Java Swing dependent field validation

Question

During a focus transfer, is there a way to validate dependent fields such that a focus transfer among JComponents (a, b, c) is not vetoed but a focus transfer to some external element (say, d) is vetoed?

The most natural place to do such a thing seems to be in InputVerifier.shouldYieldFocus(); however, I don't see a way to obtain the (next) focus target at that time.

Answer 1

Not supported by the InputVerifier mechanism. And probably shouldn't at that level of granularity because it might lead to giving focus to d with invalid data in a.

Assume an InputVerifier which does know the opposite component (that is the potential next focusOwner) and its data is invalid

• in shouldYieldFocus it tests the opposite
  • for b it allows the transfer
• transferred focus to b
• transfer focus to d (allowed)

(same overall effect with Rob's suggestion, btw, except that the a's InputVerifier is never run)

On the whole, the built-in validation support isn't very strong - lots of work left for the developer. Some things you would need to do

• can use InputVerifiers on the per-component level to actually do the validation, shouldYield returns true always
• have some "InputVerifierController" which checks whether the focus is going "to the outside"
• if going "outside" with any invalid data anywhere "inside" prevent the transfer

Using a framework like f.i. JGoodies Validation might be easier.

Answer 2

For the dependent components you should be able to use:

component.setVerifyInputWhenFocusTarget( false );