flex4 -- fx:Vector 使用

原文：http://opensource.adobe.com/wiki/display/flexsdk/MXML+Vector+Support

Summary and Background

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The purpose of this feature is to support the ActionScript Vector type in MXML for the Gumbo release of the Flex SDK.

Vectors are similar to Arrays but their contents are restricted to a single base type. This makes Vector operations faster than those on an Array and provides type safety.

Usage Scenarios

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A component defines a property to be of type "Vector.<String>" and Finn initializes it via MXML.

Detailed Description

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This feature will mirror MXML's Array support with the addition of allowing the Vector's data type to be specified as a tag attribute and exposing Vector's "fixed" property as an attribute. For example:

<fx:Vector id="myVector" type="String" fixed="true">
  <fx:String>hi</fx:String>
  <fx:String>bye</fx:String>
</fx:Vector>

As with ActionScript,the value of Vector's fixed attribute is false by default.

It's worth noting that MXML Array support has some interesting functionality. For example,if the property being initialized is of type Array,the compiler will implicitly coerce a list of children by wrapping them in a new Array. If the list of children is a singleton,the compiler will only wrap the child if it's not already an Array.

For Vectors,the compiler will also implicitly coerce a list of children by wrapping them in a new Vector. For singletons,the compiler will wrap the child if it's not already a Vector. If it's a Vector with the wrong data type,an error will be reported. See the Examples and Usage section below.

The compiler will not support initializing properties of type Array with a Vector and it will not support initializing properties of type Vector with an Array. This is consistent with ActionScript Vector support.

The generated code for a Vector initialization currently looks like the following:

private function _foo_Vector1_c() : __AS3__.vec.Vector.<String> { var temp : __AS3__.vec.Vector.<String> = new <String>["hi","bye"]; myVector2 = temp; return temp; }

In order to allow older applications to take advantage of the increased performance of using Vector,Vector will be allowed in the MXML 2006 and 2009 namespaces.

API Description

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The "type" tag attribute is required and must be the fully qualified,using dot Syntax,class name of the Vector's data type. The boolean "fixed" tag attribute is optional and false by default.

nested Vectors

A case worth mentioning is nested Vectors. The type attribute of an outer Vector must declare the type of the inner Vector by escaping the < and > Syntax with &lt; and &gt; in order to maintain a valid XML document.

"Vector.&lt;String&gt;" fixed=true"> <fx:Vector type=String"> <fx:String>one</fx:String> <fx:String>two</fx:String> </fx:Vector> <fx:Vector type=String>A</fx:String>B</fx:String> </fx:Vector> </fx:Vector>