Monday, June 11, 2012

ZK in Action [2] : MVVM - Update View Programmatically

In the previous 2 posts we've used ZK's MVVM functionalities to:

We've seen when a method is decorated with the annotation @NotifyChange(), upon its execution completes, the Binder would be informed of the VM property's changes so that Binder can update the corresponding UI accordingly. 

In this post, whilst we implement the functionality of item deletion in our inventory, we'll see how we can update UI components programmatically at runtime.


Build a delete function to our simple inventory CRUD feature.

Select Item in Table, Click "Delete", Confirm Deletion

ZK Feature in Action

  • MVVM : BindUtils

Implement Deletion with MVVM BindUtils

We will:
  • Add markup for the delete button and assign it an onClick event handler
  • Implement command method "deleteItem()" in VM

The Markup
<window apply="org.zkoss.bind.BindComposer" 
 viewModel="@id('vm') @init('...InventoryVM')">
 <toolbar  width="100%">
  <toolbarbutton label="Add" onClick="@command('createNewItem')" />
  <toolbarbutton label="Delete" onClick="@command('deleteItem')" disabled="@load(empty vm.selected)"/>

  • line 5, assign a command method "deleteItem" to the delete button's onClick handler
  • line 5, "disabled="@(empty vm.selected)"" ensures that the delete button is functional only if an entry in the table has been selected

The ViewModel Class

public class InventoryVM {

    private Item selected;
    private List<Item> items;

    public void deleteItem() throws Exception{
        if (selected != null){
            String str = "The item with name \""
                         +"\" and model \""
                         +"\" will be deleted.";,"Confirm Deletion", Messagebox.OK|Messagebox.CANCEL, Messagebox.QUESTION, 
            new EventListener<event>(){
                public void onEvent(Event event) throws Exception {
                    if (event.getName().equals("onOK")){
                        items = getItems();
                        BindUtils.postNotifyChange(null, null, InventoryVM.this, "items");
                } ...

  • line 7, we decorate our deleteItem method with @Command so it can be wired as the onClick event handler in our added markup:
    <toolbarbutton label="Delete" onClick="@command('deleteItem')" />;
  • line 9, we go ahead with the deletion process only if an item is selected.
  • line 16, we show a Messagebox which prompts the user to confirm the deletion of the selected item.
  • line 20, if user clicks "OK", our program proceeds to delete the selected item.
  • line 23, we call BindUtils.postNotifyChange(String queueName, String queueScope, Object bean, String property) to update our inventory table. By giving the parameter queueScope a null value, the default desktop queue scope is used. The third and forth argument are given as such since we want to notify the Binder that property "items" in our InventoryVM instance has changed. The Binder would then update the UI (remove the item entry in the inventory table).

Wrap Up

The @NotifyChange annotation lets us update the UI through ZK MVVM's Binder to reflect changes made to the ViewModel properties. The notification is fired when the annotated method finishes executing. In our implementation, we attached an anonymous event listener class to a Messagebox. In this case, after deleteItem is executed, the annotation @NotifyChange("items") would falsely alert the Binder before the event handling is completed. A programmatic way to reflect state changes in ViewModel to the UI resolves this particular problem conveniently.

Next up, editing the entries with MVVM.


ZK Deverloper Reference


  1. Good Post. Can you the option to download the source code

    1. Hi, sorry about the delay in response. Please check out the reference section on You can view the ViewModel and ZUL code in their entirety by clicking the "View Source Code" button.

  2. I am trying to delete the iteam and showing same Dialogue box as u shown in ur example but even i added @NotifyChange annotation but my list is not refreshed even that particular row deleted from database.can u please explore wht can be issue

  3. As stated in the Wrap Up, @NotifyChange would alert the Binder of any change once the annotated method finishes execution. In the sample code here, the selected Item was not deleted after deleteItem finishes its execution; rather, DataService.getInstance().deleteItem(selected) was run within the anonymous event handler for the Messagebox. The whole point of this post is to demonstrate that you could use BindUtils.postNotifyChange to notify Binder of any change (thus refreshes the UI) at any point in your program, not constrained by the timing of @NotifyChange annotation.