XMLParser Delegate Methods not Called

Question

I'm trying to abstract an XML parser into a custom class to run it from a VC. It compiles perfectly and my error handler shows up success. However, the actual delegate methods are skipped over. No data is getting parsed.

It all ran fine when I had every running it the VC, but I am now try to get away from spaghetti code.

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        let parser = XMLParserHelper()
        //try create file for persistent data
        //CreatePlist.createPlist()
        parser.runParser()
    }
}

class XMLParserHelper:  NSObject, XMLParserDelegate {
    //list type variables to hold XML values (update list base on XML structure):
    static var station: String = ""
    static var latitude: String = ""
    static var longitude: String = ""
    private static var code: String = ""
    private static var id: String = ""

    //reusable method type veriales (do not touch)
    static var strXMLData:String = ""
    static var currentElement:String = ""
    static var passData:Bool=false
    static var passName:Bool=false
    static var xmlParser = XMLParser()

    //parser methods
    func runParser(){
        let xmlPath = Bundle.main.url(forResource: "station", withExtension: "xml")
        let xmlParser = XMLParser(contentsOf: (xmlPath)!)
        xmlParser?.delegate = self
        let success:Bool = xmlParser!.parse()
        xmlParser?.parse()
        if success {
            print("parse success!")
            print(XMLParserHelper.currentElement)
        } else {
            print("parse failure!")
        }
    }

    private static func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String]) {
        XMLParserHelper.currentElement=elementName;
        if (elementName=="StationDesc" || elementName=="StationLatitude" || elementName=="StationLongitude" || elementName=="StationCode" || elementName=="StationId" ) {
            if (elementName=="StationDesc") {
                XMLParserHelper.passName=true;
            }
            XMLParserHelper.passData=true;
        }
    }

    private static func parser(_ parser: XMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) {
        XMLParserHelper.currentElement="";
        if (elementName=="StationDesc" || elementName=="StationLatitude" || elementName=="StationLongitude" || elementName=="StationCode" || elementName=="StationId" ) {
            if(elementName=="StationDesc") {
                XMLParserHelper.passName=false;
            }
            XMLParserHelper.passData=false;
        }
    }

    private static func parser(_ parser: XMLParser, foundCharacters string: String) {
        if (XMLParserHelper.passName) {
            XMLParserHelper.strXMLData=XMLParserHelper.strXMLData+"\n\n"+string
        }

        if (XMLParserHelper.passData) {
            //ready content for codable struct
            switch XMLParserHelper.currentElement {
            case "StationDesc":
                XMLParserHelper.station = string
            case "StationLatitude":
                XMLParserHelper.latitude = string
            case "StationLongitude":
                XMLParserHelper.longitude = string
            case "StationCode":
                XMLParserHelper.code = string
            case "StationId":
                XMLParserHelper.id = string
                print(string)

            default:
                XMLParserHelper.id = string
            }
        }
    }

    func parser(_ parser: XMLParser, parseErrorOccurred parseError: Error) {
        print("failure error: ", parseError)
    }
}

Use a guard in runParser if xmlParser is nil do a fatalError — David Hoerl
– David Hoerl, Commented Nov 10, 2018 at 13:47
Unrelated to your issue but you don't need ; in Swift and you don't need ( ) in an if statement. — rmaddy
– rmaddy, Commented Nov 10, 2018 at 16:05

OOPer · Accepted Answer · 2018-11-10 16:24:07Z

3

To make XMLParserDelegate methods work, all the methods needs to be non-static, non-private methods.

So, all the properties should also be non-static.

class XMLParserHelper: NSObject, XMLParserDelegate {

    //list type variables to hold XML values (update list base on XML structure):
    var station: String = ""
    var latitude: String = ""
    var longitude: String = ""
    private var code: String = ""
    private var id: String = ""

    //reusable method type veriales (do not touch)
    var strXMLData: String = ""
    var currentElement: String = ""
    var passData: Bool = false
    var passName: Bool = false

    //parser methods
    func runParser() {
        let xmlURL = Bundle.main.url(forResource: "station", withExtension: "xml")!
        let xmlParser = XMLParser(contentsOf: xmlURL)!
        xmlParser.delegate = self
        let success = xmlParser.parse()
        if success {
            print("parse success!")
            print(currentElement)
        } else {
            print("parse failure!")
        }
    }

    //MARK: XMLParserDelegate methods

    func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String]) {
        currentElement = elementName
        if elementName == "StationDesc"
        || elementName == "StationLatitude"
        || elementName == "StationLongitude"
        || elementName == "StationCode"
        || elementName == "StationId"
        {
            if elementName == "StationDesc" {
                passName = true
            }
            passData = true
        }
    }

    func parser(_ parser: XMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) {
        currentElement = ""
        if elementName == "StationDesc"
        || elementName == "StationLatitude"
        || elementName == "StationLongitude"
        || elementName == "StationCode"
        || elementName == "StationId"
        {
            if elementName == "StationDesc" {
                passName = false
            }
            passData = false
        }
    }

    func parser(_ parser: XMLParser, foundCharacters string: String) {
        if passName {
            strXMLData = strXMLData+"\n\n"+string
        }

        if passData {
            //ready content for codable struct
            switch currentElement {
            case "StationDesc":
                station = string
            case "StationLatitude":
                latitude = string
            case "StationLongitude":
                longitude = string
            case "StationCode":
                code = string
            case "StationId":
                id = string
                print(string)

            default:
                id = string
            }
        }
    }

    func parser(_ parser: XMLParser, parseErrorOccurred parseError: Error) {
        print("failure error: ", parseError)
    }
}

The XMLParser just needs to be held while parse() is running, so you have no need to declare xmlParser as a property of XMLParserHelper.

answered Nov 10, 2018 at 16:24

OOPer

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3 Comments

Always In Over a year ago

OOPer, you Gem, that worked perfectly - been struggling with this for some time so it was quite a feeling to see those parser methods getting called! I think I see now where I went wrong now, as my custom class was calling these parse methods I assumed them to type methods rather than instance methods (hence I marked them static/private, but as they are infact delegate methods they are not private or type methods.

rmaddy Over a year ago

@FrankFerdinandMcGovern Please don't forget to indicate that your question has been solved by clicking the checkmark to the left of the most helpful answer.

Always In Over a year ago

@maddy, thanks for reminder and pointer, quite new to SO, so was wondering about that - have updated accordingly

Shehata Gamal · Accepted Answer · 2018-11-10 12:55:50Z

0

You need a strong reference

class ViewController: UIViewController{
   var parser:XMLParserHelper!
   override func viewDidLoad() {
     super.viewDidLoad()
     parser = XMLParserHelper()
     parser.runParser()
   }
}

answered Nov 10, 2018 at 12:55

Shehata Gamal

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2 Comments

anon Over a year ago

Good answer. With no strong reference, the parser will be dealloc'd before it can do its job.

rmaddy Over a year ago

This is not the issue since runParser is not asynchronous.

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