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Flash Player 6.
myObject.watch(prop,callback[,userData] )
prop A string indicating the name of the object property to watch.
callback The function to invoke when the watched property changes. This parameter is a function object, not a function name as a string. The form of callback is callback(prop, oldval, newval, userData).
userData An arbitrary piece of ActionScript data that is passed to the callback method. If the userData parameter is omitted, undefined is passed to the callback method. This parameter is optional.
A value of true if the watchpoint is created successfully; otherwise, returns a false value.
Method; registers an event handler to be invoked when a specified property of an ActionScript object changes. When the property changes, the event handler is invoked with myObject as the containing object. You must return the new value from the Object.watch() method, or the watched object property is assigned a value of undefined.
A watchpoint can filter (or nullify) the value assignment, by returning a modified newval (or oldval). If you delete a property for which a watchpoint has been set, that watchpoint does not disappear. If you later recreate the property, the watchpoint is still in effect. To remove a watchpoint, use the Object.unwatch method.
Only a single watchpoint may be registered on a property. Subsequent calls to Object.watch() on the same property replace the original watchpoint.
The Object.watch() method behaves similarly to the Object.watch() function in Netscape JavaScript 1.2 and later. The primary difference is the userData parameter, which is a Flash addition to Object.watch() that Netscape Navigator does not support. You can pass the userData parameter to the event handler and use it in the event handler.
The Object.watch() method cannot watch getter/setter properties. Getter/setter properties 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, Object.watch() needs to evaluate a property in order to fire watchpoints on it. To work with a getter/setter property, Object.watch() needs to evaluate the property constantly, which is inefficient.
Generally, ActionScript predefined properties, such as _x, _y, _width and _height, are getter/setter properties, and thus cannot be watched with Object.watch().
This example shows a CheckBox component with methods that set the label or value of each check box instance:
myCheckBox1.setValue(true);
myCheckBox1.setLabel("new label");
...
It's convenient to think of the value and label of a check box as properties. It's possible to use Object.watch() to make accessing the value and label look like property access rather than method invocation, as in the following:
// Define constructor for (and thus define) CheckBox class
function CheckBox() {
...
this.watch('value', function (id, oldval, newval){
...
});
this.watch('label', function(id, oldval, newval){
...
});
}
When the value or label property is modified, the function specified by the component is invoked to perform any tasks needed to update the appearance and state of the component. The following example invokes an Object.watch() method to notify the component that the variable has changed, causing the component to update its graphical representation.
myCheckBox1.value = false;
This syntax is more concise than the former syntax:
myCheckBox1.setValue(false);
Object.addProperty(), Object.unwatch()
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