How to stop workflow from transitioning to next state

[Karanam Subbarao]

How do I stop workflow transition using the validator based on the value in Custom Field.  I was able to develop a Post function which will not change the status. But I was not able to stop the transition. 

I know I can hide the workflow transition Button using a Condition statement.  But it doesnt suite my requirement.

Any advice

[Nic Brough -Adaptavist-]

Use a validator.  Conditions block access to the transition, post-functions are for doing updates after a transition is definitely valid.  Validators are for checking input during a transition.  A validator will check data and return either "true" for "yes, valid information" or "false" for "nope, don't let it happen", with an optional message in the validation.