing
> > services in a data engine. If the way it is done in the task engine is
> > correct, I can try in the following month to make some text, but I will
> > need a review from somebody.
>
> yes, the task engine is a reasonable example :)
>
> a simple example in kdeexamples/plasma/c++/dataengines/ would be nice, too,
> if
> you felt like it.
>

Ok, I will do. Do you if this module will move to git ?

>
> --
> Aaron J. Seigo
> humru othro a kohnu se
> GPG Fingerprint: 8B8B 2209 0C6F 7C47 B1EA  EE75 D6B7 2EB1 A7F1 DB43
>
> KDE core developer sponsored by Qt Development Frameworks
>
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> Best regards
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