Solving the “missing AIR application XML file” error in Flash Builder

Published on: April 17, 2010
Comments: No Comments

When creating an AIR project, you automatically get an XML configuration file for your application, which contains the initial width and height, the available icons and the indication whether or not the application uses a custom chrome (amongst other settings). This XML file has the same name as the application itself, followed by “-app.xml”. OK, so now you know what exactly I’m talking about, let me explain the problem.

When creating AIR applications, you often create custom components, which you place in separate packages to help organize the structure of your project. And every once in a while you will also create a custom component that extends the WindowedApplication class, for example to create an application that automatically updates itself when a new version becomes available. such a component would look like this:

public class AutoUpdater extends WindowedApplication {
  private var appUpdater:ApplicationUpdaterUI;
  public function AutoUpdater() {
    appUpdater = new ApplicationUpdaterUI();
    addEventListener(FlexEvent.APPLICATION_COMPLETE, startAutoUpdate);
  private function startAutoUpdate(event:FlexEvent):void {
    appUpdater.configurationFile = new File("app:/updateConfig.xml");
    appUpdater.isCheckForUpdateVisible = false;
    appUpdater.isDownloadUpdateVisible = false;
    appUpdater.isDownloadProgressVisible = false;
    appUpdater.addEventListener(UpdateEvent.INITIALIZED, autoUpdateInitialised);
  private function autoUpdateInitialised(event:UpdateEvent):void {

Now, you can simply extend your new application from this AutoUpdater class by declaring it as the root tag of your main application file. However, in Flash Builder 4 this generates an error, as shown in the picture below.

Compilation issues in Flash Builder

In this screenshot you notice there are two errors, since for my project I also created another custom class which implements the URL monitoring system as well, on top of the automatic updates. Apparently the compiler expects each application to have its own XML configuration file, even though those components are not the actual starting point for your application.

To solve this problem you simply have to go to the project settings dialog. In that dialog you go to the “Flex Applications” part by selecting it on the left side. Within that section you can see each application within your project – yes, a single project can contain more than one applications.

Flash Builder Project Settings

You can notice that the AutoUpdater class (and in my case the MonitoredAutoUpdater class as well) is flagged as an application. Just select that application and click the “Remove” button. This will not remove the file from the project, but instead it just removes the application flag. And because the compiler will no longer recognize it as an actual appliaction, it will not search for that XML configuration file anymore, thus solving your problem.

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