[转] <What can you do with bytes ?> 第二章 第一节: 对象的复制
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来源页面: http://www.bytearray.org/wp-content/projects/wcydwb/Chapter%202%20-%20Everyday%20bytes.pdf
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资讯原作者: Thibault Imbert
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本帖最后由 sun11086 于 2011-3-15 17:14 编辑
第一节
复制对象
复制对象是ByteArray最常用的用途之一.我们可以通过Bytearray的API对AMF进行序列化和反序列化.writeObject就是我们需要的API:
// creates an empty ByteArray var stream:ByteArray = new ByteArray(); // creates an object var parameters:Object = { age : 25, name : "Bob" }; // serializes the object as amf and stores it into the ByteArray stream.writeObject( parameters );
我们通过API readObject来提取已序列化的实例:
// creates an empty ByteArray var stream:ByteArray = new ByteArray(); // creates an object What can you do with bytes ? – Chapter 2 – Everyday bytes var parameters:Object = { age : 25, name : "Bob" }; // serializes the object as amf and stores it into the ByteArray stream.writeObject( parameters ); // resets the position stream.position = 0; // reads the object copy var objectCopy:Object = stream.readObject();
然后我们可以将下面的逻辑放到一个自定义函数中:
function copyObject ( objectToCopy:* ):*{ var stream:ByteArray = new ByteArray(); stream.writeObject( objectToCopy ); stream.position = 0; return stream.readObject(); }
在任何需要的时候,我们可以通过调用copyObject函数来复制对象:
// creates an object var parameters:Object = { age : 25, name : "Bob" }; var parametersCopy:Object = copyObject ( parameters ); /* outputs : name :Bob age:25 */ for ( var p:String in parametersCopy ) trace( p, " : ", parametersCopy ); function copyObject ( objectToCopy:* ):*{ var stream:ByteArray = new ByteArray(); stream.writeObject( objectToCopy ); stream.position = 0; return stream.readObject(); }
通过修改原始对象的属性,我们可以看到我们已经正确的复制了对象的所有属性:
// creates an object var parameters:Object = { age : 25, name : "Bob" }; var parametersCopy:Object = copyObject ( parameters ); parameters.nom = "Stevie"; /* outputs : name :Bob age:25 */ for ( var p:String in parametersCopy ) trace( p, " : ", parametersCopy ); function copyObject ( objectToCopy:* ):*{ What can you do with bytes ? – Chapter 2 – Everyday bytes var stream:ByteArray = new ByteArray(); stream.writeObject( objectToCopy ); stream.position = 0; return stream.readObject(); }
让我们进一步探寻怎么样通过ByteArray的API实现更多复杂类型的存储和提取.
序列化/反序列化 自定义对象
需要注意的是下段代码对自定义类型不起作用.用一个简单的例子来说明:现在你需要使用到如下的一个User对象.
package{ public class User { private var _firstName:String; private var _lastName:String; public function set firstName (firstName:String):void { _firstName = firstName; } public function set lastName (lastName:String):void { _lastName = lastName; } public function get firstName ():String { return _firstName; } public function get lastName ():String { return _lastName; } } }
也许你需要将User实例存以二进制形式存储到服务器或者存储到本地的SharedObject中.如果你尝试将User的实例存储到ByteArray中并且以后会再次提取它,当读取它的时候,Flash Player将会在内部检索是否已经注册过名为User的类型,如果没有player就会按照Object的类型来反序列法该对象:
// creates an instance of User var myUser:User = new User (); // sets the members myUser.firstName = "Stevie"; myUser.lastName = "Wonder"; // outputs : trace ( myUser ); // create a ByteArray to store the instance var bytes:ByteArray = new ByteArray(); // stores the instance What can you do with bytes ? – Chapter 2 – Everyday bytes bytes.writeObject ( myUser ); // resets the position bytes.position = 0; // outputs : false trace ( bytes.readObject() is User );
现在,我们通过使用registerClassAlias来告知Flash player并注册User类型,以便Flash Player来自动反序列化User类型的实例.
// creates an instance of User var myUser:User = new User (); // sets the members myUser.firstName = "Stevie"; myUser.lastName = "Wonder"; // outputs : trace ( myUser ); // registers the type User for deserialization registerClassAlias ( "userTypeAlias", User ); // create a ByteArray to store the instance var bytes:ByteArray = new ByteArray(); // stores the instance bytes.writeObject ( myUser ); // resets the position bytes.position = 0; // reads the stored instance and automatically deserializes it to the User type var storedUser:User = bytes.readObject() as User; // outputs : true trace ( storedUser is User ); // outputs : Stevie Wonder trace ( storedUser.firstName, storedUser.lastName );
通过这种技术我们可以保存任何自定类型的对象 并且 提取他们.正如你看到的我们将复制一个自定义类型:
storedUser.firstName = "Bobby"; storedUser.lastName = "Womack"; // outputs : Stevie Wonder trace ( myUser.firstName, myUser.lastName ); // outputs : Bobby Womack trace ( storedUser.firstName, storedUser.lastName );
需要注意的是一些基础类型是不能被序列化或反序列化为AMF.例如DisplayObject等.所以如果你想将一个MovieClip的实例序列化是行不通的:
// creates a ByteArray var bytes:ByteArray = new ByteArray(); // try storing a DisplayObject type bytes.writeObject ( new MovieClip() ); // resets the position bytes.position = 0; What can you do with bytes ? – Chapter 2 – Everyday bytes // outputs : undefined trace ( bytes.readObject() );
AMF3对显示对象的支持将会是一个非常大的补充.
英文词汇:4780(不计空格)
翻译后词汇:3917(不计空格)
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