Flex--读写本地文件 in Flash Player 10

     Flash Player 10中的一个新的特点就是更新了ActionScript FileReference APIs，新的FileReference允许Flash能够直接读写用户系统的数据。

     在Flash Player 10之前，为了能够读写用户的本地文件，Flash首先不得不先把它反弹回sever端，然后再从server端加载它，之后才可以访问它，这样不仅编程实现起来麻烦，而且还增加了应用的延迟和资源的使用。

     The new functionality is achieved through the addition of two new APIs on the FileReference class:

FileReference.load() : Loads data from a file selected by the user.
FileReference.save() : Saves data to a file location selected by the user.

需要记住以下几点：
  ·The load() and save() APIs can only be called in response to user interaction (such as a button click).
  ·The locations of the loaded and save files are not exposed to ActionScript.
  ·The APIs are asynchronous （异步的）(non-blocking).

 

Below are two examples that show how to use the APIs. The examples use Flex for the UI, but the ActionScript is the same regardless of whether you are using Flex or not.

 

Read a file from the users system: 

<?xml version="1.0" encoding="utf-8"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute"> <mx:Script> <!--[CDATA[ import flash.net.FileReference; import flash.net.FileFilter; import flash.events.IOErrorEvent; import flash.events.Event; import flash.utils.ByteArray; //FileReference Class well will use to load data private var fr:FileReference; //File types which we want the user to open private static const FILE_TYPES:Array = [new FileFilter("Text File", "*.txt;*.text")]; //called when the user clicks the load file button private function onLoadFileClick():void { //create the FileReference instance fr = new FileReference(); //listen for when they select a file fr.addEventListener(Event.SELECT, onFileSelect); //listen for when then cancel out of the browse dialog fr.addEventListener(Event.CANCEL,onCancel); //open a native browse dialog that filters for text files fr.browse(FILE_TYPES); } /************ Browse Event Handlers **************/ //called when the user selects a file from the browse dialog private function onFileSelect(e:Event):void { //listen for when the file has loaded fr.addEventListener(Event.COMPLETE, onLoadComplete); //listen for any errors reading the file fr.addEventListener(IOErrorEvent.IO_ERROR, onLoadError); //load the content of the file fr.load(); } //called when the user cancels out of the browser dialog private function onCancel(e:Event):void { trace("File Browse Canceled"); fr = null; } /************ Select Event Handlers **************/ //called when the file has completed loading private function onLoadComplete(e:Event):void { //get the data from the file as a ByteArray var data:ByteArray = fr.data; //read the bytes of the file as a string and put it in the //textarea outputField.text = data.readUTFBytes(data.bytesAvailable); //clean up the FileReference instance fr = null; } //called if an error occurs while loading the file contents private function onLoadError(e:IOErrorEvent):void { trace("Error loading file : " + e.text); } ]]--> </mx:Script> <mx:Button label="Load Text File" right="10" bottom="10" click="onLoadFileClick()"/> <mx:TextArea right="10" left="10" top="10" bottom="40" id="outputField"/> </mx:Application>  

Write a file to the users system:

<?xml version="1.0" encoding="utf-8"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute"> <mx:Script> <!--[CDATA[ import flash.net.FileReference; import flash.events.IOErrorEvent; import flash.events.Event; private static const DEFAULT_FILE_NAME:String = "example.txt"; //FileReference Class well will use to save data private var fr:FileReference; /********** UI Event Handlers **************/ //called when the users types in the textarea //note valueCommit should be used, but is broken in the flex build //I am using private function onInputChange():void { //enable button if there is any text to save saveButton.enabled = (inputField.text.length > 0); } //called when the user clicks the load file button private function onSaveClick():void { //create the FileReference instance fr = new FileReference(); //listen for the file has been saved fr.addEventListener(Event.COMPLETE, onFileSave); //listen for when then cancel out of the save dialog fr.addEventListener(Event.CANCEL,onCancel); //listen for any errors that occur while writing the file fr.addEventListener(IOErrorEvent.IO_ERROR, onSaveError); //open a native save file dialog, using the default file name fr.save(inputField.text, DEFAULT_FILE_NAME); } /***** File Save Event Handlers ******/ //called once the file has been saved private function onFileSave(e:Event):void { trace("File Saved"); fr = null; } //called if the user cancels out of the file save dialog private function onCancel(e:Event):void { trace("File save select canceled."); fr = null; } //called if an error occurs while saving the file private function onSaveError(e:IOErrorEvent):void { trace("Error Saving File : " + e.text); fr = null; } ]]--> </mx:Script> <mx:Button label="Save File" right="10" bottom="10" id="saveButton" click="onSaveClick()" enabled="false"/> <mx:TextArea right="10" left="10" top="36" bottom="40" id="inputField" editable="true" change="onInputChange()"/> <mx:Label text="Enter text to save" left="10" top="10" fontWeight="bold"/> </mx:Application>  

 

In addition to the events shown in the examples above, the following events are also broadcast by the APIS:

ProgressEvent.PROGRESS : Gives progress on the reading or writing of the file
Event.OPEN : Broadcast when the file is opened for reading or writing.
 While it will also be possible to use these APIs in Adobe AIR, in general, you will want to use the AIR File APIs as they provide more functionality and flexibility.