eu.webtoolkit.jwt
Class JSlot

java.lang.Object
  eu.webtoolkit.jwt.JSlot

public class JSlot
extends java.lang.Object

A slot that is only implemented in client side JavaScript code.

This class provides a hook for adding your own JavaScript to respond to events.

Carefully consider the use of this. Not only is writing cross-browser JavaScript hard and tedious, but one must also be aware of possible security problems (see further), and ofcourse, the event handling will not be available when JavaScript is disabled or not present at all.

For some purposes, stateless slot implementations are not sufficient, since they do not allow state inspection. At the same time, the non-availability in case of disabled JavaScript may also be fine for some non-essential functionality (see for example the WSuggestionPopup widget), or when you simply do not care. For these situations a JSlot can be used to add client-side event handling.

The JavaScript code may be set (or changed) using the setJavaScript() method which takes a string that implements a JavaScript function with the following signature:

 function(sender, event) {
    // handle the event, and sender is a reference to the DOM element
    // which captured the event (and holds the signal). Therefore it
    // equivalent to the sender for a normal %Wt slot.
 
    // You can prevent the default action using:
    ${WT_CLASS}.cancelEvent(event);
    // (where ${WT_CLASS} should be the value of the WT_CLASS define
  }
 
 

In the JavaScript code, you may use WWidget#getJsRef() to obtain the DOM element corresponding to any WWidget, or WObject#getId() to obtain the DOM id. In addition you may trigger server-side events using the JavaScript WtSignalEmit function (see JSignal documentation). That's how far we can help you. For the rest you are left to yourself, buggy browsers and quirky JavaScript (http://www.quirksmode.org/ was a reliable companion to me) -- good luck.

Note that the slot object needs to live as long as you want the JavaScript to be executed by connected signals: when the slot is destroyed, the connection is destroyed just as with other signal/slot connections where the target object is deleted. This means that it is (almost?) always a bad idea to declare a JSlot on the stack.

Constructor Summary

JSlot()
Constructs a JavaScript-only slot within the parent scope.

JSlot(java.lang.String javaScript)
Constructs a JavaScript-only and sets the JavaScript code.

JSlot(java.lang.String javaScript, WWidget parent)
Constructs a JavaScript-only and sets the JavaScript code.

JSlot(WWidget parent)
Constructs a JavaScript-only slot within the parent scope.

Method Summary

void	exec() Executes the JavaScript code.
void	exec(java.lang.String object) Executes the JavaScript code.
void	exec(java.lang.String object, java.lang.String event) Executes the JavaScript code.
java.lang.String	execJs() Returns a JavaScript statement that executes the slot.
java.lang.String	execJs(java.lang.String object) Returns a JavaScript statement that executes the slot.
java.lang.String	execJs(java.lang.String object, java.lang.String event) Returns a JavaScript statement that executes the slot.
void	setJavaScript(java.lang.String js) Sets or modify the JavaScript code associated with the slot.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

JSlot

public JSlot(WWidget parent)

Constructs a JavaScript-only slot within the parent scope.

The JavaScript code block will reside within the scope of the given widget. By picking a long-lived parent, one may reuse a single block of JavasCript code for multiple widgets.

When parent = null, then the JavaScript will be inlined in each caller (possibly replicating the same JavaScript).

JSlot

public JSlot()

Constructs a JavaScript-only slot within the parent scope.

Calls this((WWidget)null)

JSlot

public JSlot(java.lang.String javaScript,
             WWidget parent)

Constructs a JavaScript-only and sets the JavaScript code.

See Also:

JSlot(WWidget parent), setJavaScript(String js)

JSlot

public JSlot(java.lang.String javaScript)

Constructs a JavaScript-only and sets the JavaScript code.

Calls this(javaScript, (WWidget)null)

Method Detail

setJavaScript

public void setJavaScript(java.lang.String js)

Sets or modify the JavaScript code associated with the slot.

When the slot is triggered, the corresponding function defined by javaScript is executed.

The JavaScript function takes two parameters and thus should look like:

 function(obj, event) {
          // ...
        }
   
 

The first parameter obj is a reference to the DOM element that generates the event. The event refers to the JavaScript event object.

See Also:

WWidget.getJsRef()

exec

public void exec(java.lang.String object,
                 java.lang.String event)

Executes the JavaScript code.

This executes the JavaScript code in the same way as when triggered by a EventSignal. This function returns immediately, and execution of the JavaScript code is deferred until after the event handling.

The arguments are the "object, event" arguments of the JavaScript event callback function.

See Also:

setJavaScript(String js)

exec

public final void exec()

Executes the JavaScript code.

Calls exec("null", "null")

exec

public final void exec(java.lang.String object)

Executes the JavaScript code.

Calls exec(object, "null")

execJs

public java.lang.String execJs(java.lang.String object,
                               java.lang.String event)

Returns a JavaScript statement that executes the slot.

This returns the JavaScript code to execute the slot.

The arguments are the "object, event" arguments of the JavaScript event callback function.

See Also:

exec(String object, String event)

execJs

public final java.lang.String execJs()

Returns a JavaScript statement that executes the slot.

Returns execJs("null", "null")

execJs

public final java.lang.String execJs(java.lang.String object)

Returns a JavaScript statement that executes the slot.

Returns execJs(object, "null")