MACROMEDIA FLASH MX 2004-ACTIONSCRIPT LANGUAGE Reference page 677

The
Object.watch()
1.2 and later. The primary difference is the
that Netscape Navigator does not support. You can pass the
Object.watch()
parameter to the event handler and use it in the event handler.
The
Object.watch()
operate through lazy evaluation— the value of the property is not determined until the property is
actually queried. Lazy evaluation is often efficient because the property is not constantly updated;
it is, rather, evaluated when needed. However,
determine whether to invoke the
needs to evaluate the property constantly, which is inefficient.
Object.watch()
Generally, predefined ActionScript properties, such as
setter properties and cannot be watched with
Example
The following example uses
limit:
// Create a new object
var myObject:Object = new Object();
// Add a property that tracks speed
myObject.speed = 0;
// Write the callback function to be executed if the speed property changes
var speedWatcher:Function = function(prop, oldVal, newVal, speedLimit) {
// Check whether speed is above the limit
if (newVal > speedLimit) {
trace ("You are speeding.");
}
else {
trace ("You are not speeding.");
}
// Return the value of newVal.
return newVal;
}
// Use watch() to register the event handler, passing as parameters:
// - the name of the property to watch: "speed"
// - a reference to the callback function speedWatcher
// - the speedLimit of 55 as the userData parameter
myObject.watch("speed", speedWatcher, 55);
// set the speed property to 54, then to 57
myObject.speed = 54; // output: You are not speeding
myObject.speed = 57; // output: You are speeding
// unwatch the object
myObject.unwatch("speed");
myObject.speed = 54; // there should be no output
See also
Object.addProperty(),
method behaves similarly to the
userData
method cannot watch getter/setter properties. Getter/setter properties
function. To work with a getter/setter property,
callback
to check whether the
watch()
Object.unwatch()
Object.watch()
parameter, which is a Flash addition to
needs to evaluate a property to
Object.watch()
, ,
_x _y _width
.
Object.watch()
property exceeds the speed
speed
function in JavaScript
userData
, and , are getter/
_height
Object.watch() 677