validation - How to validate inputs and prevent save actions using databinding in eclipse? -

i want create input forms validate user input , prevent model being saved invalid data. have been using databinding works point implementation not intuitive like.

imagine input contains '123' , value must not empty. user deletes characters 1 one until empty. databinding validator shows error decoration.

however, if user saves form , reloads it, '1' displayed in field - i.e. last valid input. databinding not transmit invalid value model.

i have changelistener called before databinding @ point invalid state has not been detected.

i error displayed in ui model remains valid (this so). also, long ui contains errors, should not possible save model.

/**  * bind text control property in view model  **/ protected binding bindtext(databindingcontext ctx, control control,         object viewmodel, string property, ivalidator validator) {     iobservablevalue value = widgetproperties.text(swt.modify).observe(             control);     iobservablevalue modelvalue = beanproperties.value(             viewmodel.getclass(), property).observe(viewmodel);     binding binding = ctx.bindvalue(value, modelvalue, getstrategy(validator), null);     binding.gettarget().addchangelistener(listener);     controldecorationsupport.create(binding, swt.top | swt.left);      return binding; }  private updatevaluestrategy getstrategy(ivalidator validator) {     if (validator == null)         return null;      updatevaluestrategy strategy = new updatevaluestrategy();     strategy.setbeforesetvalidator(validator);     return strategy; }  private ichangelistener listener = new ichangelistener() {     @override     public void handlechange(changeevent event)     {     // notify form listeners has changed          } };  /**  * called form owner check if form contains valid data e.g. before saving  **/ public boolean isvalid() {     system.out.println("isvalid");     (object o : getdatacontext().getvalidationstatusproviders())     {         validationstatusprovider vsp = (validationstatusprovider) o;         istatus status = (istatus)vsp.getvalidationstatus()                 .getvalue();         if (status.matches(istatus.error))             return false;     }     return true; } 

your best bet steer clear of changelisteners - you've discovered, order of execution either undefined or not helpful in case.

instead, want stick 'observable' opposed 'listener' model long possible. mentioned, create aggregatevalidationstatus listen overall state of databindingcontext, has similar effect existing code.

then can either listen directly (as below) affect save ability, or bind bean.

iobservablevalue statusvalue = new aggregatevalidationstatus(dbc, aggregatevalidationstatus. max_severity);  statusvalue.addlistener(new ivaluechangelistener() {     handlevaluechange(valuechangeevent event) {         // change ability save here...     } });