[Laszlo-user] API Change Proposal: SetVisibility to replace SetVisible

[P T Withington]

Please comment on this proposed API change which we would like to  
implement for 4.1 (RingDing).

Problem:

SetVisible currently accepts null|false|true, where null has the  
special meaning 'let data control visibility'.  This is a poor  
interface because it is too easy to accidentally pass a value of  
null.  The `visible` attribute cannot be used to ask programmatically  
if a view is visible or not for the data-bound case.

Proposal:

1. Add a new attribute `visibility` that is a read/write String and  
has values  'visible', 'hidden', 'collapse'. This is implemented by a  
setter that  maps 'visible' -> true, 'hidden' -> false, 'collapse' ->  
null in the old  mechanism.

2. Deprecate `setVisible`:  issue a warning telling how to get the  
same effect with `setVisibility`.  Make `visible` reflect the actual  
state of the view (do not store the value passed to `setVisible`).

3. In the next major release make `setVisible` a no-op so that  
`visible` is read-only and reflects the actual state of the view  
(i.e., if `visibility` is 'collapse', it will be true when there is  
data and false otherwise).

Evaluation:

Pro:  1) Replaces an error-prone interface.  2) Solves the problem of  
programmatically query a view's visible state.  3) Uses an interface  
that is compatible with CSS.

Con:  1) Programs will have to be updated to use the new API.