http://zhidao.baidu.com/question/80156523.html
[Bindable]public class TextAreaFontControl extends TextArea {}flex编译器自动创建一个事件名叫propertyChange用于所有的公有属性，这些属性可以作为绑定表达式的源。这种定义等同于[Bindable(event="propertyChange")]
http://www.cnblogs.com/jiayuan/archive/2010/01/04/1638797.html? 此文1描述了如何实现。
但是实际使用中发现类不是extend EventDispatcher 也可以设置属性为Bindable，那是怎么发事件的？
下文描述了内部机制，dynamic的加了函数，和xml的那些接口类似，使用中不会自动补全函数，
??????????? protected function group1_creationCompleteHandler(event:FlexEvent):void
?? ??? ??? ?{
?? ??? ??? ??? ?nd.addEventListener("propertyChange",onEvent);
?? ??? ??? ?}
http://blog.csdn.net/thinkinside/article/details/1880058
??? Flex中提供了[Bindable]标签，可以方便的实现数据绑定。但是其背后的原理是什么呢？可以用flash.utils.describeType这个工具来分析。
??? 假设有如下的类，对成员变量声明了数据绑定：
package?test
{
????import?mx.collections.ArrayCollection;
????
????public?class?BindablePropertity
????{
????????[Bindable]
????????public?var?list:ArrayCollection?=?new?ArrayCollection();
????}
}
用flash.utils.describeType输出的xml如下：
<
type?
name
="test::BindablePropertity"
?base
="Class"
?isDynamic
="true"
?isFinal
="true"
?isStatic
="true"
>
??
<
extendsClass?
type
="Class"
/>
??
<
extendsClass?
type
="Object"
/>
??
<
accessor?
name
="prototype"
?access
="readonly"
?type
="*"
?declaredBy
="Class"
/>
??
<
factory?
type
="test::BindablePropertity"
>
????
<
extendsClass?
type
="Object"
/>
????
<
implementsInterface?
type
="flash.events::IEventDispatcher"/>
????
<
method?
name
="hasEventListener"
?declaredBy
="test::BindablePropertity"
?returnType
="Boolean"
>
??????
<
parameter?
index
="1"
?type
="String"
?optional
="false"
/>
????
</
method
>
????
<
method?
name
="removeEventListener"
?declaredBy
="test::BindablePropertity"
?returnType
="void"
>
??????
<
parameter?
index
="1"
?type
="String"
?optional
="false"
/>
??????
<
parameter?
index
="2"
?type
="Function"
?optional
="false"
/>
??????
<
parameter?
index
="3"
?type
="Boolean"
?optional
="true"
/>
????
</
method
>
????
<
method?
name
="willTrigger"
?declaredBy
="test::BindablePropertity"
?returnType
="Boolean"
>
??????
<
parameter?
index
="1"
?type
="String"
?optional
="false"
/>
????
</
method
>
????
<
accessor?
name
="list"
?access
="readwrite"
?type
="mx.collections::ArrayCollection"
?declaredBy
="test::BindablePropertity"
>
??????
<
metadata?
name
="Bindable"
>
????????
<
arg?
key
="event"
?value
="propertyChange"
/>
??????
</
metadata
>
????
</
accessor
>
????
<
method?
name
="addEventListener"
?declaredBy
="test::BindablePropertity"
?returnType
="void"
>
??????
<
parameter?
index
="1"
?type
="String"
?optional
="false"
/>
??????
<
parameter?
index
="2"
?type
="Function"
?optional
="false"
/>
??????
<
parameter?
index
="3"
?type
="Boolean"
?optional
="true"
/>
??????
<
parameter?
index
="4"
?type
="int"
?optional
="true"
/>
??????
<
parameter?
index
="5"
?type
="Boolean"
?optional
="true"
/>
????
</
method
>
????
<
method?
name
="dispatchEvent"
?declaredBy
="test::BindablePropertity"
?returnType
="Boolean"
>
??????
<
parameter?
index
="1"
?type
="flash.events::Event"
?optional
="false"
/>
????
</
method
>
??
</
factory
>
</
type
>
可以看出，增加了[Bindable]声明后，相当于这个类实现了IEventDispatcher接口，并且在数据发生变化时会分发propertyChange事件。这样，其他监听了这一事件的组件就可以在数据变化时得到通知。
??? Flex组件的属性大多可以用花括号“{}”进行绑定，也可以将一个组件的属性绑定到另一个组件的属性。同样用describeType进行分析，可以看到：
?
<
accessor?
name
="btn1"
?access
="readwrite"
?type
="mx.controls::Button"
?declaredBy
="FlexFramework"
>
????
<
metadata?
name
="Bindable"
>
??????
<
arg?
key
="event"
?value
="propertyChange"
/>
????
</
metadata
>
??
</
accessor
>
组件是通过监听propertyChange事件来更新数据的。但是前面的数据绑定声明并没有指定事件名称，这是因为[Bindable]是简化的写法，相当于[Bindable(event="propertyChange")]。这里的事件名称可以改变，但是Flex组件默认监听了名为propertyChange的事件，如果自己更改了事件名称，则必需在Flex中自己监听相应的事件并编写事件处理。
