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.
[static]
Creates and starts a ChangeWatcher instance.
ChangeWatcher
Property Detail
useWeakReference
property
public var useWeakReference:Boolean
Language Version :
ActionScript 3.0
Product Version :
Flex 3
Runtime Versions :
Flash Player 9, AIR 1.1
Determines whether the reference to handler
is strong or weak.
A strong reference (the default) prevents
handler from being garbage-collected.
A weak reference does not.
The default value is false.
Constructor Detail
ChangeWatcher
()
Constructor
public function ChangeWatcher(access:Object, handler:Function, commitOnly:Boolean = false, next:ChangeWatcher = null)
Language Version :
ActionScript 3.0
Product Version :
Flex 3
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.
public static function canWatch(host:Object, name:String, commitOnly:Boolean = false):Boolean
Language Version :
ActionScript 3.0
Product Version :
Flex 3
Runtime Versions :
Flash Player 9, AIR 1.1
Lets you determine if the host exposes a data-binding event
on the property.
NOTE: Property chains are not supported by the canWatch() method.
They are supported by the watch() method.
Parameters
host:Object — The host of the property.
See the watch() method for more information.
name:String — The name of the property.
See the watch() method for more information.
commitOnly:Boolean (default = false) — Set to 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.
getEvents
()
method
public static function getEvents(host:Object, name:String, commitOnly:Boolean = false):Object
Language Version :
ActionScript 3.0
Product Version :
Flex 3
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) — Controls inclusion of non-committing
change events in the returned value.
Returns
Object — Object of the form { eventName: isCommitting, ... }
containing all change events for the property.
getValue
()
method
public function getValue():Object
Language Version :
ActionScript 3.0
Product Version :
Flex 3
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:
Object — The current value of the watched property or property chain.
isWatching
()
method
public function isWatching():Boolean
Language Version :
ActionScript 3.0
Product Version :
Flex 3
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.
reset
()
method
public function reset(newHost:Object):void
Language Version :
ActionScript 3.0
Product Version :
Flex 3
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.
setHandler
()
method
public function setHandler(handler:Function):void
Language Version :
ActionScript 3.0
Product Version :
Flex 3
Runtime Versions :
Flash Player 9, AIR 1.1
Sets the handler function.
Parameters
handler:Function — The handler function. This argument must not be null.
unwatch
()
method
public function unwatch():void
Language Version :
ActionScript 3.0
Product Version :
Flex 3
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.
watch
()
method
public static function watch(host:Object, chain:Object, handler:Function, commitOnly:Boolean = false, useWeakReference:Boolean = false):ChangeWatcher
Language Version :
ActionScript 3.0
Product Version :
Flex 3
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.
The host maintains a list of handlers to invoke
when prop changes.
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) — Set to 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) — (default = false) Determines whether
the reference to handler is strong or weak. A strong
reference (the default) prevents handler from being
garbage-collected. A weak reference does not.
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.
Object