ChangeWatcher

套件	mx.binding.utils
類別	public class ChangeWatcher
繼承	ChangeWatcher Object

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

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.

更多範例

Defining binding watchers

公用屬性

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	屬性		定義自
		constructor : Object 類別物件的參照或是特定物件實體的建構函數。	Object
		useWeakReference : Boolean Determines whether the reference to handler is strong or weak.	ChangeWatcher

公用方法

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	方法		定義自
		ChangeWatcher(access:Object, handler:Function, commitOnly:Boolean = false, next:ChangeWatcher = null) Constructor.	ChangeWatcher
		canWatch(host:Object, name:String, commitOnly:Boolean = false):Boolean [靜態] Lets you determine if the host exposes a data-binding event on the property.	ChangeWatcher
		getEvents(host:Object, name:String, commitOnly:Boolean = false):Object [靜態] Returns all binding events for a bindable property in the host object.	ChangeWatcher
		getValue():Object Retrieves the current value of the watched property or property chain, or null if the host object is null.	ChangeWatcher
		hasOwnProperty(name:String):Boolean 指出物件是否有已定義的指定屬性。	Object
		isPrototypeOf(theClass:Object):Boolean 指出 Object 類別的實體是否位於指定為參數的物件原型鏈中。	Object
		isWatching():Boolean Returns true if each watcher in the chain is attached to at least one change event.	ChangeWatcher
		propertyIsEnumerable(name:String):Boolean 指出指定的屬性是否存在，以及是否可列舉。	Object
		reset(newHost:Object):void Resets this ChangeWatcher instance to use a new host object.	ChangeWatcher
		setHandler(handler:Function):void Sets the handler function.	ChangeWatcher
		setPropertyIsEnumerable(name:String, isEnum:Boolean = true):void 為迴圈作業設定動態屬性的可用性。	Object
		toLocaleString():String 傳回代表此物件的字串，根據地區特定慣例進行格式化。	Object
		toString():String 會傳回指定之物件的字串形式。	Object
		unwatch():void Detaches this ChangeWatcher instance, and its handler function, from the current host.	ChangeWatcher
		valueOf():Object 會傳回指定之物件的基本值。	Object
		watch(host:Object, chain:Object, handler:Function, commitOnly:Boolean = false, useWeakReference:Boolean = false):ChangeWatcher [靜態] Creates and starts a ChangeWatcher instance.	ChangeWatcher

屬性詳細資訊

useWeakReference

屬性

public var useWeakReference:Boolean

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

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.

預設值為 false。

建構函式詳細資料

()

建構函式

public function ChangeWatcher(access:Object, handler:Function, commitOnly:Boolean = false, next:ChangeWatcher = null)

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

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.

參數

	`access:Object`

	`handler:Function`

	`commitOnly:Boolean` (default = `false`)

	`next:ChangeWatcher` (default = `null`)

方法詳細資訊

canWatch

()

方法

public static function canWatch(host:Object, name:String, commitOnly:Boolean = false):Boolean

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

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.

參數

	`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.

傳回值

Boolean — true if host exposes any change events on name.

getEvents

()

方法

public static function getEvents(host:Object, name:String, commitOnly:Boolean = false):Object

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

Flash Player 9, AIR 1.1

Returns all binding events for a bindable property in the host object.

參數

	`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.

傳回值

Object — Object of the form { eventName: isCommitting, ... } containing all change events for the property.

getValue

()

方法

public function getValue():Object

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

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

傳回值

Object — The current value of the watched property or property chain.

isWatching

()

方法

public function isWatching():Boolean

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

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.

傳回值

Boolean — true if each watcher in the chain is attached to at least one change event.

reset

()

方法

public function reset(newHost:Object):void

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

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.

參數

newHost:Object — The new host of the property. See the watch() method for more information.

setHandler

()

方法

public function setHandler(handler:Function):void

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

Flash Player 9, AIR 1.1

Sets the handler function.

參數

handler:Function — The handler function. This argument must not be null.

unwatch

()

方法

public function unwatch():void

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

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

()

方法

 public static function watch(host:Object, chain:Object, handler:Function, commitOnly:Boolean = false, useWeakReference:Boolean = false):ChangeWatcher

語言版本:

ActionScript 3.0

產品版本:

Flex 3

執行階段版本:

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).

參數

	`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.

傳回值

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.

相關 API 元素

mx.events.PropertyChangeEvent

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ChangeWatcher - AS3 Flex

類別 x

useWeakReference

ChangeWatcher

canWatch

getEvents

getValue

isWatching

reset

setHandler

unwatch

watch