Data and Collections

Expose ViewModel's Properties

ViewModel, like a JavaBean, exposes its properties through getter and setter methods. Any property that View (ZUL) wants to retrieve through data binding should have a corresponding getter method. The method's return type can be primitive type (int, boolean...), or a JavaBean. If a UI component needs to save its attribute value (it's usually user input) back to ViewModel's property, the ViewModel should provide a corresponding setter method. Therefore, through setter and getter can change the data of both the View and the ViewModel using the data binding mechanism.

Property is Primitive Type

Primitive type property

public class PrimitiveViewModel {

    private int index;
    private double price;

    public int getIndex() {
        return index;
    public void setIndex(int index) {
        this.index = index;

    public double getPrice() {
        return price;
    public void setPrice(double price) {
        this.price = price;


A zul that uses PrimitiveViewModel

<window apply="org.zkoss.bind.BindComposer" viewModel="@id('vm') @init('foo.PrimitiveViewModel')">

    <intbox value="@bind(vm.index)"/>

    <doublebox value="@bind(vm.price)"/>

    <!-- other components -->

  • @id('vm') sets ViewModel name, then we can use vm to reference ViewModel's property in the following components. (line 1)

Property is Object or JavaBean

If a property is a JavaBean, that JavaBean's property can also be accessed through an EL expression.

Object type property

public class Address {

    private String city;
    private String street;

    //gettter & setter

public class ObjectViewModel {

    private Integer index;
    private String name;
    private Address address;

    public int getIndex() {
        return index;
    public void setIndex(Integer index) {
        this.index = index;

    public String getName() {
        return name;
    public void setName(String name) { = name;

    public Item getAddress() {
        return address;
    public void setAddress(Address address) {
        this.address = address;


A zul that uses ObjectViewModel.

<intbox value="@bind(vm.index)"/>

<textbox value="@load("/>

<label value="@load(vm.address.street)"/>
  • vm.address is a JavaBean, and we can access its property street with EL expression vm.address.street. (line 5)

Property is Collection

If the UI component is a collection container like listbox or grid, it should be bound to a property whose type is Map or subinterface of Collection like List or Set.

Collection type property

public class CollectionViewModel {
    //primitive type
    private int selectedIndex;
    private List itemList;

    public int getSelectedIndex() {
        return selectedIndex;
    public void setSelectedIndex(int index) {
        selectedIndex = index;

    /* As we can't save whole list through data binding,
    the ViewModel only provides getter for itemList.*/
    public List getItemList() {
        return itemList;

A zul that uses CollectionViewModel

<label value="@load(vm.address.street)"/>
<listbox model="@load(vm.itemList)" selectedIndex="@bind(vm.selectedIndex)">
    <template name="model" var="item">
        <listitem label="@load("/>
  • Line 2: Listbox's model attribute should be bound to a collection object, vm.itemList.