FXMLLoader templates

[Martin Sladecek]

Hi,
I would like to discuss a 8.0 feature of FXMLLoader - the template flag.
I was introduced with this issue: 
https://javafx-jira.kenai.com/browse/RT-23413, but unfortunately, it 
never worked: https://javafx-jira.kenai.com/browse/RT-28121. I was 
trying to fix the issue, but the whole concept of a flag for loading 
templates seems hardly usable and incorrect to me and should be replaced 
with something more appropriate.

The reason is the handling of root, controller and the namespace before 
and after the load. Both are treated in 2 different ways. Before the 
load, they are used to adjust the following load - by setting the root 
(for <fx:root> tag), setting the namespace and a controller.
However, after the load, these properties (though not FX-properties) can 
be used to query what was just loaded. The root of the FXML, the 
namespace with all "id"s and the controller.

Now that's not very useful when you want to use template loading. My 
solution for RT-28121 (when keeping the old API) is to save the 
namespace after setTemplate(true) was called, using this namespace on 
each load(), clearing it at the begging of load() +  disallow 
setController() for this mode.

But that doesn't cover all of the relevant use-cases I can think of. 
Actually, without changing the API, I doubt we can support all such 
use-cases.

Here's the set I'm working with:
1) setup some "template namespace", n times do { adjust namespace (based 
on template namespace) , load) }

2) n times do {load, query id from namespace}

3) n times do {setController(new Controller) load }

4) n times do {load, query newly created controller}

5,6) same as 3,4 but with root

So while in 1,3 we would need to clear namespace/controller after each 
load, in 2,4 we need to clear it before each load. In case 3), 
forgetting to set a new controller would otherwise result in 2 instances 
with the same controller.

One solution might be to split this to 2 independent calls. 
setController/getLoadedController, ObservableMap getNamespace() and Map 
getLoadedNamespace (unmodifiable).

Another might be a completely new class FXMLTemplate.
It might yield new pre-set FXMLLoaders that can be adjusted and loaded, 
but it means generating a temporary object for each call.
Also, FXMLLoader would need to be updated, so that it's only possible to 
call load() once.

Other ideas / use-cases?

Thanks,
-Martin