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| | = Overview = | | = Overview = |
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| − | ZK allows applications to handle events at both server and client side. Handling events at the server side, as described in the previous sections, are more common, since the listeners can access the backend services directly. However, handling event at the client side improves the responsiveness. For example, it is better to be done with a client-side listener if you want to open the drop-down list when a comobox gains the focus. | + | ZK allows applications to handle events at both the server and client side. Handling events at the server side, as described in the previous sections, is more common, since the listeners can access the backend services directly. However, handling events at the client side improves the responsiveness. For example, it is better to be done with a client-side listener if you want to open the drop-down list when a combobox gains focus. |
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| − | The rule of thumb is to use server-side listeners first since it is easier, and then improve the responsiveness of the critical part, if any, with the client-side listener.
| + | A good rule of thumb is to use server-side listeners first since it is easier, and then improve the responsiveness of the critical part, if any, with the client-side listener. |
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| − | = Declare a Client-side Listener in a ZUL Page =
| + | For more information about handling events at the client, please refer to [[ZK Client-side Reference/General Control/Event Listening|ZK Client-side Reference: Event Listening]]. |
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| − | Declaring a client-side listener in a ZUL page is similar to declaring a server-side listener, except
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| − | # Use the client namespace, http://www.zkoss.org/2005/zk/client (aka., client)
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| − | # It is JavaScript
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| − | # Use <tt>this</tt> to reference to the target widget (while the event is referenced with <tt>event</tt>)
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| − | For example,
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| − | <syntax lang="xml">
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| − | <combobox xmlns:w="client" w:onFocus="this.open()"/>
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| − | </syntax>
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| − | Notice that EL expressions are allowed in the JavaScript code (for the client-side listener). Thus, it is straightforward to embed the server-side data to the client-side listener. For example,
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| − | <syntax lang="xml">
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| − | <window id="wnd" title="main">
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| − | <combobox xmlns:w="client" w:onFocus="zk.log('${wnd.title}')"/>
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| − | </window>
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| − | </syntax>
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| − | If you want to escape it, place a backslash between $ and {, such as <code>w:onFocus="zk.log('$\{wnd.title}')"</code>.
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| − | == The Relationship between Client and Server-side Event Listener ==
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| − | It is allowed to register both the client and server-side event listeners. They will be both invoked. Of course, the client-side listener is called first, and then the server-side listener. For example,
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| − | <syntax lang="xml">
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| − | <div>
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| − | <combobox xmlns:w="client" w:onFocus="this.open()"
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| − | onFocus='self.parent.appendChild(new Label("focus"))'/>
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| − | </div>
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| − | </syntax>
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| − | If you want to stop the event propagation such that the server won't receive the event, you could invoke <javadoc method="stop(_global_.Map)" directory="jsdoc">zk.Event</javadoc>. For example, the server-side listener won't be invoked in the following example:
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| − | <syntax lang="xml">
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| − | <div>
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| − | <combobox xmlns:w="client" w:onFocus="this.open(); event.stop();"
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| − | onFocus='self.parent.appendChild(new Label("focus"))'/>
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| − | </div>
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| − | </syntax>
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| − | = Declare a Client-side Listener in Java =
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| − | The other way to declare a client-side listener at the server is <javadoc method="setWidgetListener(java.lang.String, java.lang.String)">org.zkoss.zk.ui.Component</javadoc>. For example,
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| − | <syntax lang="java">
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| − | combobox.setWidgetListener("onFocus", "this.open()");
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| − | </syntax>
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| − | Notice that it is Java and running at the server.
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| − | Also notice that EL expressions are not allowed (i.e., not interpreted) if you assign it directly. It is because EL expressions are interpreted by ZK Loader when loading a ZUL page. However, it is easy to construct a string to any content you want with Java.
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| − | = Register a Client-side Listener in Client-Side JavaScript =
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| − | Listening an event at the client could be done by calling <javadoc directory="jsdoc" method="listen(_global_.Map, int)">zk.Widget</javadoc>. For example,
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| − | <syntax lang="xml">
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| − | <window>
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| − | <bandbox id="bb"/>
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| − | <script defer="true">
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| − | this.$f('bb').listen({onFocus: function () {this.open();}});
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| − | </script>
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| − | </window>
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| − | </syntax>
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| − | where
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| − | # <code>defer="true"</code> is required such that the JavaScript code will be evaluated after all widgets are created successfully. Otherwise, it is not able to retreive the bandbox (<code>bb</code>).
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| − | # <code>script</code> is a widget (unlike <code>zscript</code>), so <code>this</code> references to the <code>script</code> widget, rather than the parent.
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| − | # <javadoc directory="jsdoc" method="$f(_global_.String)">zk.Widget</javadoc> is equivalent to <javadoc method="getFellow(java.lang.String)">org.zkoss.zk.ui.Component</javadoc>, except it is a JavaScript method (accessible at the client).
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| − | =Version History=
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| − | {| border='1px' | width="100%"
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| − | ! Version !! Date !! Content
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| − | |}
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| | {{ZKDevelopersReferencePageFooter}} | | {{ZKDevelopersReferencePageFooter}} |
Client-side Event Listening
Overview
ZK allows applications to handle events at both the server and client side. Handling events at the server side, as described in the previous sections, is more common, since the listeners can access the backend services directly. However, handling events at the client side improves the responsiveness. For example, it is better to be done with a client-side listener if you want to open the drop-down list when a combobox gains focus.
A good rule of thumb is to use server-side listeners first since it is easier, and then improve the responsiveness of the critical part, if any, with the client-side listener.
For more information about handling events at the client, please refer to ZK Client-side Reference: Event Listening.