ios - 为什么我的 XML 解析器不断迭代 Swift 中的标签？

Question

我正在尝试解析 XML 格式的天气数据，但我的解析器似乎在遍历所有标签，而不是我指定的标签。所以，我在我的 didStartElement 函数中有:

func parser(parser: NSXMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String])
{
    if(elementName == "cap:event") {
        capEventFound = true
    }
}

和我的 didEndElement 函数:

func parser(parser: NSXMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [NSObject : AnyObject])
{
    if(elementName == "cap:event") {
        capEventFound = false
    }
}

我的解析器函数:

func parser(parser: NSXMLParser, foundCharacters string: String)
{
    if(capEventFound)
    {
        newsStories.append(string)
        print(newsStories)
    }
    else
    {
        print("No cap:event found")
    }
}

解析的其他相关函数:

override func viewDidLoad() {
    super.viewDidLoad()
    self.pvState.delegate = self
    self.pvState.dataSource = self
    stateCode = ["AL", "AK", "AZ", "AR", "CA", "CO", "CT", "DE", "FL", "GA", "HI", "ID", "IL", "IN", "IA", "KS", "KY", "LA", "ME", "MD", "MA", "MI", "MN", "MS", "MO", "MT", "NE", "NV", "NH", "NJ", "NM", "NY", "NC", "ND", "OH", "OK", "OR", "PA", "RI", "SC", "SD", "TN", "TX", "UT", "VT", "VA", "WA", "WV", "WI", "WY"]
}

func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int
{
    return 1
}

func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int
{
    return stateCode.count
}

func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String?
{
    return stateCode[row]
}

func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int)
{
    selectedState = stateCode[pickerView.selectedRowInComponent(0)]
    url = "http://alerts.weather.gov/cap/\(selectedState).php?x=0"
    urlStr = url.stringByAddingPercentEncodingWithAllowedCharacters( NSCharacterSet.URLQueryAllowedCharacterSet())!
    searchURL = NSURL(string: urlStr as String)!
    xmlParser = NSXMLParser(contentsOfURL: searchURL)!
    xmlParser.delegate = self
    xmlParser.parse()
}

例如，当我选择科罗拉多时，我的输出是:http://pastebin.com/v3ULvQ0G

为什么要这样做，我怎样才能让它只发布相关的 cap:event？

Answer 1

它会继续遍历标签，因为它从不调用 didEndElement。这是因为您的 didEndElement 声明不正确，因此没有像您预期的那样被调用。本声明:

func parser(parser: NSXMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [NSObject : AnyObject]) { ... }

应该是:

func parser(parser: NSXMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) { ... }

---

不相关，但是您在 foundCharacters 中附加值的过程有点危险，因为理论上可能需要多次调用 foundCharacters 才能返回完整的事件名称。您通常应该只在 foundCharacters 中附加字符，并在 didEndElement 中更新您的模型结构。例如，我可能会建议:

var parsedString: String?

// element starts

func parser(parser: NSXMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String]) {
    if elementName == "cap:event" {
        parsedString = String()
    }
}

// characters found
//
// this may be called more than once

func parser(parser: NSXMLParser, foundCharacters string: String) {
    parsedString? += string
}

// element ended
//
// but, by the time we get here, we have the full parsed string 

func parser(parser: NSXMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) {
    if elementName == "cap:event" {
        newsStories.append(parsedString!)
        parsedString = nil
    }
}