duplicate inserts

[Bob Schellink <sa...@gmail.com>]

Currently, Click throws an exception if the same control is added multiple times to a Page or 
Container. This ensures we don't accidentally have two controls with the same name, but it adds 
usage problems for stateful Pages where we *do* want to replace existing controls and models. To 
work with stateful pages we often end up with the following code:

private Field field;

   public void onInit() {
     if (!form.contains(field)) {
       form.add(field);
     }
   }

or if you don't keep a reference to a control:

   public void onInit() {
     Field field = new Field();
     if (!form.getControlMap().containsKey(field.getName())) {
       container.add(field);
     }
   }


My feeling is that naming collisions within the same page/container is rather rare. So I propose we 
change current behavior to replace the existing object instead of throwing an exception. If there is 
a replacement we could log a message (in dev modes) that control x was replaced in container y, 
providing some indication that a replacement took place.

regards

bob

Re: duplicate inserts

[AndreyRybin <ap...@gmail.com>]

Very good idea.

My 5c:

- For stateless pages click can log WARNing in all modes except production
(for stateless pages - duplicate looks like real mistake). 
For stateful pages - info (or warn) in debug/trace mode.

- Javadoc should have explanation how prevent replacement (your examples
earlier)
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