A
File object is a pointer to a file or directory in the file system.
The File class extends the FileReference class. The FileReference
class, which is available in Adobe® Flash® Player as well as AIR, represents a pointer
to a file. The File class adds properties and methods that are not
exposed in Flash Player (in a SWF file running in a browser), due
to security considerations.
About the File class
You can use the File class for the following:
-
Getting the path to special directories, including the
user directory, the user's documents directory, the directory from
which the application was launched, and the application directory
-
Coping files and directories
-
Moving files and directories
-
Deleting files and directories (or moving them to the trash)
-
Listing files and directories contained in a directory
-
Creating temporary files and folders
Once a File object points to a file path, you can use it to read
and write file data, using the FileStream class.
A File object can point to the path of a file or directory that
does not yet exist. You can use such a File object in creating a
file or directory.
Paths of File objects
Each File object has two properties that each define its path:
Property
|
Description
|
nativePath
|
Specifies the platform-specific path to
a file. For example, on Windows a path might be "c:\Sample directory\test.txt"
whereas on Mac OS it could be "/Sample directory/test.txt". A
nativePath
property
uses the backslash (\) character as the directory separator character
on Windows, and it uses the forward slash (/) character on Mac OS
and Linux.
|
url
|
This may use the file URL scheme to point
to a file. For example, on Windows a path might be "file:///c:/Sample%20directory/test.txt"
whereas on Mac OS it could be "file:///Sample%20directory/test.txt".
The runtime includes other special URL schemes besides
file
and
are described in
Supported AIR URL schemes
|
The File class includes static properties for pointing to standard
directories on Mac OS, Windows, and Linux. These properties include:
-
File.applicationStorageDirectory
—a
storage directory unique to each installed AIR application. This
directory is an appropriate place to store dynamic application assets
and user preferences. Consider storing large amounts of data elsewhere.
-
File.applicationDirectory
—the directory
where the application is installed (along with any installed assets).
On some operating systems, the application is stored in a single
package file rather than a physical directory. In this case, the
contents may not be accessible using the native path. The application
directory is read-only.
-
File.desktopDirectory
—the user’s desktop
directory. If a platform does not define a desktop directory, another
location on the file system is used.
-
File.documentsDirectory
—the user’s documents
directory. If a platform does not define a documents directory,
another location on the file system is used.
-
File.userDirectory
—the user directory. If
a platform does not define a user directory, another location on
the file system is used.
Note:
When a platform does not define standard locations for desktop,
documents, or user directories,
File.documentsDirectory
,
File.desktopDirectory
,
and
File.userDirectory
can reference the same directory.
These properties have different values on different operating
systems. For example, Mac and Windows each have a different native
path to the user’s desktop directory. However, the
File.desktopDirectory
property
points to an appropriate directory path on every platform. To write
applications that work well across platforms, use these properties
as the basis for referencing other directories and files used by
the application. Then use the
resolvePath()
method
to refine the path. For example, this code points to the preferences.xml file
in the application storage directory:
var prefsFile:File = air.File.applicationStorageDirectory;
prefsFile = prefsFile.resolvePath("preferences.xml");
Although the File class lets you point to a specific file path,
doing so can lead to applications that do not work across platforms.
For example, the path C:\Documents and Settings\joe\ only works
on Windows. For these reasons, it is best to use the static properties
of the File class, such as
File.documentsDirectory
.
Common directory locations
Platform
|
Directory type
|
Typical file system location
|
Linux
|
Application
|
/opt/filename/share
|
Application-storage
|
/home/userName/.appdata/applicationID/Local Store
|
Desktop
|
/home/userName/Desktop
|
Documents
|
/home/userName/Documents
|
Temporary
|
/tmp/FlashTmp.randomString
|
User
|
/home/userName
|
Mac
|
Application
|
/Applications/filename.app/Contents/Resources
|
Application-storage
|
/Users/userName/Library/Preferences/applicationID/Local Store
|
Desktop
|
/Users/userName/Desktop
|
Documents
|
/Users/userName/Documents
|
Temporary
|
/private/var/folders/JY/randomString/TemporaryItems/FlashTmp
|
User
|
/Users/userName
|
Windows
|
Application
|
C:\Program Files\filename
|
Application-storage
|
C:\Documents and settings\userName\ApplicationData\applicationID\Local Store
|
Desktop
|
C:\Documents and settings\userName\Desktop
|
Documents
|
C:\Documents and settings\userName\My Documents
|
Temporary
|
C:\Documents and settings\userName\Local Settings\Temp\randomString.tmp
|
User
|
C:\Documents and settings\userName
|
The actual native paths for these directories vary based on the
operating system and computer configuration. The paths shown in
this table are typical examples. You should always use the appropriate
static File class properties to refer to these directories so that
your application works correctly on any platform. In an actual AIR
application, the values for
applicationID
and
filename
shown
in the table are taken from the application descriptor. If you specify
a publisher ID in the application descriptor, then the publisher
ID is appended to the application ID in these paths. The value for
userName
is
the account name of the installing user.
Pointing a File object to a directory
There
are different ways to set a File object to point to a directory.
Pointing to the user’s home directory
You can point a File object to the user’s home directory. The
following code sets a File object to point to an AIR Test subdirectory
of the home directory:
var file = air.File.userDirectory.resolvePath("AIR Test");
Pointing to the user’s documents directory
You can point a File object to the user's documents directory.
The following code sets a File object to point to an AIR Test subdirectory
of the documents directory:
var file = air.File.documentsDirectory.resolvePath("AIR Test");
Pointing to the desktop directory
You can point a File object to the desktop. The following code
sets a File object to point to an AIR Test subdirectory of the desktop:
var file = air.File.desktopDirectory.resolvePath("AIR Test");
Pointing to the application storage directory
You can point a File object to the application storage directory.
For every AIR application, there is a unique associated path that
defines the application storage directory. This directory is unique
to each application and user. You can use this directory to store
user-specific, application-specific data (such as user data or preferences
files). For example, the following code points a File object to a
preferences file, prefs.xml, contained in the application storage
directory:
var file = air.File.applicationStorageDirectory;
file = file.resolvePath("prefs.xml");
The application storage directory location is typically based
on the user name and the application ID. The following file system
locations are given here to help you debug your application. You
should always use the
File.applicationStorage
property
or
app-storage:
URI scheme to resolve files in
this directory:
-
On Mac OS—In:
/Users/
user name
/Library/Preferences/
applicationID
/Local Store/
For
example:
/Users/babbage/Library/Preferences/com.example.TestApp/Local Store
-
On Windows—In the documents and Settings directory, in:
C:\Documents and Settings\user name
\Application Data\
applicationID
\Local Store\
For
example:
C:\Documents and Settings\babbage\Application Data\com.example.TestApp\Local Store
-
On Linux—In:
/home/
user name
/.appdata/
applicationID
/Local Store/
For
example:
/home/babbage/.appdata/com.example.TestApp/Local Store
Note:
If an application has a publisher ID, then the publisher ID
is also used as part of the path to the application storage directory.
The URL (and
url
property) for a File object
created with
File.applicationStorageDirectory
uses
the
app-storage
URL scheme (see
Supported AIR URL schemes
), as in the following:
var dir = air.File.applicationStorageDirectory;
dir = dir.resolvePath("prefs.xml");
air.trace(dir.url); // app-storage:/preferences
Pointing to the application directory
You can point a File object to the directory in which the application
was installed, known as the application directory. You can reference
this directory using the
File.applicationDirectory
property.
You can use this directory to examine the application descriptor
file or other resources installed with the application. For example,
the following code points a File object to a directory named
images
in
the application directory:
var dir = air.File.applicationDirectory;
dir = dir.resolvePath("images");
The URL (and
url
property) for a File object
created with
File.applicationDirectory
uses the
app
URL
scheme (see
Supported AIR URL schemes
), as in the following:
var dir = air.File.applicationDirectory;
dir = dir.resolvePath("images");
air.trace(dir.url); // app:/images
Pointing to the file system root
The
File.getRootDirectories()
method lists all
root volumes, such as C: and mounted volumes, on a Windows computer.
On Mac OS and Linux, this method always returns the unique root
directory for the machine (the "/" directory). The
StorageVolumeInfo.getStorageVolumes()
method provides
more detailed information on mounted storage volumes (see
Working with storage volumes
).
Pointing to an explicit directory
You can point the File object to an explicit directory by setting
the
nativePath
property of the File object, as
in the following example (on Windows):
var file = new air.File();
file.nativePath = "C:\\AIR Test";
Important:
Pointing to an explicit path this way can lead
to code that does not work across platforms. For example, the previous
example only works on Windows. You can use the static properties
of the File object, such as
File.applicationStorageDirectory
,
to locate a directory that works cross-platform. Then use the
resolvePath()
method
(see the next section) to navigate to a relative path.
Navigating to relative paths
You can use the
resolvePath()
method to obtain
a path relative to another given path. For example, the following
code sets a File object to point to an "AIR Test" subdirectory of
the user's home directory:
var file = air.File.userDirectory;
file = file.resolvePath("AIR Test");
You can also use the
url
property of a File
object to point it to a directory based on a URL string, as in the
following:
var urlStr = "file:///C:/AIR Test/";
var file = new air.File()
file.url = urlStr;
For more information, see
Modifying File paths
.
Letting the user browse to select a directory
The File class includes the
browseForDirectory()
method,
which presents a system dialog box in which the user can select
a directory to assign to the object. The
browseForDirectory()
method
is asynchronous. The File object dispatches a
select
event
if the user selects a directory and clicks the Open button, or it
dispatches a
cancel
event if the user clicks the
Cancel button.
For example, the following code lets the user select a directory
and outputs the directory path upon selection:
var file = new air.File();
file.addEventListener(air.Event.SELECT, dirSelected);
file.browseForDirectory("Select a directory");
function dirSelected(event) {
alert(file.nativePath);
}
Pointing to the directory from which the application was invoked
You can get the directory location from which an application
is invoked, by checking the
currentDirectory
property
of the InvokeEvent object dispatched when the application is invoked.
For details, see
Capturing command line arguments
.
Pointing a File object to a file
There are different
ways to set the file to which a File object points.
Pointing to an explicit file path
Important:
Pointing to an explicit path can lead to code
that does not work across platforms. For example, the path C:/foo.txt
only works on Windows. You can use the static properties of the
File object, such as
File.applicationStorageDirectory
,
to locate a directory that works cross-platform. Then use the
resolvePath()
method
(see
Modifying File paths
) to navigate to a relative path.
You can use the
url
property of a File object
to point it to a file or directory based on a URL string, as in
the following:
var urlStr = "file:///C:/AIR Test/test.txt";
var file = new air.File()
file.url = urlStr;
You can also pass the URL to the
File()
constructor
function, as in the following:
var urlStr = "file:///C:/AIR Test/test.txt";
var file = new air.File(urlStr);
The
url
property always returns the URI-encoded
version of the URL (for example, blank spaces are replaced with
"%20
):
file.url = "file:///c:/AIR Test";
alert(file.url); // file:///c:/AIR%20Test
You can also use the
nativePath
property of
a File object to set an explicit path. For example, the following
code, when run on a Windows computer, sets a File object to the
test.txt file in the AIR Test subdirectory of the C: drive:
var file = new air.File();
file.nativePath = "C:/AIR Test/test.txt";
You can also pass this path to the
File()
constructor
function, as in the following:
var file = new air.File("C:/AIR Test/test.txt");
Use
the forward slash (/) character as the path delimiter for the
nativePath
property.
On Windows, you can also use the backslash (\) character, but doing
so leads to applications that do not work across platforms.
For more information, see
Modifying File paths
.
Enumerating files in a directory
You can use the
getDirectoryListing()
method
of a File object to get an array of File objects pointing to files
and subdirectories at the root level of a directory. For more information,
see
Enumerating directories
.
Letting the user browse to select a file
The
File class includes the following methods that present a system
dialog box in which the user can select a file to assign to the
object:
-
browseForOpen()
-
browseForSave()
-
browseForOpenMultiple()
These methods are each asynchronous. The
browseForOpen()
and
browseForSave()
methods
dispatch the select event when the user selects a file (or a target
path, in the case of browseForSave()). With the
browseForOpen()
and
browseForSave()
methods,
upon selection the target File object points to the selected files.
The
browseForOpenMultiple
() method dispatches a
selectMultiple
event
when the user selects files. The
selectMultiple
event
is of type FileListEvent, which has a
files
property that
is an array of File objects (pointing to the selected files).
For example, the following code presents the user with an “Open”
dialog box in which the user can select a file:
var fileToOpen = air.File.documentsDirectory;
selectTextFile(fileToOpen);
function selectTextFile(root)
{
var txtFilter = new air.FileFilter("Text", "*.as;*.css;*.html;*.txt;*.xml");
root.browseForOpen("Open", new window.runtime.Array(txtFilter));
root.addEventListener(air.Event.SELECT, fileSelected);
}
function fileSelected(event)
{
trace(fileToOpen.nativePath);
}
If the application has another browser dialog box open when you
call a browse method, the runtime throws an Error exception.
Modifying File paths
You
can also modify the path of an existing File object by calling the
resolvePath()
method
or by modifying the
nativePath
or
url
property of
the object, as in the following examples (on Windows):
file1 = air.File.documentsDirectory;
file1 = file1.resolvePath("AIR Test");
alert(file1.nativePath); // C:\Documents and Settings\userName\My Documents\AIR Test
var file2 = air.File.documentsDirectory;
file2 = file2.resolvePath("..");
alert(file2.nativePath); // C:\Documents and Settings\userName
var file3 = air.File.documentsDirectory;
file3.nativePath += "/subdirectory";
alert(file3.nativePath); // C:\Documents and Settings\userName\My Documents\subdirectory
var file4 = new air.File();
file4.url = "file:///c:/AIR Test/test.txt";
alert(file4.nativePath); // C:\AIR Test\test.txt
When using the
nativePath
property, use the
forward slash (/) character as the directory separator character.
On Windows, you can use the backslash (\) character as well, but
you should not do so, as it leads to code that does not work cross-platform.
Supported AIR URL schemes
In
AIR, you can use any of the following URL schemes in defining the
url
property
of a File object:
URL scheme
|
Description
|
file
|
Use to specify a path relative to the root
of the file system. For example:
file:///c:/AIR Test/test.txt
The
URL standard specifies that a file URL takes the form
file://<host>/<path>
.
As a special case,
<host>
can be the empty
string, which is interpreted as "the machine from which the URL
is being interpreted." For this reason, file URLs often have three
slashes (///).
|
app
|
Use to specify a path relative to the root
directory of the installed application (the directory that contains the
application.xml file for the installed application). For example,
the following path points to an images subdirectory of the directory
of the installed application:
|
app-storage
|
Use to specify a path relative to the application
store directory. For each installed application, AIR defines a unique
application store directory, which is a useful place to store data
specific to that application. For example, the following path points
to a prefs.xml file in a settings subdirectory of the application
store directory:
app-storage:/settings/prefs.xml
|
Finding the relative path between two files
You can use the
getRelativePath()
method
to find the relative path between two files:
var file1 = air.File.documentsDirectory
file1 = file1.resolvePath("AIR Test");
var file2 = air.File.documentsDirectory
file2 = file2.resolvePath("AIR Test/bob/test.txt");
alert(file1.getRelativePath(file2)); // bob/test.txt
The second parameter of the
getRelativePath()
method,
the
useDotDot
parameter, allows for
..
syntax
to be returned in results, to indicate parent directories:
var file1 = air.File.documentsDirectory;
file1 = file1.resolvePath("AIR Test");
var file2 = air.File.documentsDirectory;
file2 = file2.resolvePath("AIR Test/bob/test.txt");
var file3 = air.File.documentsDirectory;
file3 = file3.resolvePath("AIR Test/susan/test.txt");
alert(file2.getRelativePath(file1, true)); // ../..
alert(file3.getRelativePath(file2, true)); // ../../bob/test.txt
Obtaining canonical versions of file names
File and path names are not case sensitive on Windows and Mac
OS. In the following, two File objects point to the same file:
File.documentsDirectory.resolvePath("test.txt");
File.documentsDirectory.resolvePath("TeSt.TxT");
However, documents and directory names do include capitalization.
For example, the following assumes that there is a folder named
AIR Test in the documents directory, as in the following examples:
var file = air.File.documentsDirectory;
file = file.resolvePath("AIR test");
trace(file.nativePath); // ... AIR test
file.canonicalize();
alert(file.nativePath); // ... AIR Test
The
canonicalize()
method converts the
nativePath
object
to use the correct capitalization for the file or directory name.
On case sensitive file systems (such as Linux), when multiple files
exists with names differing only in case, the
canonicalize()
method
adjusts the path to match the first file found (in an order determined
by the file system).
You can also use the
canonicalize()
method to
convert short file names ("8.3" names) to long file names on Windows,
as in the following examples:
var path = new air.File();
path.nativePath = "C:\\AIR~1";
path.canonicalize();
alert(path.nativePath); // C:\AIR Test
Working with packages and symbolic links
Various operating systems support package files and symbolic
link files:
Packages
—On Mac OS, directories can be designated
as packages and show up in the Mac OS Finder as a single file rather
than as a directory.
Symbolic links
—Mac OS, Linux, and Windows Vista
support symbolic links. Symbolic links allow a file to point to
another file or directory on disk. Although similar, symbolic links
are not the same as aliases. An alias is always reported as a file
(rather than a directory), and reading or writing to an alias or
shortcut never affects the original file or directory that it points
to. On the other hand, a symbolic link behaves exactly like the
file or directory it points to. It can be reported as a file or
a directory, and reading or writing to a symbolic link affects the
file or directory that it points to, not the symbolic link itself.
Additionally, on Windows the
isSymbolicLink
property
for a File object referencing a junction point (used in the NTFS
file system) is set to
true
.
The File class includes the
isPackage
and
isSymbolicLink
properties
for checking if a File object references a package or symbolic link.
The following code iterates through the user’s desktop directory,
listing subdirectories that are
not
packages:
var desktopNodes = air.File.desktopDirectory.getDirectoryListing();
for (i = 0; i < desktopNodes.length; i++)
{
if (desktopNodes[i].isDirectory && !!desktopNodes[i].isPackage)
{
air.trace(desktopNodes[i].name);
}
}
The following code iterates through the user’s desktop directory,
listing files and directories that are
not
symbolic links:
var desktopNodes = air.File.desktopDirectory.getDirectoryListing();
for (i = 0; i < desktopNodes.length; i++)
{
if (!desktopNodes[i].isSymbolicLink)
{
air.trace(desktopNodes[i].name);
}
}
The
canonicalize()
method changes the path of
a symbolic link to point to the file or directory to which the link
refers. The following code iterates through the user’s desktop directory,
and reports the paths referenced by files that are symbolic links:
var desktopNodes = air.File.desktopDirectory.getDirectoryListing();
for (i = 0; i < desktopNodes.length; i++)
{
if (desktopNodes[i].isSymbolicLink)
{
var linkNode = desktopNodes[i];
linkNode.canonicalize();
air.trace(desktopNodes[i].name);
}
}
Determining space available on a volume
The
spaceAvailable
property
of a File object is the space available for use at the File location,
in bytes. For example, the following code checks the space available
in the application storage directory:
air.trace(air.File.applicationStorageDirectory.spaceAvailable);
If the File object references a directory, the
spaceAvailable
property indicates
the space in the directory that files can use. If the File object
references a file, the
spaceAvailable
property
indicates the space into which the file could grow. If the file
location does not exist, the
spaceAvailable
property
is set to 0. If the File object references a symbolic link, the
spaceAvailable
property
is set to space available at the location the symbolic link points
to.
Typically the space available for a directory or file is the
same as the space available on the volume containing the directory
or file. However, space available can take into account quotas and
per-directory limits.
Adding a file or directory to a volume generally requires more
space than the actual size of the file or the size of the contents
of the directory. For example, the operating system may require
more space to store index information. Or the disk sectors required
may use additional space. Also, available space changes dynamically.
So, you cannot expect to allocate all of the reported space for
file storage. For information on writing to the file system, see
Reading and writing files
.
The
StorageVolumeInfo.getStorageVolumes()
method
provides more detailed information on mounted storage volumes (see
Working with storage volumes
).
Opening files with the default system application
In AIR 2, you can open a file using the application registered
by the operating system to open it. For example, an AIR application
can open a DOC file with the application registered to open it.
Use the
openWithDefaultApplication()
method of
a File object to open the file. For example, the following code
opens a file named test.doc on the user’s desktop and opens it with
the default application for DOC files:
var file = air.File.deskopDirectory;
file = file.resolvePath("test.doc");
file.openWithDefaultApplication();
Note:
On Linux, the file’s MIME type, not the filename extension,
determines the default application for a file.
The following code lets the user navigate to an mp3 file and
open it in the default application for playing mp3 files:
var file = air.File.documentsDirectory;
var mp3Filter = new air.FileFilter("MP3 Files", "*.mp3");
file.browseForOpen("Open", [mp3Filter]);
file.addEventListener(Event.SELECT, fileSelected);
function fileSelected(event)
{
file.openWithDefaultApplication();
}
You cannot use the
openWithDefaultApplication()
method
with files located in the application directory.
AIR prevents you from using the
openWithDefaultApplication()
method
to open certain files. On Windows, AIR prevents you from opening
files that have certain filetypes, such as EXE or BAT. On Mac OS
and Linux, AIR prevents you from opening files that will launch
in certain application. (These include Terminal and AppletLauncher
on Mac OS; and csh, bash, or ruby on Linux.) Attempting to open
one of these files using the
openWithDefaultApplication()
method
results in an exception. For a complete list of prevented filetypes,
see the language reference entry for the
File.openWithDefaultApplication()
method.
Note:
This limitation does not exist for an AIR application installed
using a native installer (an extended desktop application).
|
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