About Lance Lu

ZK in Action: MVVM – Working Together with ZK Client API

In the previous posts we’ve implemented the following functionalities with ZK’s MVVM:

A key distinction between ZK MVVM and ZK MVC implementation wise is that we do not access and manipulate the UI components directly in the controller(ViewModel) class. In this post, we’ll see how we can delegate some of the UI manipulation to client side code, as well as how to pass parameters from View to ViewModel.

Objective

Build an update function to our simple inventory CRUD feature. Users can edit-in-place entries in the table and given the choice to update or discard the changes made. Modified entries are highlighted in red.

ZK Features in Action

  • ZK Client-side APIs
  • ZK Style Class
  • MVVM : Pass Parameters from View to ViewModel

Implementation in Steps  

Enable In-place editing in Listbox so we can edit entries:

<listcell>
       <textbox inplace="true" value="@load(each.name)" ...</textbox>
   </listcell>
   ....
   <listcell>
       <doublebox inplace="true" value="@load(each.price)" ...</textbox>
   </listcell>
   ...
  • inplace=”true” renders input elements such as Textbox without their borders displaying them as plain labels; the borders appear only if the input element is selected
  • line 2, 6,”each” refers to each Item object in the data collection

Once an entry is edited we want to give users the option to Update or Discard the change. 
The Update and Discard buttons need to be visible only if user has made modifications on the Listbox entries. First we define JavaScript functions to show and hide the Update and Discard buttons:

<toolbar>
    ...
    <span id="edit_btns" visible="false" ...>
        <toolbarbutton label="Update" .../>
        <toolbarbutton label="Discard" .../>
    </span>
</toolbar>

    <script type="text/javascript">
        function hideEditBtns(){
     jq('$edit_btns').hide();
        }
  
        function showEditBtns(){ 
     jq('$edit_btns').show();
        }

    </script>
    ...
  • line 2, we wrap the Update and Discard and set visibility to false
  • line 9, 13, we define functions which hide and show the Update and Discard buttons respectively
  • line 11, 15, we make use of jQuery selector jq( ‘$edit_btns’) to retrieve the ZK widget whose ID is “edit_btns”; notice the selector pattern for a ZK widget ID is ‘$’, not ‘#’

When entries in the Listbox are modified, we’ll make the Update/Discard buttons visible and make the modified values red. Once either Update or Discard button is clicked, we’d like to hide the buttons again

Since this is pure UI interactions, we’ll make use of ZK’s client side APIs:

<style>
   .inputs { font-weight: 600; }
   .modified { color: red; }
</style>
...
    <toolbar xmlns:w="client" >
    ...
    <span id="edit_btns" visible="false" ...>
         <toolbarbutton label="Update" w:onClick="hideEditBtns()" .../>
         <toolbarbutton label="Discard" w:onClick="hideEditBtns()" .../>
    </span>
    </toolbar>

    <script type="text/javascript">
        //show hide functions

        zk.afterMount(function(){
            jq('.inputs').change(function(){
            showEditBtns();
            $(this).addClass('modified');
     })
        });
    </script>
    ...
    <listcell>
       <doublebox inplace="true" sclass="inputs" value="@load(each.price)" ...</textbox>
   </listcell>
   ...
  • line 2, we specify a style class for our input elements (Textbox, Intbox, Doublebox, Datebox) and assign it to input elements’ sclass attribute, eg. line 26; sclass defines style class for ZK widgets
  • line 18~20, we get all the input elements by matching their sclass name and assign an onChange event handler. Once the value in an input element is changed, the Update/Discard buttons will become visible and the modified value will be highlighted in red.
  • line 17, zk.afterMount is run when ZK widgets are created
  • line 6, we specify the client namespace so we can register client side onClick event listeners with the syntax “w:onClick”. Note we can still register our usual onClick event listener that’s handled at the server simultaneously.
  • line 9, 10, we assign client side onClick event listener; the hideEditBtns function would be called to make the buttons invisible again

Define a method to store the modified Item objects into a collection so the changes could be updated in batch if user choose to do so:

public class InventoryVM {

    private HashSet<Item> itemsToUpdate = new HashSet<item>();
    ...

    @Command
    public void addToUpdate(@BindingParam("entry") Item item){
        itemsToUpdate.add(item);
    }
  • line 6, we annotate this method as a command method so it can be invoked from View
  • line 7, @BindingParam(“entry”) Item item binds an arbitrarily named parameter called “entry”; we anticipate the parameter would be of type Item

Create a method to update the changes made in View to the Data Model

public class InventoryVM {

    private List<Item> items;
    private HashSet<Item> itemsToUpdate = new HashSet<item>();
    ...

    @NotifyChange("items")
    @Command
    public void updateItems() throws Exception{
        for (Item i : itemsToUpdate){
            i.setDatemod(new Date());
            DataService.getInstance().updateItem(i);
        }
        itemsToUpdate.clear();
        items = getItems();
    }


When modifications are made on Listbox entries, invoke the addToUpdate method and pass to it the edited Item object which in turn is saved to the itemsToUpdate collection

<listitem>
 <listcell>
  <doublebox value="@load(each.price) 
                @save(each.name, before='updateItems')"  
                onChange="@command('addToUpdate',entry=each)" />
 </listcell>
 ...
</listitem>
  • @save(each.name, before=’updateItems’) ensures that modified values are not saved unless updateItems is called (ie. when user click the “Update” button)

Finally, when user clicks Update, we call the updateItems method to update changes to Data Model. If Discard is clicked, we call getItems to refresh the Listbox without applying any changes

...
 <toolbarbutton label="Update" onClick="@command('updateItems')" .../>
 <toolbarbutton label="Discard" onClick="@command('getItems')" .../>
 ...

In a Nutshell

  • Under the MVVM pattern we strive to keep the ViewModel code independent of any View components
  • Since we don’t have direct reference to the UI components in the ViewModel code, we can delegate the UI manipulation (in our sample code, show/hide, style change) code to the client using ZK’s client side APIs
  • We can make use of jQuery selectors and APIs at ZK client side
  • We can easily pass parameters from View to ViewModel with @BindingParam

Next up, we’ll go over a bit more on ZK Styling before we tackle the MVVM validators and converters.  

ViewModel (ZK in Action[0]~[3]):

public class InventoryVM {

 private List<Item> items;
 private Item newItem;
 private Item selected;
 private HashSet<Item> itemsToUpdate = new HashSet<Item>();
 
 public InventoryVM(){}
 
 //CREATE
 @NotifyChange("newItem")
 @Command
 public void createNewItem(){
  newItem = new Item("", "",0, 0,new Date());
 }
 
 @NotifyChange({"newItem","items"})
 @Command
 public void saveItem() throws Exception{
  DataService.getInstance().saveItem(newItem);
  newItem = null;
  items = getItems();
 }
  
 @NotifyChange("newItem")
 @Command
 public void cancelSave() throws Exception{
  newItem = null;
 }
 
 //READ
 @NotifyChange("items")
 @Command
 public List<Item> getItems() throws Exception{
  items = DataService.getInstance().getAllItems();
  for (Item j : items){
   System.out.println(j.getModel());
  }
  Clients.evalJavaScript("zk.afterMount(function(){jq('.inputs').removeClass('modified').change(function(){$(this).addClass('modified');showEditBtns();})});"); //how does afterMount work in this case?
  return items;
 }
 
 //UPDATE
 @NotifyChange("items")
 @Command
 public void updateItems() throws Exception{
  for (Item i : itemsToUpdate){
   i.setDatemod(new Date());
   DataService.getInstance().updateItem(i);
  }
  itemsToUpdate.clear();
  items = getItems();
 }
 
 @Command
 public void addToUpdate(@BindingParam("entry") Item item){
  itemsToUpdate.add(item);
 }
 
 //DELETE
 @Command
 public void deleteItem() throws Exception{
  if (selected != null){
  
   String str = "The item with name \""+selected.getName()+"\" and model \""+selected.getModel()+"\" will be deleted.";
   Messagebox.show(str,"Confirm Deletion", Messagebox.OK|Messagebox.CANCEL, Messagebox.QUESTION, 
    new EventListener<Event>(){
     @Override
     public void onEvent(Event event) throws Exception {
      if (event.getName().equals("onOK")){
       DataService.getInstance().deleteItem(selected);
       items = getItems();
       BindUtils.postNotifyChange(null, null, InventoryVM.this, "items");
      }
     }
   });
   
  } else {
   Messagebox.show("No Item was Selected");
  } 
 }
 

 public Item getNewItem() {
  return newItem;
 }

 public void setNewItem(Item newItem) {
  this.newItem = newItem;
 }

 public Item getselected() {
  return selected;
 }

 public void setselected(Item selected) {
  this.selected = selected;
 }
}

View (ZK in Action[0]~[3]):

<zk>
 <style>
  .z-toolbarbutton-cnt { font-size: 17px;} .edit-btns {border: 2px
  solid #7EAAC6; padding: 6px 4px 10px 4px; border-radius: 6px;}
  .inputs { font-weight: 600; } .modified { color: red; }
 </style>
 <script type="text/javascript">
  function hideEditBtns(){ jq('$edit_btns').hide(); }

  function showEditBtns(){ jq('$edit_btns').show(); }

  zk.afterMount(function(){ jq('.inputs').change(function(){
  $(this).addClass('modified'); showEditBtns(); }) });
 </script>
 <window apply="org.zkoss.bind.BindComposer"
  viewModel="@id('vm') @init('lab.sphota.zk.ctrl.InventoryVM')"
  xmlns:w="client">
  <toolbar width="100%">
   <toolbarbutton label="Add"
    onClick="@command('createNewItem')" />
   <toolbarbutton label="Delete"
    onClick="@command('deleteItem')"
    disabled="@load(empty vm.selected)" />
   <span id="edit_btns" sclass="edit-btns" visible="false">
    <toolbarbutton label="Update" 
     onClick="@command('updateItems')" w:onClick="hideEditBtns()"/>
    <toolbarbutton label="Discard"
     onClick="@command('getItems')" w:onClick="hideEditBtns()" />
   </span>
  </toolbar>
  <groupbox mold="3d"
   form="@id('itm') @load(vm.newItem) @save(vm.newItem, before='saveItem')"
   visible="@load(not empty vm.newItem)">
   <caption label="New Item"></caption>
   <grid width="50%">
    <rows>
     <row>
      <label value="Item Name" width="100px"></label>
      <textbox value="@bind(itm.name)" />
     </row>
     <row>
      <label value="Model" width="100px"></label>
      <textbox value="@bind(itm.model)" />
     </row>
     <row>
      <label value="Unit Price" width="100px"></label>
      <decimalbox value="@bind(itm.price)"
       format="#,###.00" constraint="no empty, no negative" />
     </row>
     <row>
      <label value="Quantity" width="100px"></label>
      <spinner value="@bind(itm.qty)"
       constraint="no empty,min 0 max 999: 
       Quantity Must be Greater Than Zero" />
     </row>
     <row>
      <cell colspan="2" align="center">
       <button width="80px" label="Save" mold="trendy"
        onClick="@command('saveItem')"  />
       <button width="80px" label="Cancel" mold="trendy"
        onClick="@command('cancelSave')" />
      </cell>
     </row>
    </rows>
   </grid>
  </groupbox>
  <listbox selectedItem="@bind(vm.selected)" model="@load(vm.items) ">
   <listhead>
    <listheader label="Name" sort="auto" hflex="2" />
    <listheader label="Model" sort="auto" hflex="1" />
    <listheader label="Quantity" sort="auto" hflex="1" />
    <listheader label="Unit Price" sort="auto" hflex="1" />
    <listheader label="Last Modified" sort="auto" hflex="2" />
   </listhead>
   <template name="model">
    <listitem>
     <listcell>
      <textbox inplace="true" width="110px" sclass="inputs"
       value="@load(each.name) @save(each.name, before='updateItems')"
       onChange="@command('addToUpdate',entry=each)">
      </textbox>
     </listcell>
     <listcell>
      <textbox inplace="true" width="110px" sclass="inputs" 
       value="@load(each.model) @save(each.model, before='updateItems')"
       onChange="@command('addToUpdate',entry=each)" />
     </listcell>
     <listcell>
      <intbox inplace="true" sclass="inputs" 
       value="@load(each.qty) @save(each.qty, before='updateItems')"
       onChange="@command('addToUpdate',entry=each)" />
     </listcell>
     <listcell>
      <doublebox inplace="true" sclass="inputs" format="###,###.00" 
       value="@load(each.price) @save(each.price, before='updateItems')"
       onChange="@command('addToUpdate',entry=each)" />
     </listcell>
     <listcell label="@load(each.datemod)" />
    </listitem>
   </template>
  </listbox>
 </window>
</zk>

Reference: ZK in Action [3] : MVVM – Working Together with ZK Client API from our JCG partner Lance Lu at the Tech Dojo blog.

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2 Responses to "ZK in Action: MVVM – Working Together with ZK Client API"

  1. Subodh Joshi says:

    As here you are using @bind for binding any field from java class.Let us suppose i am creating a istbox with he help of getItemRendered() method then in this case how we will bind? Do you give any such example

  2. ufuk says:

    Plus, you are weakening MVVM pattern by using Clients.evalJavaScript. You are directly aware of the UI and directly manipulating it. Any idea on how to do this another way?

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