| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
The ChangeWatcher class defines utility methods
that you can use with bindable Flex properties.
These methods let you define an event handler that is executed
whenever a bindable property is updated.
public var useWeakReference:Boolean| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
(default = false) Determines whether the reference to the host
is strong or weak. A strong reference (the default) prevents
the host from being garbage-collected. A weak reference does
not.
public function ChangeWatcher(access:Object, handler:Function, commitOnly:Boolean = false, next:ChangeWatcher = null)| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
Constructor.
Not for public use. This method is called only from the watch() method.
See the watch() method for parameter usage.
Parameters public static function canWatch(host:Object, name:String, commitOnly:Boolean = false):Boolean| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
Lets you determine if the host exposes a data-binding event
on the property.
Parameters
| host:Object — The host of the property.
See the watch() method for more information.
|
| |
| name:String — The name of the property, or property chain.
See the watch() method for more information.
|
| |
| commitOnly:Boolean (default = false)true if the handler
should be called only on committing change events.
See the watch() method for more information.
|
Returns | Boolean — true if host exposes
any change events on name.
|
public static function getEvents(host:Object, name:String, commitOnly:Boolean = false):Object| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
Returns all binding events for a bindable property in the host object.
Parameters
| host:Object — The host of the property.
See the watch() method for more information.
|
| |
| name:String — The name of the property, or property chain.
See the watch() method for more information.
|
| |
| commitOnly:Boolean (default = false) |
Returns | Object — Object of the form { eventName: isCommitting, ... }
containing all change events for the property.
|
public function getValue():Object| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
Retrieves the current value of the watched property or property chain,
or null if the host object is null.
For example:
watch(obj, ["a","b","c"], ...).getValue() === obj.a.b.c
Returns | Object — The current value of the watched property or property chain.
|
public function isWatching():Boolean| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
Returns true if each watcher in the chain is attached
to at least one change event.
Note that the isWatching() method
varies with host, since different hosts may expose different change
events for the watcher's chosen property.
Returns | Boolean — true if each watcher in the chain is attached
to at least one change event.
|
public function reset(newHost:Object):void| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
Resets this ChangeWatcher instance to use a new host object.
You can call this method to reuse a watcher instance
on a different host.
Parameters
| newHost:Object — The new host of the property.
See the watch() method for more information.
|
public function setHandler(handler:Function):void| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
Sets the handler function.
Parameters
| handler:Function — The handler function. This argument must not be null.
|
public function unwatch():void| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
Detaches this ChangeWatcher instance, and its handler function,
from the current host.
You can use the reset() method to reattach
the ChangeWatcher instance, or watch the same property
or chain on a different host object.
public static function watch(host:Object, chain:Object, handler:Function, commitOnly:Boolean = false, useWeakReference:Boolean = false):ChangeWatcher| Language Version: | ActionScript 3.0 |
| Runtime Versions: | Flash Player 9, AIR 1.1 |
Creates and starts a ChangeWatcher instance.
A single ChangeWatcher instance can watch one property,
or a property chain.
A property chain is a sequence of properties accessible from
a host object.
For example, the expression
obj.a.b.c contains the property chain (a, b, c).
Parameters
| host:Object — The object that hosts the property or property chain
to be watched.
You can use the use the reset() method to change
the value of the host argument after creating
the ChangeWatcher instance.
|
| |
| chain:Object — A value specifying the property or chain to be watched.
Legal values are:
- A String containing the name of a public bindable property
of the host object.
- An Object in the form:
{ name: property name, getter: function(host) { return host[name] } }.
The Object contains the name of a public bindable property,
and a function which serves as a getter for that property. - A non-empty Array containing any combination
of the first two options.
This represents a chain of bindable properties
accessible from the host.
For example, to watch the property
host.a.b.c,
call the method as: watch(host, ["a","b","c"], ...).
Note: The property or properties named in the chain argument
must be public, because the describeType() method suppresses all information
about non-public properties, including the bindability metadata
that ChangeWatcher scans to find the change events that are exposed
for a given property.
However, the getter function supplied when using the { name, getter }
argument form described above can be used to associate an arbitrary
computed value with the named (public) property.
|
| |
| handler:Function — An event handler function called when the value of the
watched property (or any property in a watched chain) is modified.
The modification is signaled when any host object in the watcher
chain dispatches the event that has been specified in that host object's
[Bindable] metadata tag for the corresponding watched property.
The default event is named propertyChange.
The event object dispatched by the bindable property is passed
to this handler function without modification.
By default, Flex dispatches an event object of type PropertyChangeEvent.
However, you can define your own event type when you use the
[Bindable] metadata tag to define a bindable property.
|
| |
| commitOnly:Boolean (default = false)true if the handler should be
called only on committing change events;
set to false if the handler should be called on both
committing and non-committing change events.
Note: the presence of non-committing change events for a property is
indicated by the [NonCommittingChangeEvent(<event-name>)] metadata tag.
Typically these tags are used to indicate fine-grained value changes,
such as modifications in a text field prior to confirmation.
|
| |
| useWeakReference:Boolean (default = false) |
Returns | ChangeWatcher — The ChangeWatcher instance, if at least one property name has
been specified to the chain argument; null otherwise.
Note that the returned watcher is not guaranteed to have successfully
discovered and attached itself to change events, since none may have
been exposed on the given property or chain by the host.
You can use the isWatching() method to determine the
watcher's state.
|
See also
Object
Hide Inherited Public Properties
Show Inherited Public Properties