A file promise is a drag-and-drop clipboard format that allows
a user to drag a file that does not yet exist out of an AIR application.
For example, using file promises, your application could allow a
user to drag a proxy icon to a desktop folder. The proxy icon represents
a file or some data known to be available at a URL. After the user
drops the icon, the runtime downloads the data and writes the file
to the drop location.
You can use the URLFilePromise class in an AIR application to
drag-and-drop files accessible at a URL. The URLFilePromise implementation
is provided in the aircore library as part of the AIR 2 SDK. Use
either the aircore.swc or aircore.swf file found in the SDK frameworks/libs/air
directory.
Alternately, you can implement your own file promise logic using
the IFilePromise interface (which is defined in the runtime flash.desktop
package).
File promises are similar in concept to deferred rendering using
a data handler function on the clipboard. Use file promises instead
of deferred rendering when dragging and dropping files. The deferred
rendering technique can lead to undesirable pauses in the drag gesture
as the data is generated or downloaded. Use deferred rendering for
copy and paste operations (for which file promises are not supported).
Limitations when using file promises
File
promises have the following limitations compared to other data formats
that you can put in a drag-and-drop clipboard:
-
File
promises can only be dragged out of an AIR application; they cannot
be dropped into an AIR application.
-
File promises are not supported on all operating systems.
Use the
Clipboard.supportsFilePromise
property
to test whether file promises are supported on the host system.
On systems that do not support file promises, you should provide
an alternative mechanism for downloading or generating the file
data.
-
File promises cannot be used with the copy-and-paste clipboard (
Clipboard.generalClipboard
).
