14. File Types

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Chapter 14. File Types

When a file type is associated with your AIR application, then every associated file of that type will open itself in your AIR application. This gives you great opportunities to work with external files in your AIR application. Registering Custom File Types discusses how to register a file type with your AIR application.

Before you begin, you should note that you make associations for an AIR application when installing the application, not at compile or debug time. This means you can’t test file associations until you package and install your application. When your application is packaged, the application descriptor XML file is read, and the file associations are set. This is not automatically done if another application on the system is already the default application; in other words, the AIR application install process does not override an existing file type association. If you want to take over the association from another application, take a look at Setting and Removing an Application as the Default Application for a File Type.

Registering Custom File Types

Problem

You want to register a custom file type so that the operating system will associate it with your AIR application.

Solution

Use the fileTypes element in the application descriptor file to declare the file types associated with your AIR application.

Discussion

Associations between your application and a file type must be declared in the application descriptor file. Depending on your environment and compiler settings, this descriptor file is typically the -app.xml file in your Adobe AIR project, characterized by the application root nodes. In that XML file, you can manipulate, for example, the initial, minimum, and maximum width and height; the initial position of your main AIR application window (see Chapter 2); and the file type associations.

An empty fileTypes node in the application descriptor file typically looks like this:

<fileTypes>
        <fileType>

            <name></name>
            <extension></extension>
            <description></description>
            <contentType></contentType>
            <icon>
                <image16x16></image16x16>
                <image32x32></image32x32>
                <image48x48></image48x48>
                <image128x128></image128x128>
            </icon>
        </fileType>
</fileTypes>

For each file type you want to register, you need to define a fileType node in the fileTypes element in your application descriptor XML file. The name and extension values are required, but the description and contentType values are optional. The name value is the name the system displays for the registered file. The extension is the extension for the file (not including the preceding period). You can use the same name for multiple extensions.

The description is shown to the user by the operating system user interface, such as when the user looks at the file properties.

The contentType property helps the operating system locate the best application to open a file in some special circumstances, such as when the extension is not recognized. The contentType property is required for any fileType property defined in the application descriptor file. The value of the contentType node is the name of the MIME type for the files.

Note

MIME stands for Multipurpose Internet Mail Extensions, and MIME types form standard ways of classifying file types. You can find an overview of common MIME types and their corresponding file extensions at http://www.webmaster-toolkit.com/mime-types.shtml.

Last but not least, you can also specify an icon for the file extension. The icon files must be included in the AIR installation file because they are not packaged automatically.

Setting an icon for the file extension is also optional. The path specified is relative to the installed AIR application root directory at runtime. Icon files must be in the PNG format, but you can specify different icon sizes. When all sizes are not provided, the closest size is scaled to fit for a given use of the icon by the operating system.

The following example shows a full fileTypes node from an application descriptor XML file:

    <fileTypes>
        <fileType>
            <name>Example.myOwnFileType</name>
            <extension>koen</extension>
            <description>This is a custom fileType that has my name
            </description>
            <contentType>text/plain</contentType>
            <icon>
                <image16x16>KOEN16.PNG</image16x16>
                <image32x32>KOEN32.PNG</image32x32>
                <image48x48>KOEN48.PNG</image48x48>
                <image128x128>KOEN128.PNG</image128x128>
            </icon>
        </fileType>
    </fileTypes>

According to the previous fileTypes node, if the user double-clicks a file called file.koen, then the associated AIR application will launch.

To retrieve the path to the specific file, you need to write a handler function for the InvokeEvent object dispatched by the NativeApplication object. The NativeApplication object represents the AIR application, and it can dispatch application-level events. If you want to open the file, you can use that specific path.

When the AIR application is invoked a second time, another instance of the application is not started. Instead, the first instance receives an additional invoke event.

If your AIR application is already running when the user double-clicks the associated file, AIR will immediately dispatch the InvokeEvent object to the running AIR application.

ActionScript

The following code illustrates how your AIR application can handle an invoke event dispatched by the runtime when an associated file is opened:

<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml"
    layout="absolute"
    applicationComplete="init()"
    >

    <mx:Script >
        <![CDATA[

            private function init():void{
                this.nativeApplication.addEventListener(InvokeEvent.INVOKE,invokeHandler);

            }
            private function invokeHandler(event:InvokeEvent):void{
                pathLabel.text = event.arguments[0];
            }

        ]]>
    </mx:Script>
    <mx:Label id="pathLabel" x="86" y="97" text="" fontSize="15"/>
</mx:WindowedApplication>

JavaScript

The following code shows how your AIR application can handle the invoke event that is dispatched by AIR when an associated file is opened:

<html >
<head>
<title>Recipe 14.1: File association</title>

<script src="AIRAliases.js" type="text/javascript"></script>

<script type="text/javascript">

function init(){
    air.NativeApplication.nativeApplication.addEventListener
(air.InvokeEvent.INVOKE,invokeHandler);

}

function invokeHandler(event){
    document.getElementById("textOutput1").innerHTML =  event.arguments[0];
}

</script>
</head>
<body onLoad="init()">

<div id="textOutput1">...</div>

</body>
</html>

Note

Keep in mind that you can test this file association functionality only by effectively making a release build of your AIR application and installing it on your system.

Determining Whether an Application Is the Default Application for a File Type

Problem

You want to check whether an AIR application is (still) the default application for a given file type on the user’s computer.

Solution

Use the isSetAsDefaultApplication method from the NativeApplication class.

Discussion

The AIR application installer does not override existing file associations, and file associations on a user’s system can change at any time (for example, when another program is installed). The best practice, therefore, is to verify that the expected file associations are in place when your application starts.

To determine whether an AIR application is the default application for a file type, you have to check the Boolean return value from the isSetAsDefaultApplication method. This method is part of the NativeApplication object that represents the AIR application.

ActionScript

The following code implements this little check mechanism. This code is placed into a function that is executed when the application is completely loaded:

private function init():void{

  if (NativeApplication.nativeApplication.isSetAsDefaultApplication("koen"){
    // *.koen files are already associated with this AIR app
  }else{
    //ask user to associate *.koen files  with this AIR app
  }

}

JavaScript

The following code implements this little check mechanism. This code is placed into a function that is executed when the application is completely loaded:

function init(){

  if (air.NativeApplication.nativeApplication.isSetAsDefaultApplication("koen"){
    // *.koen files are already associated with this AIR app
  }else{
    //ask user to associate *.koen files  with this AIR app
  }

}

Setting and Removing an Application as the Default Application for a File Type

Problem

You want to set or remove an AIR application as the default application for a file type.

Solution

Use the setAsDefaultApplication or removeAsDefaultApplication method from the NativeApplication class.

Discussion

AIR applications can manage associations for the file types that were originally declared in the application descriptor file (Registering Custom File Types). Even if a user has manually created an association between a file type and your AIR application, trying to set it as the default application will result in a runtime exception.

Suppose you declared a file type association in the descriptor file but the association is broken because another installed application took over the association. Because you originally defined the association, you can now set your AIR application as the default application.

To do this, you call the setAsDefaultApplication method and pass the file type extension as a parameter. This is a method of the nativeApplication object that represents the AIR application.

In the same way, you can remove an existing file type association by using the removeAsDefaultApplication method.

ActionScript

The following code shows how removeAsDefaultApplication and setAsDefaultApplication work. By using these two file type management methods, you can make sure your AIR application is always able to open the right files.

To set your AIR application to the default application for a file type, use the following code:

this.nativeApplication.setAsDefaultApplication("koen");

To remove your AIR application as the default application for a file type, use the following code:

this.nativeApplication.removeAsDefaultApplication("koen");

In Getting the Path of the Default Application for a File Type you can see a full ActionScript example that also shows these two file type management methods.

JavaScript

To set your AIR application as the default application for a file type, use the following code:

air.NativeApplication.nativeApplication.setAsDefaultApplication("koen");

To remove your AIR application as the default application for a file type, use the following code:

air.NativeApplication.nativeApplication.removeAsDefaultApplication("koen")

In Getting the Path of the Default Application for a File Type you can see a full JavaScript example that also shows these two file type management methods.

Getting the Path of the Default Application for a File Type

Problem

You want to know the path of the default application that is currently associated with a given file type.

Solution

Use the getDefaultApplication method from the NativeApplication class.

Discussion

If you want to know the path to the application that is associated with a given file type, you can pass the extension of that file type to the getDefaultApplication method from the nativeApplication object.

In ActionScript, to get the path of the default application, use the following code:

var path:String = this.nativeApplication.getDefaultApplication("koen");

In JavaScript, to get the path of the default application, use the following code:

var path = air.NativeApplication.nativeApplication.getDefaultApplication("koen");

Keep in mind, however, that this function works only on file types that are defined in the application descriptor file.

ActionScript

The following code combines all the recipes from this chapter in one example:

<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml"
 layout="vertical" applicationComplete="init()">
   <mx:Script>
      <![CDATA[


         private const FILE_EXTENSION:String = "acbtest";

         private function init():void
         {

            trace("[ch14] app init : start");

            this.nativeApplication.addEventListener(
               InvokeEvent.INVOKE,
               invokeHandler);

            textOutput1.text = "nativeApplication.isSetAsDefaultApplication : " +
               this.nativeApplication.isSetAsDefaultApplication(FILE_EXTENSION);

            textOutput2.text = "File.applicationDirectory.nativePath : " +
               File.applicationDirectory.nativePath;

            if (this.nativeApplication.isSetAsDefaultApplication(FILE_EXTENSION))
            {
               // remove the association
               this.nativeApplication.removeAsDefaultApplication(FILE_EXTENSION)
            }
            else
            {
              //set this app as default
               this.nativeApplication.setAsDefaultApplication(FILE_EXTENSION);
            }

            textOutput3.text = "nativeApplication.isSetAsDefaultApplication : " +
               this.nativeApplication.isSetAsDefaultApplication(FILE_EXTENSION);

            textOutput4.text = "nativeApplication.getDefaultApplication : " +
               this.nativeApplication.getDefaultApplication(FILE_EXTENSION);
         }

         private function invokeHandler(event:InvokeEvent):void
         {
            trace("[ch14] invokeHandler : " + event.arguments[0]); // trace the path
         }

      ]]>
   </mx:Script>


   <mx:Label id="textOutput1" />
   <mx:Label id="textOutput2" />
   <mx:Label id="textOutput3"/>
   <mx:Label id="textOutput4" />

</mx:WindowedApplication>

JavaScript

The following is the JavaScript:

<html>
<head>
<title>AIRCookbook CH14</title>

   <script src="AIRAliases.js" type="text/javascript"></script>
   <script type="text/javascript">

  var FILE_EXTENSION = "koen";

  function init()
  {
      air.trace("[ch14] app init : start");

      air.NativeApplication.nativeApplication.addEventListener(
         air.InvokeEvent.INVOKE,
         invokeHandler);

      document.getElementById("textOutput1").innerHTML = 
"nativeApplication.isSetAsDefaultApplication : " +
         air.NativeApplication.nativeApplication.isSetAsDefaultApplication(FILE_EXTENSION);

      document.getElementById("textOutput2").innerHTML = 
"air.File.applicationDirectory.nativePath : " +
         air.File.applicationDirectory.nativePath;

      if (air.NativeApplication.nativeApplication.isSetAsDefaultApplication(FILE_EXTENSION))
      {
         // remove the association
         air.NativeApplication.nativeApplication.removeAsDefaultApplication(FILE_EXTENSION)
      }
      else
      {
        //set this app as default
         air.NativeApplication.nativeApplication.setAsDefaultApplication(FILE_EXTENSION);
      }

      document.getElementById("textOutput3").innerHTML = 
"nativeApplication.isSetAsDefaultApplication : " +
         air.NativeApplication.nativeApplication.isSetAsDefaultApplication(FILE_EXTENSION);

      document.getElementById("textOutput4").innerHTML = 
"nativeApplication.getDefaultApplication : " +
         air.NativeApplication.nativeApplication.getDefaultApplication(FILE_EXTENSION);
   }

         function invokeHandler(event)
         {
            air.trace("[ch14] invokeHandler : " + event.arguments[0]); // trace the path
         }
</script>


</head>
<body onload="init();">
   <div id="textOutput1">...</div>
   <div id="textOutput2">...</div>
   <div id="textOutput3">...</div>
   <div id="textOutput4">...</div>
</body>
</html>

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Table of Contents for 14. File Types

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Chapter 14. File Types

Registering Custom File Types

Problem

Solution

Discussion

Note

ActionScript

JavaScript

Note

Determining Whether an Application Is the Default Application for a File Type

Problem

Solution

Discussion

ActionScript

JavaScript

Setting and Removing an Application as the Default Application for a File Type

Problem

Solution

Discussion

ActionScript

JavaScript

Getting the Path of the Default Application for a File Type

Problem

Solution

Discussion

ActionScript

JavaScript

Table of Contents for
14. File Types