From Documentation


  • Demonstration: N/A
  • Java API: Fragment
  • JavaScript API: Fragment
  • Style Guide: N/A
    • Available for ZK:
    • ee.png


    Fragment is a ZK component which developers can combine native HTML elements with ZK data binding syntax to make the static page to be dynamic.


    To manipulate HTML elements dynamically, ZK supports several ways in addition to this component. Please refer to ZK_Developer's_Reference/UI_Patterns/HTML_Tags for more details.


    ZKComRef Fragment Example.png

        <fragment viewModel="@id('vm') @init('org.zkoss.fragment.demo.VM2')" validationMessages="@id('vmsgs')"
                  form="@id('fx') @load(vm) @save(vm, before='submit') @validator(vm.formValidator)"
                  prop1="@bind(fx.prop1)" prop1err="@bind(vmsgs['fkey1'])"
                  prop2="@bind(fx.prop2)" prop2err="@bind(vmsgs['fkey2'])"><![CDATA[
            <p><input type="text" value="@bind(prop1)"/><span textContent="@load(prop1err)"/></p>
            <p><input type="text" value="@bind(prop2)"/><span textContent="@load(prop2err)"/></p>
            <button onclick="@command('submit')">Submit</button>

    Data Binding

    With Fragment Component, you can bind the properties of ViewModel. For instance, you can use ZK MVVM data binding to access the ViewModel on the native HTML elements.

    Enclose with CDATA

    Remember to mark the fragment content with the CDATA section to avoid being parsing by server-side binder and causes problems:


    Supported Bindings

    These are the supported annotations:

    • @save
     syntax: @save([limited EL-expression])
    • @load
     syntax: @load(limited EL-expression)
    • @bind
     syntax: @bind(limited EL-expression)
    • @command
     syntax: @command(mybean.myproperty, [arbitraryKey]=[limited EL-expression])
    • @global-command
     syntax: @global-command(mybean.myproperty, [arbitraryKey]=[limited EL-expression])

    Limited EL-expression

    Inside a fragment, it only supports partially, limited data binding expression including bean dot notation, arithmetic operator, !, and ==

    Put HTML as text content

    This component also provides a virtual textContent attribute for HTML elements to insert data into the tag.

        <fragment viewModel="@id('vm') @init('org.zkoss.zktest.test2.F85_ZK_3681_Command_VM')"
                <input type="checkbox" onchange="@command('onCheck', checked=event.checked)" />
                Check this checkbox: <span textContent="@load(status)"/>
                <button onclick="@global-command('callGlobal', text='Hello', num=1)">Call global (1)</button>
                <button onclick="@global-command('callGlobal', text='World', num=2)">Call global (2)</button>

    Shadow Elements

    In this example, we use if and forEach tags together for condition and collection rendering.

        <fragment viewModel="@id('vm') @init('org.zkoss.zktest.test2.F85_ZK_3681_Shadow_VM')"
                <h1>My Issue List</h1>
                    <forEach items="@load(issues)">
                        <!-- There's a pre-defined variable "each" for convenience. -->
                            <!-- @bind(each) is wrong because each is just a temp variable in loops. -->
                            <input type="checkbox" checked="@load(each.isDone)" />
                            <if test="@load(each.isDone)">
                                <strike>[<span textContent="@load("/>]
                                <span textContent="@load(each.description)"/></strike>
                            <!-- No else for now. -->
                            <if test="@load(!each.isDone)">
                                [<span textContent="@load("/>]
                                <span textContent="@load(each.description)"/>

    Data Validation

    Server-side Property/Form Validation

    To ensure data is correct and useful, we can leverage ZK's validators.

        <fragment viewModel="@id('vm') @init('org.zkoss.fragment.demo.VM1')" validationMessages="@id('vmsgs')"
                  prop1="@bind(vm.prop1) @validator(vm.validator1)"
            <input type="text" value="@bind(prop1)"/>
            <span textContent="@load(prop1err)"/>

    You can get the invalid message by assigning a self-defined key as an alias. In order to access invalidate messages by HTML elements, you can simply bind the messages onto Fragment properties.

    Here we can use form-binding and form validators to validate all the fields.

        <fragment viewModel="@id('vm') @init('foo.BarVM')" validationMessages="@id('vmsgs')"
         form="@id('fx') @load(vm.currentUser) @save(vm.currentUser, before='submit') @validator('formBeanValidator', prefix='p_')"
         name="@bind(" nameerror="@bind(vmsgs['p_name'])"><![CDATA[
         <input type="text" value="@bind(name)"/><span textContent="@load(nameerror)"/>
         <button onclick="@command('submit')">Submit</button>

    Client-side Property Validation

    This component also provides a new @jsvalidator running at client side, accepting custom JavaScript functions for validation. The benefit is that there is no need to send requests to the server for each validation. However, since the validation logic will be exposed at client side, some simple check, such as empty checking or range checking, is recommended. The usage is like @validator but it is effective only when applying HTML elements.


     syntax: @jsvalidator(validation_function_name)

    The following is the definition of custom JavaScript function.

    ValidationFunction(val, vmsgs)
    * val: The input data.
    * vmsgs: 
       The validation message holder object. You can add a invalidate message by adding a new property. 
       If you want to clear the specific message, assign an empty string to the property.
    * Returns: Boolean. True if the data is valid.

    You can use an implicit object (vmsgs) to get the client-side invalid messages. The @jsvalidator has its own validation message holder not shared with server-side.

        <fragment viewModel="@id('vm') @init('foo.BarVM')" someprop="@bind(vm.prop1)"><![CDATA[
            <input type="text" value="@bind(someprop) @jsvalidator('validateExample')"/>
            <span textContent="@load(vmsgs['foo'])"/>
        <script type="text/javascript">
            function validateExample(val, vmsgs) {
                var isValid = someValidationProcess(val);
                vmsgs['foo'] = isValid ? '' : 'Invalid value';
                return isValid;

    The Differences Between @validator and @jsvalidator

    Catalogue @validator @jsvalidator
    Validate at Server side Client side
    ZK form validation Supported Not supported
    Validation message holder Initialized in validationMessages An implicit vmsgs object
    1. @validator relies on the server, while @jsvalidator relies on the browser.
    2. @jsvalidator does not support form validation.
    3. The validation message holders are not the same.

    For security concerns, we recommend you to use server-side @validator in most cases and choose client-side @jsvalidator if the validation needs an instant feedback such as password strength, number range, and so on.

    Event Handling

    The command of ViewModel can be invoked by attaching DOM events with @command or @global-command on HTML elements. Once the DOM event is triggered (i.g. clicked or changed), the command of ViewModel will be executed and receive the corresponding event object.

    You can get more details from the event object such as mouse cursor position, pressed keys, entered text, and selected text.

    ZK Event object DOM event
    MouseEvent onclick
    KeyEvent onkeydown
    InputEvent onchange
    CheckEvent onchange (checkbox)
    oninput (checkbox)
    SelectionEvent onselect
    DropEvent ondrop
    Event onblur
    • For further details about how to retrieve the event object, please refer to Retrieve Event Object directly.


    • content: specify the content of this component.
    • src: specify the URI of an external content file. The file encoding is assumed to be UTF-8.
    • recoverId: specify the recover ID.

    Supported Events

    Event Type
    Event: Event

    Represents an event sent back to the server caused by an offline recovery.

    Supported Children


    Use Cases

    Version Description Example Location
    8.5+ Data binding, Shadow elements Client Binding with ZK MVVM for your eyes only
    8.5+ Data validation, Event handling Advanced Usage of Fragment Component

    Version History

    Last Update : 2023/03/23

    Version Date Content
    8.5 2017/09/21 Add the new Fragment component

    Last Update : 2023/03/23

    Copyright © Potix Corporation. This article is licensed under GNU Free Documentation License.