在Swift Playground中使用以下代码

import UIKit

var str = "Hello,playground"

class Parse: NSObject,NSXMLParserDelegate{

func beginParse(){        
    let url = NSURL(string: "http://apps.wku.edu/iwku/maps/buildings/data/SouthCampus-Buildings.xml")
    var xml = NSXMLParser(contentsOfURL: url)

    xml?.delegate = self
    xml?.parse()
}

func parser(parser: NSXMLParser!,didStartElement elementName: String!,namespaceURI: String!,qualifiedName qName: String!,attributes attributeDict: NSDictionary!) {
    println("Element's name is \(elementName)")
    println("Element's attributes are \(attributeDict)")
    }
}

var instance = Parse()

instance.beginParse()

不幸的是我在控制台中的输出如下所示：

为什么我的attributeDict看起来是空的,如何访问与这些元素相关的值？