NSXMLParser Simple Example

Question

Most of the examples of how to invoke the NSXMLParser are contained within complex projects involving Apps. What does a simple example that demonstrates the callbacks look l

Answer 1

Swift 4 Example - Parsing Xib-file.

import Foundation

class XMLTransformer: NSObject {

   private let parser: XMLParser
   private var stack = [Node]()
   private var tree: Node?

   init(data: Data) {
      parser = XMLParser(data: data)
      super.init()
      parser.delegate = self
   }
}

extension XMLTransformer {

   func transform() throws -> Node? {
      parser.parse()
      if let e = parser.parserError {
         throw e
      }
      assert(stack.isEmpty)
      assert(tree != nil)
      return tree
   }

}

extension XMLTransformer: XMLParserDelegate {

   func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String] = [:]) {
      guard let tag = Tag(rawValue: elementName) else {
         return
      }
      let node = Node(tag: tag, attributes: attributeDict, nodes: [])
      stack.append(node)
   }

   func parser(_ parser: XMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) {
      guard let tag = Tag(rawValue: elementName) else {
         return
      }
      let lastElement = stack.removeLast()
      assert(lastElement.tag == tag)
      if let last = stack.last {
         last.nodes += [lastElement]
      } else {
         tree = lastElement
      }
   }
}

extension XMLTransformer {

   enum Tag: String {
      case document
      case objects
      case tableViewCell, tableViewCellContentView
      case subviews
      case mapView
      case constraints, constraint
      case connections, outlet
   }
}

extension XMLTransformer {

   class Node {

      let tag: Tag
      let attributes: [String : String]
      var nodes: [Node]

      init(tag: Tag, attributes: [String : String], nodes: [Node] = []) {
         self.tag = tag
         self.attributes = attributes
         self.nodes = nodes
      }
   }
}

Usage:

let data = try xib(named: "MapTableViewCell")
let c = XMLTransformer(data: data)
let tree = try c.transform() // Here you have parsed XML in a Tree representation.