尝试使用swift将XML从URL解析到PickerView

有一大堆问题:

1. 您已设置 delegate 在解析之后,而您必须在调用之前执行此操作 parse() .

2. 您在内部实现了一些委托方法 didStartElement . 这些必须是解析器委托的顶级方法。

3. 次要无关问题,但您的班级名称 Categories 不太正确,因为它代表一个“类别”,而不是很多。所以我把这个重命名为 Category . (我个人也会做一个 struct ,但这取决于你。)

4. 你的 id 和 name 值不是 category 要素它们是自己的元素,因此您必须单独解析它们(使用 foundCharacters 并构建 类别 didEndElement 属于 类别 .

5. 这个 身份证件 其中的个类别似乎是一个整数,因此我将 身份证件 属于 类别 一 Int

6. 你在打电话 的 XMLParser 这是使用来自主线程的URL。这是不可取的,因为当主线程执行请求时,您正在阻塞主线程。就我个人而言,我会使用 URLSession 要异步请求数据,请在后台队列中处理它,并且只将模型对象的最终更新和UI更新发送到主队列。

   就我个人而言,我自己会采用异步模式 @escaping 完成处理程序,帮助将解析后触发的UI更新与解析本身隔离开来

7. 风格上的问题,但我不会把这一切 XMLParserDelegate 视图控制器中的代码。至少,把它放在一个扩展中,这样它组织得很好。更好的是,按照 single responsibility principle 并确保在UI可能引用视图控制器模型对象时不会意外更新视图控制器模型对象。它更安全地确保了线程安全,并使您的代码封装得更好。

综上所述,你可以做如下事情:

struct Category {
    let id: Int
    let name: String
}

class ViewController: UIViewController {
    @IBOutlet weak var pickerView: UIPickerView!
    
    var categories = [Category]()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        startRequestAndParse() { categories, error in
            guard let categories = categories, error == nil else {
                print(error?.localizedDescription ?? "Unknown error")
                return
            }
            
            // if you got here, everything is OK, so update model and UI on main thread
            
            DispatchQueue.main.async {
                self.categories = categories
                print(self.categories)
                
                // trigger whatever UI update you want here, too;
                
                self.pickerView.reloadAllComponents()
            }
        }
    }
    
    /// Initiate request from server and parse results
    ///
    /// - Parameters:
    ///     - completion: This is called when the request/parsing is done. This may be called
    ///                         on background thread. If parsing failed, the array of categories
    ///                         will be `nil` and we should have `error`.
    ///     - categories: First parameter of the `completion` closure is the array of `Category` objects, or `nil` on error.
    ///     - error:      Second parameter of the `completion` closure is the resulting `Error`, if any.

    private func startRequestAndParse(completion: @escaping (_ categories: [Category]?, _ error: Error?) -> Void) {
        let url = URL(string: "http://thecatapi.com/api/categories/list")!
        let task = URLSession.shared.dataTask(with: url) { data, _, error in
            guard let data = data, error == nil else {
                completion(nil, error)
                return
            }
            
            // ok, now parse
            
            let parser = XMLParser(data: data)
            let delegate = ParserDelegate()
            parser.delegate = delegate
            parser.parse()
            
            completion(delegate.categories, parser.parserError)
        }
        task.resume()
    }
}

// this assumes you set the picker's `delegate` to be the view controller (either in IB or programmatically in `viewDidLoad`

extension ViewController: UIPickerViewDelegate {
    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return categories[row].name
    }
}

// this assumes you set the picker's `dataSource` to be the view controller (either in IB or programmatically in `viewDidLoad`

extension ViewController: UIPickerViewDataSource {
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }
    
    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return categories.count
    }
}

/// Parser delegate for categories

class ParserDelegate: NSObject, XMLParserDelegate {
    private var id: Int?
    private var name: String?
    private var value: String?
    
    var categories: [Category]?
    
    // initialize `categories`
    
    func parserDidStartDocument(_ parser: XMLParser) {
        categories = []
    }
    
    // if `id` or `name`, initialize `value` so we'll capture the appropriate value
    
    func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String]) {
        if elementName == "id" || elementName == "name" {
            value = ""
        }
    }
    
    // if `value` is not `nil`, go ahead and concatenate the additional characters
    
    func parser(_ parser: XMLParser, foundCharacters string: String) {
        value? += string
    }
    
    // if `id` or `name`, update the appropriate property
    // if `category`, build a `Category` object and add it to our array
    // regardless, reset `value` to `nil`
    
    func parser(_ parser: XMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) {
        switch elementName {
        case "id":
            if let value = value {
                id = Int(value)
            }
        case "name":
            name = value
        case "category":
            if let id = self.id, let name = self.name {
                categories!.append(Category(id: id, name: name))
            }
            id = nil
            name = nil
        default:
            ()
        }
        value = nil
    }
    
    // if any error, reset `categories` so caller knows there was an issue
    
    func parser(_ parser: XMLParser, parseErrorOccurred parseError: Error) {
        categories = nil
    }
    
}