读写本地文件 in Flash Player 10

     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: 

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1. <?xml version="1.0" encoding="utf-8"?>  


2. <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">  


3.   


4.     <mx:Script>  


5.         <!--[CDATA[  


6.             import flash.net.FileReference;  


7.             import flash.net.FileFilter;  


8.   


9.             import flash.events.IOErrorEvent;  


10.             import flash.events.Event;  


11.   


12.             import flash.utils.ByteArray;  


13.   


14.             //FileReference Class well will use to load data  


15.             private var fr:FileReference;  


16.   


17.             //File types which we want the user to open  


18.             private static const FILE_TYPES:Array = [new FileFilter("Text File", "*.txt;*.text")];  


19.   


20.             //called when the user clicks the load file button  


21.             private function onLoadFileClick():void  


22.             {  


23.                 //create the FileReference instance  


24.                 fr = new FileReference();  


25.   


26.                 //listen for when they select a file  


27.                 fr.addEventListener(Event.SELECT, onFileSelect);  


28.   


29.                 //listen for when then cancel out of the browse dialog  


30.                 fr.addEventListener(Event.CANCEL,onCancel);  


31.   


32.                 //open a native browse dialog that filters for text files  


33.                 fr.browse(FILE_TYPES);  


34.             }  


35.   


36.             /************ Browse Event Handlers **************/  


37.   


38.             //called when the user selects a file from the browse dialog  


39.             private function onFileSelect(e:Event):void  


40.             {  


41.                 //listen for when the file has loaded  


42.                 fr.addEventListener(Event.COMPLETE, onLoadComplete);  


43.   


44.                 //listen for any errors reading the file  


45.                 fr.addEventListener(IOErrorEvent.IO_ERROR, onLoadError);  


46.   


47.                 //load the content of the file  


48.                 fr.load();  


49.             }  


50.   


51.             //called when the user cancels out of the browser dialog  


52.             private function onCancel(e:Event):void  


53.             {  


54.                 trace("File Browse Canceled");  


55.                 fr = null;  


56.             }  


57.   


58.             /************ Select Event Handlers **************/  


59.   


60.             //called when the file has completed loading  


61.             private function onLoadComplete(e:Event):void  


62.             {  


63.                 //get the data from the file as a ByteArray  


64.                 var data:ByteArray = fr.data;  


65.   


66.                 //read the bytes of the file as a string and put it in the  


67.                 //textarea  


68.                 outputField.text = data.readUTFBytes(data.bytesAvailable);  


69.   


70.                 //clean up the FileReference instance  


71.   


72.                 fr = null;  


73.             }  


74.   


75.             //called if an error occurs while loading the file contents  


76.             private function onLoadError(e:IOErrorEvent):void  


77.             {  


78.                 trace("Error loading file : " + e.text);  


79.             }  


80.   


81.         ]]-->  


82.     </mx:Script>  


83.   


84.     <mx:Button label="Load Text File" right="10" bottom="10" click="onLoadFileClick()"/>  


85.     <mx:TextArea right="10" left="10" top="10" bottom="40" id="outputField"/>  


86.   


87. </mx:Application>  

 

Write a file to the users system:

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1. <?xml version="1.0" encoding="utf-8"?>  


2. <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">  


3.   


4.     <mx:Script>  


5.         <!--[CDATA[  


6.   


7.             import flash.net.FileReference;  


8.   


9.             import flash.events.IOErrorEvent;  


10.             import flash.events.Event;  


11.   


12.             private static const DEFAULT_FILE_NAME:String = "example.txt";  


13.   


14.             //FileReference Class well will use to save data  


15.             private var fr:FileReference;  


16.   


17.             /********** UI Event Handlers **************/  


18.   


19.             //called when the users types in the textarea  


20.             //note valueCommit should be used, but is broken in the flex build   


21.             //I am using  


22.             private function onInputChange():void  


23.             {  


24.                 //enable button if there is any text to save  


25.                 saveButton.enabled = (inputField.text.length > 0);  


26.             }  


27.   


28.             //called when the user clicks the load file button  


29.             private function onSaveClick():void  


30.             {  


31.                 //create the FileReference instance  


32.                 fr = new FileReference();  


33.   


34.                 //listen for the file has been saved  


35.                 fr.addEventListener(Event.COMPLETE, onFileSave);  


36.   


37.                 //listen for when then cancel out of the save dialog  


38.                 fr.addEventListener(Event.CANCEL,onCancel);  


39.   


40.                 //listen for any errors that occur while writing the file  


41.                 fr.addEventListener(IOErrorEvent.IO_ERROR, onSaveError);  


42.   


43.                 //open a native save file dialog, using the default file name  


44.                 fr.save(inputField.text, DEFAULT_FILE_NAME);  


45.             }  


46.   


47.             /***** File Save Event Handlers ******/  


48.   


49.             //called once the file has been saved  


50.             private function onFileSave(e:Event):void  


51.             {  


52.                 trace("File Saved");  


53.                 fr = null;  


54.             }  


55.   


56.             //called if the user cancels out of the file save dialog  


57.             private function onCancel(e:Event):void  


58.             {  


59.                 trace("File save select canceled.");  


60.                 fr = null;  


61.             }  


62.   


63.             //called if an error occurs while saving the file  


64.             private function onSaveError(e:IOErrorEvent):void  


65.             {  


66.                 trace("Error Saving File : " + e.text);  


67.                 fr = null;  


68.             }  


69.         ]]-->  


70.     </mx:Script>  


71.   


72.     <mx:Button label="Save File" right="10" bottom="10" id="saveButton"  


73.                                             click="onSaveClick()" enabled="false"/>  


74.     <mx:TextArea right="10" left="10" top="36" bottom="40" id="inputField"  


75.                                     editable="true" change="onInputChange()"/>  


76.     <mx:Label text="Enter text to save" left="10" top="10" fontWeight="bold"/>  


77.   


78. </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.