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Part 1 of this series gave examples of how to work with directories within the file system. Part 2 of this series gave examples of how to work the File and FileStream classes to work within the file system. This excerpt covers the differences between asynchronous and synchronous calls to the File classes methods. It will also show how to create temporary directories and files.
Asynchronous versus Synchronous
The examples given so far have concentrated on synchronous methods. Calling a method synchronously means that while the call is being made the application pauses until the method call has completed. For example, let's say that you would like to read in file information for 1,000 images that exist in an image folder. Doing this as a synchronous method would mean that the application would be unusable while it is reading in the image files. A better way to do this would be to use an asynchronous method, which would allow the user to continue to use the application while the asynchronous method executes. While the asynchronous method is executing, you can receive updates of its progress by setting up event listeners.
There are asynchronous versions of many of the File class methods. Here is the complete list:
Directories
copyToAsync()
deleteDirectoryAsync()
getDirectoryListingAsync()
moveToAsync()
moveToTrashAsync()
Files
copyToAsync()
deleteFileAsync()
moveToAsync()
moveToTrashAsync()
FileStream
openAsync()
The following examples will demonstrate how to use the deleteDirectoryAsync() method of the File class as well as the openAsync() method of the FileStream class. The same principles can be used for all of the other asynchronous methods as well.
To test the example in Listing 8-6, create a directory first by clicking on the Create Directory button, and then delete the directory asynchronously by clicking on the Delete Directory button. The results can be seen in Figure 8-6.
<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml"
layout="absolute">
<mx:Script>
<![CDATA[
import flash.filesystem.File;
import mx.events.FileEvent;
import mx.controls.Alert;
/*
Create a new directory
*/
private function createDirectory():void{
var newDirectory:File=File.desktopDirectory.resolvePath("MyNewDirectory");
newDirectory.createDirectory();
}
/*
Delete directory Asynchronously
*/
private function deleteDirectory():void{
var directory:File = File.desktopDirectory.resolvePath("MyNewDirectory");
directory.addEventListener(Event.COMPLETE,completeHandler);
directory.deleteDirectoryAsync();
}
private function completeHandler(event:Event):void {
Alert.show("Directory deleted","Complete Handler");
}
]]>
</mx:Script>
<mx:Button label="Create Directory"
click="createDirectory()" y="10" horizontalCenter="0"/>
<mx:Button label="Delete Directory"
click="deleteDirectory()" y="40" horizontalCenter="0"/>
</mx:WindowedApplication>
Figure 8-6: The complete handler triggered when Delete event is completed.
The example in Listing 8-7 demonstrates how to use the openAsynch method of the FileStream class. To test this, create a file by clicking on the Create File button, and then read the file asynchronously by clicking on the Read File Asynchronously button. The results can be seen in Figure 8-7.
<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml"
layout="absolute">
<mx:Script>
<![CDATA[
import mx.controls.Alert;
import mx.events.FileEvent;
import flash.filesystem.FileMode;
import flash.filesystem.FileStream;
import flash.filesystem.File;
private var fileContents:String;
/*
Create a new file
*/
private function createFile():void{
var newFile:File = File.desktopDirectory.resolvePath("MyNewFile.txt");
var fileStream:FileStream = new FileStream();
fileStream.open(newFile, FileMode.WRITE);
fileStream.writeUTFBytes("Beginning AIR by Rich Tretola");
fileStream.close();
}
/*
Read in a file
Note: Be sure to create the file first
*/
private function readFileAsynch():void{
var resourceFile:File = File.desktopDirectory.resolvePath("MyNewFile.txt");
var fileStream:FileStream = new FileStream();
fileStream.openAsync(resourceFile, FileMode.READ);
fileStream.addEventListener(Event.CLOSE,completeHandler);
fileStream.addEventListener(IOErrorEvent.IO_ERROR,errorHandler);
fileContents = fileStream.readUTFBytes(fileStream.bytesAvailable);
fileStream.close();
}
private function completeHandler(event:Event):void {
Alert.show("File read completed","Complete Handler");
}
private function errorHandler(event:IOErrorEvent):void {
Alert.show("Error " + event.text,"errorHandler");
}
]]>
</mx:Script>
<mx:Button label="Create File"
click="createFile()" y="10" horizontalCenter="0"/>
<mx:Button label="Read File Asynchronously"
click="readFileAsynch()" y="40" horizontalCenter="0"/>
</mx:WindowedApplication>
Figure 8-7: The complete handler triggered when File Read is completed.
Creating Temporary Files and Directories
There may be occasions when you would like to have local file storage for temporary files and directories. AIR has included methods within the File API to create temporary directories and files. After importing the File class, a temporary (temp) directory can be created by calling the createTempDirectory() method on the File class, and a temp file can be created by calling the createTempFile() method.
Listing 8-8 shows how to create a temporary directory and a temp file.
<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml"
layout="absolute">
<mx:Script>
<![CDATA[
import mx.controls.Alert;
import flash.filesystem.File;
private function createTempDirectory():void{
var tempDirectory:File = File.createTempDirectory();
Alert.show("nativePath = " + tempDirectory.nativePath +
"\n\nisDirectory = " + tempDirectory.isDirectory,
"tempDirectory");
}
private function createTempFile():void{
var tempFile:File = File.createTempFile();
Alert.show("nativePath = " + tempFile.nativePath +
"\n\nisDirectory = " + tempFile.isDirectory,
"tempFile");
}
]]>
</mx:Script>
<mx:Button label="Create Temp Directory"
click="createTempDirectory()" horizontalCenter="0"
y="10"/>
<mx:Button label="Create Temp File"
click="createTempFile()" horizontalCenter="0"
y="40"/>
</mx:WindowedApplication>
The results can be see in Figures 8-8 and 8-9. Notice that the output of the isDirectory property in each figure shows that the temp directory is recognized as a directory, while the temp file is not. If you are running this sample on a Windows machine, your expected outcome would be a file path similar to C:\Documents and Settings\rich\Local Settings\Temp\fla28F.tmp.
Figure 8-8: The nativePath and isDirectory property
of a temp directory created on Mac OS X.
Figure 8-9: The nativePath and isDirectory properties
of a temp file created on Mac OS X.
To read the rest of this chapter, which includes the browse for files dialog, and read the rest of the book please order a copy at Amazon.com. The 1st 2 people to email me proof that they have the book in hand can get a free copy of Professional Flex 2. See this post at EverythingFlex.com for details.
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Bought your book a couple of months ago. A great place to start learning AIR. Well reccomended to beginners. If you already have some Flex understanding, it might be a bit over-simplistic but a great reference for examples using the AIR classes. Like the above example, clear coding, and to the point. Thanks for all your hard work.
Thanks Jed,
I would also recommend the new AIR cookbook :-)
http://www.amazon.com/Adobe-AIR-Cookbook-Application-Developers/dp/0596522509
How we can create file at user specific path?
var file:File=File.userDirectory.resolvePath(”c:\Data\Hello.txt”);.
I got this error “Error #3003: File or directory does not exist.”