Adobe Air null object reference only on iOS - ios

Question

I am building a fairly large Adobe AIR application that targets iOS
The following exception is appearing in my file loading class, but only on iOS (PC works fine):
[Fault] exception, information=TypeError: Error #1009: Cannot access a property or method of a null object reference.
This occurs during the "onComplete" call in the following function. It happened suddenly and there were no recent code changes that would have affected that area of the application.
Files are loaded at the beginning of each "scene". Each scene uses the loader to load several files (asset lists, layouts, etc.). This exception only happens on the second file of the third scene to be loaded. The invocation of file loading is handled by a manager and is identical for all scenes. The data for the erroneous load is not corrupt and is successfully loaded before the exception on the onComplete call.
private function onFileLoaded( evt:Event ):void
{
trace( "onFileLoaded" );
var fs:FileStream = evt.currentTarget as FileStream;
var id:uint = m_fileStreamToId[ fs ];
var onComplete:Function = m_fileStreamToCallback[ fs ];
var retVal:Object = null;
var success:Boolean = false;
try
{
retVal = JSON.parse( fs.readUTFBytes( fs.bytesAvailable ) );
success = true;
}
catch ( error:Error )
{
trace( error );
retVal = null;
}
fs.close();
delete m_fileStreamToId[ fs ];
delete m_fileStreamToCallback[ fs ];
onComplete( id, retVal, success );
}
onFileLoaded is only called by:
private function internalAsyncLoadFileFromDisk( id:uint, filePath:File, onComplete:Function ):void
{
var fs:FileStream = new FileStream();
fs.addEventListener( Event.COMPLETE, onFileLoaded );
fs.addEventListener( IOErrorEvent.IO_ERROR, onIoError );
m_fileStreamToId[ fs ] = id;
m_fileStreamToCallback[ fs ] = onComplete;
fs.openAsync( filePath, FileMode.READ );
}
and the onComplete function argument is always a local private function.
When the debugger announces the null object reference and points to onComplete, it should be noted that onComplete is not null and the class encapsulating the functions has not been disposed of. Also, I do not see the "onFileLoaded" printed in the trace.
The m_fileStreamToCallback and m_fileStreamToId were created to remove the use of nested functions during file loading. I had experienced null object exceptions when attempting to access member variables as well as cross-scope local variables from within nested anonymous functions on iOS (even though it always works fine on PC).
Lastly, when I try to step into the file loading class with the debugger before the erroneous call, the debugger will always throw an internal exception and disconnect from the application. It only throws this exception before the erroneous call. The debugger is able to enter it successfully for all previous loads. It is also able to break inside the erroneous function when the null object error triggers. It simply cannot enter the class by stepping into it.
Environment details:
Adobe AIR: 14
Apache Flex SDK: 4.12.1
Editor: FlashDevelop
Build system: Ant
Build system OS: Windows 7 x64
Target Device: iPad 4
Target OS: iOS 7
Update 1
The following is the public interface and the onComplete function. So cleanupAndFinalCallback is the function that is supposedly null. I will also add that I am able to successfully enter this scene from another path through the application. If I enter via multiplayer, it crashes when loading the layout. When I enter from single player it does not. Both paths are loading the same file from the disk.
//! Async load the json file from the disk.
//! #param onComplete function( functorArgs:*, retVal:Object, success:Boolean )
public function asyncLoadFileFromDisk( filePath:File, onComplete:CallbackFunctor ):void
{
var newId:uint = m_idGenerator.obtainId();
m_idToCallback[ newId ] = onComplete;
internalAsyncLoadFileFromDisk( newId, filePath, cleanupAndFinalCallback );
}
private function cleanupAndFinalCallback( id:uint, retVal:Object, success:Boolean ):void
{
var onComplete:CallbackFunctor = m_idToCallback[ id ];
delete m_idToCallback[ id ];
m_idGenerator.releaseId( id );
onComplete.executeWithArgs( retVal, success );
}
Update 2
Stepping trough the app near the error causes debugger to crash. However, if I set breakpoints along the execution path I can jump (F5) through execution near the error. So, as I stated above, onComplete is not null as is reported by the error. I was able to execute it and pass further along in execution. At some point, the debugger throws the null reference error and snaps back to that point in the code. I feel there may be something funny going on with the stack.

Answer 1

I suspected that there may have been some issue with the stack. So, immediately after the file was loaded and the scene transition occurred, I used a delayed call of 1s to make sure that the load call was a real asynchronous call.
It turned out that the problem was with the debugger. I still received the "null object reference" error. However, this time, it reported it in a swc that was used in my app. It appears that this report is correct.
When I remove the delayed call, the program reverts to reporting the incorrect error.