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A bandbox is a special text box that embeds a customizable popup window (aka., a dropdown window). Like comboboxes, a bandbox consists of an input box and a popup window. The popup window is opened automatically, when a user presses Alt+DOWN or clicks the magnifier button.

Unlike comboboxes, the popup window of a bandbox could be anything. It is designed to give developers the maximal flexibility. A typical use is to represent the popup window as a search dialog.


ZKComRef Bandbox Example.png

<bandbox id="bd">
				<textbox />
			<listbox width="200px"
					<listheader label="Name" />
					<listheader label="Description" />
					<listcell label="John" />
					<listcell label="CEO" />
					<listcell label="Joe" />
					<listcell label="Engineer" />
					<listcell label="Mary" />
					<listcell label="Supervisor" />

Mouseless Entry bandbox

  • Alt+DOWN to pop up the list.
  • Alt+UP or ESC to close the list.


The Close Method

A popup window could contain any components, so it is the developer’s job to close the popup and copy any needed value from it.

<listbox width="200px"
   onSelect="bd.value=self.selectedItem.label; bd.close();">

In the above example, we copy the selected item's label to the bandbox, and then close the popup.


ZKComRef Bandbox Autodrop.PNG

By default, the popup window won't be opened until user clicks the button, or presses Alt+DOWN on the keyboard. However, you can set the autodrop property to true and as soon as the user types a character the popup will be opened. This is helpful for novice users, but it might be annoying for experienced users.

	<bandbox id="bd" autodrop="true">

The onOpen Event

If the user opens the popup window the onOpen event is sent to the application. By using the fulfill attribute with the onOpen value as shown below, you can defer the creation of the popup window.

<bandbox id="test">
    <bandpopup fulfill="test.onOpen">

Alternatively, you can prepare the popup window in Java by listening to the onOpen event, as depicted below.

	<bandbox id="band" onOpen="prepare()"/>
	     void prepare() 
	         if (band.getPopup() == null) {
	             //create child elements

The onChanging Event

Since a bandbox is also a text box, you are also able to listen to an onChanging event. By listening to this event, you can manipulate the popup window in any fashion. The code below illustrates capturing the user key and displaying information accordingly.

	<bandbox id="band" autodrop="true" onChanging="suggest()"/>
	     void suggest() 
	         if (event.value.startsWith("A")) {
	             //do something
	         } else if (event.value.startsWith("B")) {
	             //do another

Notice that, when the onChanging event is received, the content of the bandbox has not changed. Therefore, you cannot use the value property of the bandbox. Instead, you should use the value property of the event (org.zkoss.zk.ui.event.InputEvent).


You could specify what value to accept for input controls by the use of the constraint property. It could be a combination of no empty, and/or a regular expression.

To specify two or more constraints, use comma to separate them as follows.

<bandbox constraint="no empty,/^A/"/>

To specify a regular expression, you may have to use the character / to enclose the regular expression as follows.

<bandbox constraint="/^A/"/>


  • The above statement is XML, so do not use \\ to specify a backslash. However typing \\ is necessary, if writing in Java.
new Bandbox().setConstraint("/.+@.+\\.[a-z]+/");
  • You are allowed to mix regular expressions with other constraints by separating them with a comma.

If you prefer to display different message to the default one, you can append the error message to the constraint with a colon.

<bandbox constraint="/^A/: only allowed the item start with A"/>


  • The error message, if specified, must be the last element and start with colon.
  • To support multiple languages, you could use the 「l」 function as depicted in the Internationalization chapter.
<bandbox constraint="/^A/: ${c:l('err.startwith.required')}"/>


Since 8.6.2 Specify the sclass name of the Bandbox button icon. For built-in icon, please see ZK_Component_Reference/Base_Components/LabelImageElement.

Inherited Functions

Please refer to Textbox for inherited functions.

Supported Events

Event Type
Event: OpenEvent

Denotes user has opened or closed a component. Note: unlike onClose, this event is only a notification. The client sends this event after opening or closing the component.

Supported Molds

Available molds of a component are defined in lang.xml embedded in zul.jar.

Bandbox mold default.png
Bandbox mold rounded.png

Since 5.0.0

Supported Children

* Bandpopup 

Use Cases

Version Description Example Location

Version History

Last Update : 2022/02/21

Version Date Content

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