extjs4.1中出现Cannot read property 'fn' of undefined的错误

当给controller添加监听器（addListener）时，有时候会出现莫名其妙的错误：

比如 Cannot read property 'fn' of undefined，此时如果代码比较多的时候，不太好找错误，

此时可以用如下方法：

在 Ext.util.Observable中捕获错误的详细信息，添加红色代码即可，这样就可以找到错误原因了

addListener: function(ename, fn, scope, options) {

        var me = this,
            config, event, hasListeners,
            prevListenerCount = 0;


        if (typeof ename !== 'string') {
            options = ename;
            for (ename in options) {
                if (options.hasOwnProperty(ename)) {
                    config = options[ename];
                    if (!me.eventOptionsRe.test(ename)) {
                        if (typeof(config) == 'undefined') {
                            console.error('Cannot bind to event "' + ename + '" - method does not exist on object', options.scope);
                        } else {
                            me.addListener(ename, config.fn || config, config.scope || options.scope, config.fn ? config : options);
}
                    }
                }
            }
        } else {
            ename = ename.toLowerCase();
            event = me.events[ename];
            if (event && event.isEvent) {
                prevListenerCount = event.listeners.length;
            } else {
                me.events[ename] = event = new Ext.util.Event(me, ename);
            }


            // Allow listeners: { click: 'onClick', scope: myObject }
            if (typeof fn === 'string') {
                //<debug>
                if (!(scope[fn] || me[fn])) {
                    Ext.Error.raise('No method named "' + fn + '"');
                }
                //</debug>
                fn = scope[fn] || me[fn];
            }
            event.addListener(fn, scope, options);


            // If a new listener has been added (Event.addListener rejects duplicates of the same fn+scope)
            // then increment the hasListeners counter
            if (event.listeners.length !== prevListenerCount) {
                hasListeners = me.hasListeners;
                if (hasListeners.hasOwnProperty(ename)) {
                    // if we already have listeners at this level, just increment the count...
                    ++hasListeners[ename];
                } else {
                    // otherwise, start the count at 1 (which hides whatever is in our prototype
                    // chain)...
                    hasListeners[ename] = 1;
                }
            }

        }

比如：