Create Data Binding Programmatically

Overview

Under MVC approach, getting component's attribute value by calling getter methods causes lots of routine code in a composer. But under MVVM approach, all attributes' values are saved to ViewModel's properties automatically without calling any methods because of data binding. Through using a binder to add data binding for components, we also can enjoy this benefit in a composer. This section introduces basic usages of a binder.

Binder API Usage

There are 3 basic steps to create data bindings:

1. Initialize the binder
2. Store data objects as attributes

   To make data be available for EL expressions

3. Add data bindings

Assume we have a form to fill in personal information.

	<window apply="org.zkoss.reference.developer.mvvm.advance.DynamicBindingComposer" width="600px">
		<grid >
			<rows>
				<row>
					First Name:
					<textbox id="fn"/>
				</row>
				<row>
					Last Name:
					<textbox id="ln"/>
				</row>
				<row>
					Age:
					<intbox/>
				</row>
				<row spans="2">
					<div>
						<button label="Submit" />
						<button label="Reset" />
					</div>
				</row>
				<row spans="2">
					<div>
					Preview: I am <label id="fnLabel" /> <label id="lnLabel" />, <label id="ageLabel"/> years old.
					</div>
				</row>
			</rows>
		</grid>
		...
	</window>

We hope that user input can be automatically saved to a bean.

3 basic steps example

public class DynamicBindingComposer extends SelectorComposer {

	private Binder binder = new DefaultBinder();
	...
	private Person person;

	@Override
	public void doAfterCompose(Component comp) throws Exception {
		super.doAfterCompose(comp);
		
		binder.init(comp,this, null);
		
		grid.setAttribute("person", person);
		
		binder.addPropertySaveBindings(firstNameBox, "value", "person.firstName"
				, null, null, null, null, null,null,null);
		binder.addPropertyLoadBindings(firstNameBox, "value", "person.firstName"
				, null, null, null, null, null);
		// add more data bindings...
		
		binder.loadComponent(grid, false); //load beans' data to initialize components
	}

• Line 3: Create a DefaultBinder to use as its Javadoc suggests.
• Line 11: We should initialize DefaultBinder before using it. The first parameter is root component. The second parameter is ViewModel object. In this example, the composer plays the role as a ViewModel.
• Line 13: Set the data bean as an attribute of the Grid, this can make the bean be accessible for EL expression by its key: person.
• Line 15,17: Add save- or load-binding according to our requirement.
• Line 21: Load data for all load-binding inside the component specified at first parameter which is a Grid.

Here we give some common examples, for more details please refer to Javadoc: Binder.

Property binding in a ZUL

<textbox value="@bind(vm.person.firstName)"/>

Programmatic property binding

binder.addPropertyLoadBindings(firstNameBox, "value", "vm.person.firstName", null, null, null, null, null);
binder.addPropertySaveBindings(firstNameBox,"value","vm.person.firstName", null, null, null, null, null,null,null);

Add Data Binding for Collections

Assume that we hope end users can edit an item directly in a Listbox. Hence we could put a Textbox in each Listcell and make the Textbox bind to a object of Listbox's model. This data binding cannot be made by writing annotation in a zul because those Textboxs are dynamically created.

	<window apply="org.zkoss.reference.developer.mvvm.advance.DynamicCollectionBindingComposer"
		width="600px">
		...
		<div apply="org.zkoss.bind.BindComposer"
			viewModel="@id('vm') @init('org.zkoss.reference.developer.mvvm.advance.DynamicCollectionBindingVM')">
			<listbox model="@load(vm.personList)" selectedItem="@bind(vm.selectedPerson)" rows="10">

			</listbox>
			...
		</div>
		...
	</window>

Use ItemRenderer

	class MyListboxRenderer implements ListitemRenderer{

		public void render(Listitem listitem, Object data, int index)
				throws Exception {

			//TODO explain why
			listitem.setAttribute("each", data);
			
			//first name
			Listcell fnCell = new Listcell();
			listitem.appendChild(fnCell);
			Textbox fnBox = new Textbox();
			fnBox.setInplace(true);
			fnCell.appendChild(fnBox);
			binder.addPropertyLoadBindings(fnBox, "value", "each.firstName", null, null, null, null, null);
			binder.addPropertySaveBindings(fnBox, "value", "each.firstName", null, null, null, null, null, null, null);

			//last name
			...

			//age
			...

			//delete button
			...
		}
		
	}