Recipe for using the File promises API AIR 2.0

File promises is a new API (URLFilePromise) that allows you to access resources at a certain URL and drag them out of the AIR application as a file promise  into the local machine.  File promise, as the name suggests is a commitment that the file exists without actually checking. Once the files are dropped the request will be made to download the file to your local machine.

The URLFilePromise class implements the contract of IFilePromise using URLStream and URLRequest objects as the data source.

To create a URL file promise we create a URLFilePromise object, add the object to an array, and then start the drag passing the Clipboard object the array of file promises. See below.


var items:Array = fileData.selectedItems;
var promises:Array = new Array();
               
for each (var item:Object in items)
{
     var filePromise:URLFilePromise = new URLFilePromise();
     var request:URLRequest = new URLRequest(item.url);
                   
      filePromise.request = request;
      filePromise.relativePath = item.name;
      promises.push(filePromise);
 }

Take a look at the application below, which allows the dragging of items from a list into the user's local machine and then the copying of the files.

<?xml version="1.0" encoding="utf-8"?>
<s:WindowedApplication xmlns:fx="http://ns.adobe.com/mxml/2009"
                       xmlns:s="library://ns.adobe.com/flex/spark"
                      
xmlns:mx="library://ns.adobe.com/flex/mx">
    <fx:Script>
        <![CDATA[
            import air.desktop.URLFilePromise;
           
            import flash.desktop.Clipboard;
            import flash.desktop.ClipboardFormats;
            import flash.desktop.NativeDragManager;

            private var clipboard:Clipboard = new Clipboard();
           
            protected function onDragOut(event:MouseEvent):void
            {
                var items:Array = fileData.selectedItems;
                var promises:Array = new Array();
               
                for each (var item:Object in items)
                {
                    var filePromise:URLFilePromise = new
URLFilePromise();
                    var request:URLRequest = new
URLRequest(item.url);
                   
                    filePromise.request = request;
                    filePromise.relativePath = item.name;
                    promises.push(filePromise);
                }
               
               
clipboard.setData(ClipboardFormats.FILE_PROMISE_LIST_FORMAT,
promises);
                NativeDragManager.doDrag(fileData, clipboard);    
            }
           
            private function
onDragOutComplete(event:NativeDragEvent):void
            {
                trace( "onDragOutComplete" );
            }            

        ]]>
    </fx:Script>

    <fx:Declarations>
        <mx:ArrayCollection id="arrColl">
            <mx:source>
                <fx:Array>
                    <fx:Object name="rhall.jpg"
url="http://a1.twimg.com/profile_images/57117466/robert_m_hall_bio_photo_big_normal.jpg"
/>
                    <fx:Object name="bobjim.jpg"
url="http://a1.twimg.com/profile_images/51723308/ryancampbell3_normal.jpg"/>
                    <fx:Object name="jenschr.jpg"
url="http://a1.twimg.com/profile_images/43222252/jenschr_mugshot3_normal.jpg"/>
                    <fx:Object name="adamflater.jpg"
url="http://a1.twimg.com/profile_images/21503622/Photo_8_normal.jpg"/>
                    <fx:Object name="reboog711.jpg"
url="http://a1.twimg.com/profile_images/16984682/DSCF0044_normal.jpg"/>
                </fx:Array>
            </mx:source>
        </mx:ArrayCollection>
    </fx:Declarations>
    
    <mx:DataGrid id="fileData" dragEnabled="true"
                 dataProvider="{arrColl}"
                 mouseMove="onDragOut(event)"
                 nativeDragComplete="onDragOutComplete(event)">
        <mx:columns>
            <mx:DataGridColumn dataField="name" />
            <mx:DataGridColumn dataField="url"/>
        </mx:columns>
    </mx:DataGrid>
    
</s:WindowedApplication>

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