在Swift中从URL解析XML

Question

我是解析新手，找不到任何过时且未提出更多问题的教程。我正在尝试解析一个简单的xml文件url。xml非常简单：

<xml>
    <record>
        <EmpName>A Employee</EmpName>
        <EmpPhone>111-222-3333</EmpPhone>
        <EmpEmail>[e-mail]</EmpEmail>
        <EmpAddress>12345 Fake Street</EmpAddress>
        <EmpAddress1>MyTown, Mystate ZIP</EmpAddress1>
    </record>
</xml>

并且只想将其保存为NSDictionary（标签作为键，数据作为值）。到目前为止，我所能成功完成的工作是在控制台中使用以下命令打印xml字符串：

let url = NSURL(string: "http://www.urlexample.com/file.xml")

let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
        println(NSString(data: data, encoding: NSUTF8StringEncoding))
}
print(task)
task.resume()

我浏览过所有发现的在线教程，这些教程要么过时，要么过于复杂。任何帮助表示赞赏。

Answer 1

过程很简单：

1. 创建XMLParser对象，并向其传递数据。
2. delegate为该解析器指定。
3. 启动解析。

因此，在Swift 3/4中，它看起来像：

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()

问题是如何实现这些XMLParserDelegate方法。三种关键方法是didStartElement（准备接收字符的位置），foundCharacters（处理解析的实际值的位置）和didEndElement（保存结果的位置）。

您问过如何解析单个记录（即单个字典），但是我将向您展示一种更通用的模式来解析一系列记录，这是XML更为常见的情况。如果您不需要值数组（或只需获取第一个值），显然可以看到如何简化此过程。

// 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<String>(["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

和

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
    }

}