Parsing XML from URL in Swift

Question

I am brand new to parsing and cannot find any tutorial that isn\'t outdated and doesn\'t raise more questions. I have a simple xml file url I am trying to parse. The xml is

Answer 1

The process is simple:

1. Create XMLParser object, passing it the data.
2. Specify the delegate for that parser.
3. Initiate the parsing.

So, in Swift 3/4, that looks like:

let task = URLSession.shared.dataTask(with: url) { data, response, error in
    guard let data = data, error == nil else {
        print(error ?? "Unknown error")
        return
    }

    let parser = XMLParser(data: data)
    parser.delegate = self
    if parser.parse() {
        print(self.results ?? "No results")
    }
}
task.resume()

The question is how do you implement the XMLParserDelegate methods. The three critical methods are didStartElement (where you prepare to receive characters), foundCharacters (where you handle the actual values parsed), and didEndElement (where you save you results).

You asked how to parse a single record (i.e. a single dictionary), but I'll show you a more general pattern for parsing a series of them, which is a far more common situation with XML. You can obviously see how to simplify this if you didn't need an array of values (or just grab the first one).

// a few constants that identify what element names we're looking for inside the XML

// a few constants that identify what element names we're looking for inside the XML

let recordKey = "record"
let dictionaryKeys = Set(["EmpName", "EmpPhone", "EmpEmail", "EmpAddress", "EmpAddress1"])

// a few variables to hold the results as we parse the XML

var results: [[String: String]]?         // the whole array of dictionaries
var currentDictionary: [String: String]? // the current dictionary
var currentValue: String?                // the current value for one of the keys in the dictionary

And

extension ViewController: XMLParserDelegate {

    // initialize results structure

    func parserDidStartDocument(_ parser: XMLParser) {
        results = []
    }

    // start element
    //
    // - If we're starting a "record" create the dictionary that will hold the results
    // - If we're starting one of our dictionary keys, initialize `currentValue` (otherwise leave `nil`)

    func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String]) {
        if elementName == recordKey {
            currentDictionary = [:]
        } else if dictionaryKeys.contains(elementName) {
            currentValue = ""
        }
    }

    // found characters
    //
    // - If this is an element we care about, append those characters.
    // - If `currentValue` still `nil`, then do nothing.

    func parser(_ parser: XMLParser, foundCharacters string: String) {
        currentValue? += string
    }

    // end element
    //
    // - If we're at the end of the whole dictionary, then save that dictionary in our array
    // - If we're at the end of an element that belongs in the dictionary, then save that value in the dictionary

    func parser(_ parser: XMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) {
        if elementName == recordKey {
            results!.append(currentDictionary!)
            currentDictionary = nil
        } else if dictionaryKeys.contains(elementName) {
            currentDictionary![elementName] = currentValue
            currentValue = nil
        }
    }

    // Just in case, if there's an error, report it. (We don't want to fly blind here.)

    func parser(_ parser: XMLParser, parseErrorOccurred parseError: Error) {
        print(parseError)

        currentValue = nil
        currentDictionary = nil
        results = nil
    }

}

For Swift 2 rendition, see previous revision of this answer.