PhoneGap plugin: AudioEncode success callback never called - objective-c

Question

I'm using the AudioEncode plugin for PhoneGap (Cordova) on iOS. After updating a couple of lines for a newer version of Cordova, it appears to be correctly encoding wav files as m4a. In the Xcode console I see:
AVAssetExportSessionStatusCompleted
doing success callback
When I look at the file system on the phone, the wav file has indeed become a m4a. However, the success callback (where I upload the file to a server) is never run. This is the relevant code in the plugin:
-(void) doSuccessCallback:(NSString*)path {
NSLog(#"doing success callback");
NSString* jsCallback = [NSString stringWithFormat:#"%#(\"%#\");", self.successCallback, path];
[self writeJavascript: jsCallback];
[self.successCallback release];
}
My code in the app goes like this:
function encodeSuccess (path) {
console.log('Audio encoded to M4A! Preparing to upload...')
// file transfer code...
}
console.log('Preparing to encode audio file...')
window.plugins.AudioEncode.encodeAudio(entry.fullPath, encodeSuccess, fail)
I'm assuming the doSuccessCallback function in the plugin needs to be updated, but I don't have experience with Objective C or PhoneGap plugins, so I'm stuck at this point.
Any ideas?
UPDATE
In the Objective C function posted above, I tried logging self.successCallback, and it logged as <null>. Then I went up to the top of the main encodeAudio function, and the argument which is assigned to self.successCallback ([arguments objectAtIndex:1]) also logs as <null>. So, it seems to me that the callbacks are not being passed into the main function successfully.
This is the AudioEncode.h file, maybe someone can spot the problem here:
#interface AudioEncode : CDVPlugin {
NSString* successCallback;
NSString* failCallback;
}
#property (nonatomic, retain) NSString* successCallback;
#property (nonatomic, retain) NSString* failCallback;
- (void)encodeAudio:(NSArray*)arguments withDict:(NSDictionary*)options;

Answer 1

Ok, I figured this out by reading the basic examples in the Cordova Plugin Development Guide closely. The problem was with the ordering of parameters for cordova.exec(), which must have changed recently.
I plan to submit a pull request on GitHub with a working version of the plugin, but for now, here's the basic solution.
Before asking this question, I had updated the imports in AudioEncode.h from #import <PhoneGap/PGPlugin.h> to:
#import <Cordova/CDVPlugin.h>
#import <Cordova/CDVPluginResult.h>
Any reference to PGPlugin should also be updated to CDVPlugin, and PhoneGap should become cordova.
Here's the crux of the problem: in AudioEncode.js, cordova.exec() (where the original plugin calls PhoneGap.exec()) needs to be called like this:
AudioEncode.prototype.encodeAudio = function(audioPath, successCallback, failCallback) {
cordova.exec(successCallback, failCallback, "AudioEncode", "encodeAudio", [audioPath]);
};
If you don't order the parameters like this, the callbacks won't be passed in (although audioPath was...). Look at the docs for more details, but the parameters have to be the two callbacks first, the module name, the module action, and finally an array of extra parameters.
Then, you'll need to read in the parameters in the main encodeAudio function like this:
self.callback = [[arguments objectAtIndex:0] retain];
NSString* audioPath = [arguments objectAtIndex:1];
Note that there is only one callback object now, which contains references to the success and fail callbacks. This means that whenever the plugin sets up variables for successCallback and failCallback, you now only need callback (e.g. #synthesize callback). This is also declared in the AudioEncode.h file with #interface and #property.
Now, when actually firing the callbacks & returning data (in the doSuccessCallback and doFailCallback functions), you need to use CDVPluginResult, like this:
CDVPluginResult* pluginResult = nil;
NSString* javaScript = nil;
pluginResult = [CDVPluginResult resultWithStatus:CDVCommandStatus_OK messageAsString:path];
javaScript = [pluginResult toSuccessCallbackString:self.callback];
[self writeJavascript: javaScript];
[self.callback release];
Until I get the updated module up on GitHub, this should help anyone to get the plugin working.