ios - 尝试使用 swift 将 XML 从 URL 解析为 PickerView

Question

我正在尝试使用 XMLParser 解析 XML 并将其放在 PickerView 上。这是我的代码:

主要代码:

import UIKit

class ViewController: UIViewController, XMLParserDelegate {
    @IBOutlet weak var containerView: UIView!
    @IBOutlet weak var pickerView: UIPickerView!
    @IBOutlet weak var Image: UIImageView!
    @IBOutlet weak var Button: UIButton!

    var arrayCategorias = [Categories]()

    var parser = XMLParser()

    override func viewDidLoad() {
        super.viewDidLoad()

        let urlString = URL(string: "http://thecatapi.com/api/categories/list")
        self.parser = XMLParser(contentsOf: urlString!)!
        let success:Bool = self.parser.parse()
        parser.delegate = self
        if success {
            print("success")
        } else {
            print("parse failure!")
        }

        print(arrayCategorias.count)
    }

    @IBAction func botonPulsado(_ sender: Any) {
    }

    func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String]) {
        if(elementName=="category")
        {
            let categoria = Categories()
            for string in attributeDict {
                let strvalue = string.value as NSString
                switch string.key {
                case "id":
                    categoria.id = strvalue.integerValue
                    break
                case "name":
                    categoria.name = strvalue as String
                    break
                default:
                    break
                }
            }
            arrayCategorias.append(categoria)
        }

        func parser(_ parser: XMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) {
        }

        func parser(_ parser: XMLParser, foundCharacters string: String) {
        }

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

类类别代码:

import Foundation

class Categories{
     var id: Int = 0
     var name: String = ""
 }        

我不知道到底是什么问题，但是当我尝试读取 arrayCategorias() 只是为了查看是否有任何数据时，它只显示 0。我在哪里捕获了错误，它向我显示:“解析失败”。

如果有人能帮助我，我只是一个 android 程序员，我不知道为什么它不起作用。

我需要帮助将数据放在 PickerView 上。

Answer 1

有一大堆问题:

1. 您在解析后设置了您的委托(delegate)，而您必须在调用parse() 之前执行此操作。

2. 您在 didStartElement 中实现了一些委托(delegate)方法。这些需要是您的解析器委托(delegate)的顶级方法。

3. 不相关的小问题，但是您的类名 Categories 不太正确，因为它代表一个“类别”，而不是很多。所以我将其重命名为 Category。 (我个人也会将其设为 struct，但这取决于您。)

4. 您的 id 和 name 值不是 category 元素的属性。它们是它们自己的元素，因此您必须分别解析它们(使用 foundCharacters 并在 category< 的 didEndElement 上构建 Category 对象.

5. 类别的 id 似乎是一个整数，所以我将 Category 的 id 设为 整数。

6. 您正在调用 XMLParser 的 parse()，它使用来自主线程的 URL。这是不可取的，因为您在主线程执行请求时阻塞了主线程。就个人而言，我会使用 URLSession 异步请求数据，在后台队列中处理它，并且只将模型对象的最终更新和 UI 更新分派(dispatch)到主队列。

   就我个人而言，我自己会采用带有 @escaping 完成处理程序的异步模式，以帮助将我在解析后触发的 UI 更新与解析本身隔离开

7. 风格问题，但我不会将所有这些 XMLParserDelegate 代码都放在 View Controller 中。至少，把它放在一个扩展中，这样它就可以很好地组织起来。更好的是，本着 single responsibility principle 的精神定义一个独立的解析器委托(delegate)对象。并确保您不会在 UI 可能引用它时意外更新 View Controller 模型对象。它更安全地确保线程安全，并使您的代码封装得更好。

将所有这些放在一起，您可以执行以下操作:

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
    }
    
}