Parse XML data in swift

Question

It's my first iOS application, and I kinda have some trouble with getting data from a XML. I need to get the song name and the artist from a XML file that looks like this:

<?xml version="1.0" encoding="utf-8"?>
<Schedule System="Jazler">
  <Event status="happening" startTime="19:14:30" eventType="song">
    <Announcement Display="Now On Air:"/>
    <Song title="E timpul">
      <Artist name="Revers">
      </Artist>
      <Jazler ID="16490"/>
      <PlayLister ID=""/>
      <Media runTime="03:03"/>
      <Expire Time="19:17:33"/>
    </Song>
  </Event>
</Schedule>

Until now I think I created the parser, but I have no idea how to get the data from it, and the online tutorials are confusing me a bit...

self.parser = XMLParser(contentsOf: URL(string:"http://localhost/jazler/NowOnAir.xml")!)!
self.parser.delegate = self as? XMLParserDelegate

let success:Bool = self.parser.parse()
if success {
    print("success")

} else {
    print("parse failure!")
}

Your help is much appreciated & thanks in advance.

Answer 1

Because your XML contains all of the values with attributes of the element, you don't need to implement foundCharacters. Just didStartElement, e.g., your parser delegate might look as simple as:

var song: String?
var artist: String?

func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String] = [:]) {
    switch elementName {
    case "Song":   song   = attributeDict["title"]
    case "Artist": artist = attributeDict["name"]
    default:       break
    }
}

Two observations:

1. I'd be inclined to pull this parsing code out of the view controller, though, and put it in a dedicated object, to help prevent "view controller bloat".

2. I'd also use URLSession in case the response to request happens to be a little slow. Generally, one should avoid using XMLParser(contentsOf:), because that performs the request synchronously.

   In your case, since you’re requesting the data from localhost, perhaps that’s less of a concern. But, still, it’s prudent to always perform HTTP requests asynchronously.

Anyway, that might yield something like:

class SongParser: NSObject {
    var song: String?
    var artist: String?
    
    class func requestSong(completionHandler: @escaping (String?, String?, Error?) -> Void) {
        let url = URL(string: "http://localhost/jazler/NowOnAir.xml")!
        let task = URLSession.shared.dataTask(with: url) { data, _, error in
            guard let data = data, error == nil else {
                DispatchQueue.main.async {
                    completionHandler(nil, nil, error)
                }
                return
            }
            
            let delegate = SongParser()
            let parser = XMLParser(data: data)
            parser.delegate = delegate
            parser.parse()
            DispatchQueue.main.async {
                completionHandler(delegate.song, delegate.artist, parser.parserError)
            }
        }
        task.resume()
    }
}

extension SongParser: XMLParserDelegate {
    func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String] = [:]) {
        switch elementName {
        case "Song":   song   = attributeDict["title"]
        case "Artist": artist = attributeDict["name"]
        default:       break
        }
    }
    
}

And you'd use it like so:

SongParser.requestSong { song, artist, error in
    guard let song = song, let artist = artist, error == nil else {
        print(error ?? "Unknown error")
        return
    }
    
    print("Song:", song)
    print("Artist:", artist)
}

Answer 2

First convert your xml into NSData and call the parser to parse it.

//converting into NSData
var data: Data? = theXML.data(using: .utf8)

//initiate  NSXMLParser with this data
var parser: XMLParser? = XMLParser(data: data ?? Data())

//setting delegate
parser?.delegate = self

//call the method to parse
var result: Bool? = parser?.parse()

parser?.shouldResolveExternalEntities = true

Now, you need to implement the NSXMLParser delegate into your class.

func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String] = [:]) {
currentElement = elementName
print("CurrentElementl: [\(elementName)]")
}

func parser(_ parser: XMLParser, foundCharacters string: String) {
print("foundCharacters: [\(string)]")
}

You will find the value under key of your xml.