[udig-devel] Re: fun on trunk: socket plugin does what? and draw2drender

[Jody Garnett <jgarnett@xxxxxxxxxxxxxxx>]

Okay Jesse your arguments about listeners and so on are making Handlers 
not look like the best option (looks to be very tied into user interface 
concerns). While I feel I am going to have to force Commands into 
everyone's life sooner in the development learning curve rather than 
later it feels like commands and/or handlers do not fit the bill.

One final idea/warning - what you are setting up here has the danger of 
growing. I am wishing for a nice separation between blocks of 
functionality that we could start to script / and or invoke remotely / 
invoke from a ui. The JGrass project seems to have a separation between 
there console and their user interface already. I suspect it is done in 
a similar manner to what you are setting up now.

Jody

Jesse Eichar wrote:
> I also thought about using the handler.  It is not bad but it has no 
> "can handle" method.  So you basically have to try it and check if it 
> handled the message... I guess that is ok.  I can move the iteration 
> through all handlers into the SafeRunnable and keep trying until I get 
> one.
>
> The problem now is that IHandlers have state (listeners at minimum) 
> and some subclasses actually make it explicit and therefore is not 
> good for multi-threaded programming.  We would be tempting 
> implementers to create stateful Handlers which is a terrible idea for 
> this application.  Also as a parameter you get a ExecutionEvent as the 
> parameter which has a Map as the parameters so the developer cannot 
> use code completion easily to see what the parameter will be.
>
> None of these issues kill the idea it just is not a nice API to learn.
>
> Addressing the point we are making developers learn 2 APIs.  That is 
> absolutely true...  However the counter argument to that is that they 
> may not need to learn commands for a long long time.  I still haven't 
> for example and commands have been around as long as I have (4 years 
> now).  So having to learn commands is not a forgone conclusion.
>
> Jesse