Browser Information and Control

To retrieve the information about the client, you can register an event listener for the onClientInfo event to a root component. To control the behavior of the client, you can use the utilities in the Clients class.

Browser Information

Sometimes an application needs to know the client's information, such as time zone. Then, you can add an event listener for the onClientInfo event. Once the event is added, the client will send back an instance of the ClientInfoEvent class, from which you can retrieve the information of the client.

For example,

<grid onClientInfo="onClientInfo(event)">
    <rows>
        <row>Time Zone <label id="tm"/></row>
        <row>Screen <label id="scrn"/></row>
    </rows>

    <zscript>
     void onClientInfo(ClientInfoEvent evt) {
         tm.setValue(evt.getTimeZone().toString());
         scrn.setValue(
             evt.getScreenWidth()+"x"+evt.getScreenHeight()+"x"+evt.getColorDepth());
     }
    </zscript>
</grid>

Notice that the onClientInfo event is meaningful only to the root component (aka., a component without any parent).

The client information is not stored by ZK, so you have to store it manually if necessary. Since a session is associated with the same client, you can store the client info in the session's attribute.

For example, we coud use it to control the default time zone.

 session.setAttribute("org.zkoss.web.preferred.timeZone", event.getTimeZone());

Notice that the onClientInfo event is sent from the client after the UI is rendered at the client. Thus, if some of your component's data depends on the client's info, say, screen resolution, it is better to handle it (say, adjust UI's size) when the onClientInfo event is received.

If it is, though rarely, too late (i.e., it has to be done at beginning), you could ask the client to re-send the request again with Executions.sendRedirect(String). For example,

 import org.zkoss.util.TimeZones;
 ...
  if (!TimeZones.getCurrent().equals(event.getTimeZone()) {
     session.setAttribute("org.zkoss.web.preferred.timeZone", event.getTimeZone()); //update to the session
     Executions.sendRedirect(null); //ask to re-send (i.e., redo)
  }

---

Browser Control

Clients has utilities to control the client's visual presentation (more precisely, the browser window), such as printing, submitting, resizing and so on. For example, you can scroll the browser window (aka., the desktop) as follows.

 Clients.scrollBy(100, 0);

Here we describe some special controls that are worth to notice. For complete functionality, please refer to Clients.

Prevent User from Closing a Browser Window

In some situation, you might want to confirm a user when he tries to close the window or browse to another URL. It can be done by the use of Clients.confirmClose(String).

For example, when a user is composing a mail that is not sent or saved yet.

 if (mail.isDirty()) {
     Clients.confirmClose("Your message has not been sent.\nDiscard your message?");
 } else {
     Clients.confirmClose(null); //reset. no more confirmation.
 }

As shown, it is done by passing the warning message to the client with Clients.confirmClose(String). Then, a confirmation dialog is shown up when the user tries to close the browser window, reload, or browse to another URL:

To disable the confirmation, just invoke Clients.confirmClose(String) with null.

Notify User Component under Processing

Sometimes a request takes long to process, and it is better to notice the user that it is under processing. It can be done by use of Clients.showBusy(Component, String), if only a component is not accessible, or Clients.showBusy(String) if the whole browser is not accessible. For example,

showBusy(grid, "Loading data...");

After the loading is completed, you could invoke Clients.clearBusy(Component) (or Clients.clearBusy())to clean it up. For more information, please refer to the Use Echo Events section.

Log the Message to Browser

[since 5.0.8]

In additions to logging messages to the console, you could log the messages to the browser for debugging by use of Clients.log(String). For example,

//in Java
void doSomething() {
   Clients.log("doSomething called");
}

Control in JavaScript

If you are familiar with JavaScript, you could have more control by sending any JavaScript code to the client for evaluation. It can be done by preparing the JavaScript code in AuInvoke or AuScript, and then sent back to client by calling Clients.response(AuResponse).

For example, we could use AuScript to inject any code, while AuInvoke is better if you want to invoke a function of a client-side widget.

Clients.response(new AuScript(null, "alert('Hello, Client')"));

For client-side API, please refer to JavaScript API.

Version History

Version	Date	Content
5.0.8	June, 2010	Clients.log(String) was introduced.