Actionscript 3: How to use describeType() to Save an Object to XML

Actionscript 3: How to use describeType() to Save an Object to XML

Submitted by ben.bishop
on Tue, 10/16/2007 - 00:33.

Actionscript 3

XML

Needed Resources:

Adobe Flex Builder 3 or Flex Builder 3 plug-in for Eclipse

Final Product:

A base data holder class that will have a toXMLString() method and a
parseXML() method to give its descendants the ability to generate a XML
string or to instantiate themselves with a XML string.

Execution:

After creating the class file

and constructor, create the toXMLString method:

public function toXMLString():String{

var x:XML = describeType(this);

var xl:XMLList = x..variable;

var xmlStr:String = "";

xmlStr ="<object type=/""+ getQualifiedClassName(this)

+"/">/r";

for each(var n:XML in xl){

xmlStr += "<variable name=/"" +

n.@name.toString() + "/" type=/"" + n.@type.toString() +

"/">";

xmlStr += this[n.@name.toString()].toString();

xmlStr += "</variable>/r";

}

xmlStr += "</object>";

return xmlStr;

}

This method first starts out by using the describeType utility function

to get a XML object that describes the object. Using e4x, a XMLList is

populated with variable nodes. After creating the root node, the method loops

through the XMLList and creates a series of new variable nodes that have the

actual variable value in addition to data type and variable name.

Next, create the

"parseXML" method:

public

function parseXML(s:String):void{

try{

var x:XML =

new XML(s);

var xl:XMLList = x..variable;

if(xl.length() == 0){

throw("DataObj

Error: XML does not contain any variable nodes.");

}else{

for each(var

n:XML in xl){

var

varNameStr:String = n.@name;

var varTypeStr:String = n.@type;

var varValueStr:String = n.toString();

if(hasOwnProperty(varNameStr) == true){

try{
this[varNameStr] = varValueStr;

}catch(e:Error){

switch(varTypeStr){

case "Array":

this[varNameStr] =

varValueStr.split(",");

break;

default:

throw("DataObj Error: Conversion of " +

varValueStr + " to " + varTypeStr + " failed for variable "

+ varNameStr + ". /r" + e.message);

break;

}

}

}else{
throw("DataObj Error: XML contains a variable

node that is not a class variable.");

}

}

}

}catch(e:Error){

throw(e.message);

}

}

This method starts off by attempting to parse the

passed string to XML. If there are any problems it throws an exception. Another

exception is thrown if the XMLList of variable nodes doesn't have any elements.

After extracting the variable name, type, and value, the class is tested to see

if it does indeed contain a property of that name. If all is well, the property

is assigned. An exception again will be thrown if there is a problem assigning

the property. In this example, the method does one last check to see if the

variable is an array. If so, appropriate action is taken.

A developer can now extend

off of this class and declare unique properties while retaining these

handy methods. For example:

package com.tw.model

{

public class Person extends DataObj

{

public var firstName:String;

public var lastName:String;

public var age:Number;

public var favoriteColors:Array = ["blue", "green",

"red"];

public function Person():void{

}

}

}

In this particular example, the simple data holder

class has been named "DataObj" and extended. A developer can do the

following:

var p:Person = new Person();

p.firstName = "Ben";

p.lastName = "Bishop";

p.age = 27;

When p.toXMLString() is invoked the following is

returned:

<object

type="com.tw.model::Person">

<variable name="lastName"

type="String">Bishop</variable>

<variable name="favoriteColors"

type="Array">blue,green,red</variable>

<variable name="age"

type="Number">27</variable>

<variable name="firstName"

type="String">Ben</variable>

</object>

Conversly, a developer can have another class

extend DataObj:

package com.tw.model

{

public class Car extends DataObj

{

//props

public var horsepower:Number;

public var numberOfCylinders:Number;

public var model:String;

public var features:Array;

//constructor

public function Car():void{

}

}

}

This object code be instantiated with the following

code:

var c:Car = new Car();

var xmlStr:String = "<object

type=/"com.tw.model::Car/">";

xmlStr += "<variable name=/"model/"

type=/"String/">";

xmlStr += "Honda Civic";

xmlStr += "</variable>";

xmlStr += "<variable name=/"numberOfCylinders/"

type=/"Number/">";

xmlStr += "4";

xmlStr += "</variable>";

xmlStr += "<variable name=/"features/"

type=/"Array/">";

xmlStr += "power windows, power locks, ABS";

xmlStr += "</variable>";

xmlStr += "</object>";

c.parseXML(xmlStr);

Pretty neat, eh?

What this cold be used for:

Saving program states to the

hard drive via AIR for later retrieval. An example of reading and writing

XML files can be found here
.

A quick way to save an object

to a database through a webservice for later use.

A method to save data to an

AIR SQLLite DB.

Source code for this example can be found attached to this post. Comments

about how to improve and make this more useful is STRONGLY encouraged!
http://tdotblog.info/?q=node/11