Decoration, Validation and UI issues

[errael]

This discussion is related to PR #186. 2014/01/22. It describes specifics about
the PR, things that led to the PR, and issues discovered while putting together
the PR. It is not fleshed out and undoubtedly incomplete. There may be follow on
comments and hopefully the community with offer insight.

SSCommon

• There's final flag DISABLE_GENERAL_VALIDATION; when set, only
  SSFormattedTextField gets a decorator.
• At end of the file, read comments about decoration/validation.

New stuff

• Interface Validator
  App can set this for additional checks
• SSComponentInterface.isDataValid() - default true
  Indication of compenent valid, maybe only meaningful for SSFormattedTextField
• Interface Decorator - draws visual indicator
  Typically does Validator.validate() && SSComponent.isDataValid()
• SSCommon handles Decorator and Validator

Validation points where data can be checked for validity

1. Component builtin validation (SSFormattedTextField)
2. Per component checks with validation mechanism
3. When database written possible SQL exception
4. Group validation for multiple interacting components

UI/App choices

• SQL exception handling
  • dialog (widely used in SwingSet (only way exception handled?))
  • error state
  • message attached to component
• Focus change strategy in the face of errors
  • Lock to component (SSFormattedTextField is like this (more or less)).
  • Don't lock Mark any component with error.
  • This should probably be an App UI decision and consistent.
• Decorator look&feel

When component change
Never gets here if SSFormattedTextField violation.
If validation check return then try to write to database

Other

• If decorator/validator used on ordinary JTextField, and there's an error,
  hitting next keeps the error focus on the next record. This may simply be
  a bug; it might be a flaw somewhere.

There's PR #187, built on #186. It shows a 3rd party decoration/validation
infrastructure, SimpleValidation https://github.com/timboudreau/simplevalidation,
used with SwingSet; the swingset-demo/.../simpval directory has the beginnings
of utilities and helpers for using SimpleValidation.

Using this, each SSTextField can have it's own error message as a badge tool tip.
I can imagine that an SQL exception message is captured and associated with the
SSComponent.