Flex 3使用代码分离构建自定义组件

在创建组件时，MXML和ActionScript语言有不同的优点和缺点。
· 当你创建一个创建一个符合组件，MXML使得它容易被创建和安置子组件。
· 当你修改组件的行为，也就是说，覆盖他的方法，那么应该使用ActionScript。

大多数时间，当创建组件和应用时，同时使用MXML和ActionScript。Flex提供几种同时使用MXML和ActionScript的途径，包含如下：
· 在MXML标记中放置ActionScript代码声明，这使用于内联事件处理
· 在<mx:Script>标记中放置ActionScript代码。
· 使用<mx:Script>标记的source属性引入外部ActionScript文件。
· 使用MXML安置组件，把ActionScript代码放在一个类定义中。这种方式被叫做代码分离

要代码behind使用连接ActionScript和MXML，需要让ActionScript类作为MXML组件的更标记。也就是说，MXML组件扩展ActionScript类。
例如，要实现自定义AddressForm组件（显示符合地址登记表），你需要做如下事情：
1． 创建一个叫做AddressFormClass的ActionScript类。你可以使这个类扩展基本的Flex类。既然这样，使用Form容器的布局能力并且使AddressFormClass扩展mx.contain.form 类。
2． 创建一个命名为AddressForm的MXML组件，并且事他的更标记是AddressFormClass。
3． 使用MXML布局AddressForm组件的内容
4． 使用ActionScript来创建AddressForm组件的逻辑。

提示：你必须声明子组件为公共属性，在ActionScript类中

在下边的例子包含了自定义的AddressForm组件。主程序文件也利用了代码behind，并且这个例子也包含CountryCombox和PaddedPanel组件，这些在其他指导中创建的组件。
连接：在构建Flex应用程序时，这被认为是最佳实践架构的引论。更多的信息，查看Arp framework——一个开源的模式基础框架，用来创建Flash和Flex应用程序，他使用了代码分离。
数据模型
components/AddressVO.as

package components
{
public class AddressVO
{
// We are using public properties for the
// value object to keep this example short. In a

// real-world application, make these properties
// private and use implicit accessors to expose them
// so you can do validation, etc. if necessary.
public var name:String;
public var street:String;
public var city:String;
public var state:String;
public var country:String;
}

}
事件模型，定义事件类型和事件对应的数据
components/AddressFormEvent.as
package components
{
import flash.events.Event;
import components.AddressVO;

public class AddressFormEvent extends Event
{

public static const SUBMIT:String = "submit";

private var _data:AddressVO;

public function AddressFormEvent (eventName:String)

{
super (eventName);
}

public function set data (value:AddressVO):void

{
_data = value;
}

public function get data ():AddressVO
{

return _data;
}
}
}
定义视图的模型，处理事件
components/AddressFormClass.as
package components
{
import mx.events.FlexEvent;
import mx.controls.Button;
import mx.controls.TextInput;
import flash.events.MouseEvent;
import mx.containers.Form;

public class AddressFormClass extends Form
{
// Components in the MXML must be
// declared public. This is a limitation in
// the current version of Flex and may change
// in the future.
public var submitButton:Button;
public var nameInput:TextInput;
public var street:TextInput;
public var city:TextInput;
public var state:TextInput;
public var country:CountryComboBox;

// Constructor
public function AddressFormClass ():void
{
addEventListener(FlexEvent.CREATION_COMPLETE, creationCompleteHandler);
}

// Creation complete is a good time to add event listeners and
// interact with child components.
private function creationCompleteHandler (event:FlexEvent):void
{
submitButton.addEventListener(MouseEvent.CLICK, submitHandler);
}

// Gets called when the Submit button is clicked
private function submitHandler (event:MouseEvent):void
{
// Gather the data for this form
var addressVO:AddressVO = new AddressVO();
addressVO.name = nameInput.text;
addressVO.street = street.text;
addressVO.city = city.text;
addressVO.state = state.text;
addressVO.country = country.selectedItem as String;

var submitEvent:AddressFormEvent = new AddressFormEvent(AddressFormEvent.SUBMIT);
submitEvent.data = addressVO;

// Dispatch an event to signal that the form has been submitted
dispatchEvent(submitEvent);
}
}
}
视图的页面层，这里使用了上面的页面模型
components/AddressForm.mxml
<?xml version="1.0" encoding="utf-8"?>
<custom:AddressFormClass
xmlns:mx="http://www.adobe.com/2006/mxml"
xmlns:custom="components.*">
<mx:FormItem label="Name">
<mx:TextInput id="nameInput"/>
</mx:FormItem>
<mx:FormItem label="Street">
<mx:TextInput id="street"/>
</mx:FormItem>
<mx:FormItem label="City">
<mx:TextInput id="city"/>
</mx:FormItem>
<mx:FormItem label="State/County">
<mx:TextInput id="state"/>
</mx:FormItem>
<mx:FormItem label="Country">
<custom:CountryComboBox id="country"/>
</mx:FormItem>

<mx:Button
id="submitButton"
label="Submit"
/>
</custom:AddressFormClass>

应用层的模型：
components/ApplicationClass.as

package components
{
import mx.core.Application;
import mx.events.FlexEvent;
import mx.controls.Alert;

import components.AddressFormEvent;
import components.AddressVO;
import flash.utils.describeType;

public class ApplicationClass extends Application
{

// Components in MXML
public var addressForm:AddressForm;

public function ApplicationClass()

{
addEventListener (FlexEvent.CREATION_COMPLETE, creationCompleteHandler);
}

//
// Event handlers
//

private function creationCompleteHandler(event:FlexEvent):void
{

// The custom AddressForm component dispatches a "submit"
// event the form is submitted. Listen for this.
addressForm.addEventListener(AddressFormEvent.SUBMIT, submitHandler);
}

private function submitHandler(event:AddressFormEvent):void

{
// Get the value object (data) from the event object
var data:AddressVO = event.data as AddressVO;

// Compose a string to display the contents of the value object to the user.

var msg:String = "You submitted the following information: /r";

// Use the new introspection API and E4X to get a list of the properties
// in the data object and enumerate over them to compose the string.
var dataProperties:XMLList = describeType(data)..variable;

for each (var i:XML in dataProperties)
{

var propertyName:String = i.@name;
msg += i.@name + ": " + data[i.@name] + "/r";
}

// Display the contents of the address form to the user.
Alert.show(msg, "Thank you for submitting the form!");
}
}
应用层的视图
应用程序 MXML 文件
<?xml version="1.0" encoding="utf-8"?>
<custom:ApplicationClass
xmlns:custom="components.*"

viewSourceURL="src/CodeBehind/index.html"
width="400" height="310"
>
<custom:PaddedPanel title="Code Behind">

<custom:AddressForm id="addressForm"/>
</custom:PaddedPanel>
</custom:ApplicationClass>

消息流：
用户提交的数据—>被submitButton监听到，调用AddressFormClass中的sumbitHandler函数处理，封装的数据到AddressFormEvent中，并转发事件，被注册了AddressFormEvent的AddressForm监听到，调用ApplicationClass中的submitHandler进行处理。
这个完成了sumbitButton的事件到AddressForm的完美封装。
其中，sumbitButton的事件只负责收集页面的原始数据。而AddressForm的事件才是真正意义上这个自定义控件的事件。