Asynchronous programming and the events generated by a FileStream object opened asynchronously

Adobe AIR 1.0 and later

When a file is opened asynchronously (using the openAsync() method), reading and writing files are done asynchronously. As data is read into the read buffer and as output data is being written, other ActionScript code can execute.

This means that you need to register for events generated by the FileStream object opened asynchronously.

By registering for the progress event, you can be notified as new data becomes available for reading, as in the following code: 

var myFile:File = File.documentsDirectory.resolvePath("AIR Test/test.txt"); 
var myFileStream:FileStream = new FileStream(); 
myFileStream.addEventListener(ProgressEvent.PROGRESS, progressHandler); 
myFileStream.openAsync(myFile, FileMode.READ); 
var str:String = ""; 
 
function progressHandler(event:ProgressEvent):void  
{ 
    str += myFileStream.readMultiByte(myFileStream.bytesAvailable, "iso-8859-1"); 
}

You can read the entire data by registering for the complete event, as in the following code: 

var myFile:File = File.documentsDirectory.resolvePath("AIR Test/test.txt"); 
var myFileStream:FileStream = new FileStream(); 
myFileStream.addEventListener(Event.COMPLETE, completed); 
myFileStream.openAsync(myFile, FileMode.READ); 
var str:String = ""; 
function completeHandler(event:Event):void  
{ 
    str = myFileStream.readMultiByte(myFileStream.bytesAvailable, "iso-8859-1"); 
}

In much the same way that input data is buffered to enable asynchronous reading, data that you write on an asynchronous stream is buffered and written to the file asynchronously. As data is written to a file, the FileStream object periodically dispatches an OutputProgressEvent object. An OutputProgressEvent object includes a bytesPending property that is set to the number of bytes remaining to be written. You can register for the outputProgress event to be notified as this buffer is actually written to the file, perhaps in order to display a progress dialog. However, in general, it is not necessary to do so. In particular, you may call the close() method without concern for the unwritten bytes. The FileStream object will continue writing data and the close event will be delivered after the final byte is written to the file and the underlying file is closed.