<div apply="org.zkoss.bind.BindComposer"
	viewModel="@id('vm') @init('org.zkoss.support.imperatives.FormBeanValidatorVM')"
	validationMessages="@id('vmsgs')"
	form="@id('fx') @load(vm.bean) @save(vm.bean, before='save') @validator(vm.beanValidator, prefix='p_')">
	<combobox id="cbx" model="@load(vm.letters)" selectedItem="@bind(fx.letter)"
		errorMessage="@load(vmsgs['p_letter'])"
		onChange="@command('onChangeLetter')">
		<template name="model">
			<comboitem label="${each}" />
		</template>
	</combobox>
	<button onClick="@command('save')">Save</button>
</div>

public class FormBeanValidatorVM {
	ListModelList<String> letters = new ListModelList<String>();
	Bean bean = new Bean();
	Validator validator;

	@Init
	public void init() {
		letters.addAll(Arrays.asList(new String[] { "a", "b", "c", "d", "e", "f", "g" }));
	}
	
	@Command
	public void onChangeLetter() {
		letters.add("h");
	}
	
	@Command
	public void save() {
	}
	
	public ListModelList<String> getLetters() {
		return letters;
	}
	
	public Bean getBean() {
		return bean;
	}
	
	public Validator getBeanValidator() {
		if (validator == null) {
			//validator = new CascadingFormBeanValidatorService();
			validator = new Validator() {
				public void validate(ValidationContext ctx) {
					String value = (String) ctx.getProperties("letter")[0].getValue();
					System.out.println("Validate value: " + value);
				}
			};
		}
		return validator;
	}

	public class Bean {

		@NotBlank
		private String letter;

		public String getLetter() {
			return letter;
		}

		public void setLetter(String letter) {
			this.letter = letter;
		}

	}
}