Titanium中的CommonJS模块不进行回调

Question

我在Titanium mobile中有一个QRcode扫描程序CommonJS模块，我想添加成功并取消回调。

但是我的函数在模块中总是未定义。

我的模块：

var scanner = null,
    successCallback = null,
    cancelHandler = null;

function AndroidScanner(allowRotation, displayedMessage, allowMenu, allowInstructions, useLED){
    this.scanner = require("ti.barcode");
    if(allowRotation)
        this.scanner.allowRotation = allowRotation;

    if(displayedMessage)
        this.scanner.displayedMessage = displayedMessage;

    if(allowMenu)
        this.scanner.allowMenu = allowMenu;

    if(allowInstructions)
        this.scanner.allowInstructions = allowInstructions;

    if(useLED)
        this.scanner.useLED = useLED;

};

//successListener changes the event to a common one for iOS and Android
AndroidScanner.prototype.successListener = function(event) {
    Ti.API.info("Successcallback get: "+JSON.stringify(this.successCallback));

    this.successCallback({barcode: event.result});
};

//Starts the scanner, pass the view to add the scanner to
AndroidScanner.prototype.startScanning = function(view) {
    this.scanner.addEventListener('success', this.successListener);
    this.scanner.addEventListener('cancel', this.cancelHandler);
    this.scanner.capture({
        animate : true,
        overlay : null,
        showCancel : true,
        showRectangle : true,
        keepOpen : false
    });
};

//Removes event listeners from the scanner
AndroidScanner.prototype.stopScanning = function() {
    this.scanner.removeEventListener('success', this.successHandler);
    this.scanner.removeEventListener('cancel', this.cancelHandler);
};

//Add a success handler
AndroidScanner.prototype.successHandler = function(handler) {
    Ti.API.info("Successhandler set: "+JSON.stringify(handler));
    this.successCallback = handler;
};

//Add a cancel handler
AndroidScanner.prototype.cancelHandler = function(handler) {
    Ti.API.info("Cancelhandler set: "+JSON.stringify(handler));
    this.cancelHandler = handler;
};

module.exports = AndroidScanner;

在alloy.js中：

if(OS_ANDROID) {
    var AndroidScanner = require("/ui/AndroidScanner");
    Alloy.Globals.scanner = new AndroidScanner(
        true,
        '',
        false,
        false,
        false
    );
}

Alloy.Globals.scanner.successHandler(function(e) {
    Alloy.Globals.barcodeScannerOn = false;
    //on successful scanning we know that windows is back
    Alloy.Globals.barcodeScanSuccesfull = true;
    Alloy.Globals.barcodeScanCanceled = false;
    Alloy.Globals.scanner.stopScanning();
    Alloy.Globals.barcodeScanResult = e.barcode;
    Ti.API.info('scan result' + JSON.stringify(Alloy.Globals.barcodeScanResult));
});

Alloy.Globals.scanner.cancelHandler(function(e) {
    Alloy.Globals.barcodeScannerOn = false;
    Alloy.Globals.barcodeScanCanceled = true;
    Alloy.Globals.barcodeScanSuccesfull = false;
    Alloy.Globals.scanner.stopScanning();
});

日志始终显示：

[INFO] :   Successhandler set: undefined
[INFO] :   Cancelhandler set: undefined

为什么会这样？