在iOS 14的WidgetView扩展中解析RSS XML

Question

我在应用程序的Swift中设置了一个XMLParser，希望能够在小部件扩展中解析RSS提要，并在小部件中返回数据。然而，我在让两个Swift文件相互交谈时遇到了一些问题。在Parser中，我有：

struct RSSItem {
var title: String
var description: String
var link: String
var pubDate: String
}
// download xml from the internet
class FeedParser: NSObject, XMLParserDelegate
{
private var rssItems: [RSSItem] = []
private var currentElement = ""
private var currentTitle: String = ""
private var currentDescription: String = ""
private var currentPubDate: String = ""
private var currentLink: String = ""

private var parserCompletionHandler: (([RSSItem]) -> Void)?

func parseFeed(url: String, completionHandler: (([RSSItem]) -> Void)?)
{
self.parserCompletionHandler = completionHandler

let request = URLRequest(url: URL(string: url)!)
let urlSession = URLSession.shared
let task = urlSession.dataTask(with: request) { (data, response, error) in
guard let data = data else {
if let error = error {
print(error.localizedDescription)
}

return
}

/// parse our xml data
let parser = XMLParser(data: data)
parser.delegate = self
parser.parse()
}

task.resume()
}
// MARK: - XML Parser Delegate
func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String] = [:]) {
if currentElement == "item" {
currentTitle = ""
currentDescription = ""
currentPubDate = ""
currentLink = ""
}
}
func parser(_ parser: XMLParser, foundCharacters string: String) {
switch currentElement {
case "title": currentTitle += string
case "description": currentDescription += string
case "pubDate" : currentPubDate += string
case "link" : currentLink += string
default: break
}
}
func parser(_ parser: XMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) {
if elementName == "item" {
let rssItem = RSSItem(title: currentTitle, description: currentDescription, link: currentLink, pubDate: currentPubDate)
self.rssItems.append(rssItem)
}
}
func parserDidEndDocument(_ parser: XMLParser) {
parserCompletionHandler?(rssItems)
}

func parser(_ parser: XMLParser, parseErrorOccurred parseError: Error) {
print(parseError.localizedDescription)
}
}

在小工具中，我有：

struct Provider: TimelineProvider {
@State private var rssItems:[RSSItem]?
let feedParser = FeedParser()
func placeholder(in context: Context) -> SimpleEntry {
SimpleEntry(date: Date(), title:"News", description: "Stuff happened", link: "Http://link", pubDate: "The day it posted")
}
func getSnapshot(in context: Context, completion: @escaping (SimpleEntry) -> ()) {
let entry = SimpleEntry(date: Date(), title:"News", description: "Stuff happened", link: "Http://link", pubDate: "The day it posted")
completion(entry)
}
func getTimeline(in context: Context, completion: @escaping (Timeline<Entry>) -> ()) {
var entries: [SimpleEntry] = []
feedParser.parseFeed(url: "") {(rssItems) in
self.rssItems = rssItems
let currentDate = Date()
for hourOffset in 0 ..< 5 {
let entryDate = Calendar.current.date(byAdding: .hour, value: hourOffset, to: currentDate)!
let entry = SimpleEntry(date: entryDate, title:rssItems.title, description: rssItems.description, link: rssItems.link, pubDate: rssItems.pubDate)
entries.append(entry)

}
// Generate a timeline consisting of five entries an hour apart, starting from the current date.

}
let timeline = Timeline(entries: entries, policy: .atEnd)
completion(timeline)
}
}
struct SimpleEntry: TimelineEntry {
let date: Date
let title: String
let description: String
let link: String
let pubDate: String
}

但是，在TimelineProvider部分，它告诉我rssItems没有名为title、description、pubDate或link的成员

Answer 1

您不能在SwiftUI视图之外使用@State变量，这意味着您不能在TimelineProvider中使用它们。

你可以用WidgetCenter.shared.reloadAllTimelines():

1. 更新FeedParser以存储解析的RSSItems，并在完成时通知WidgetCenter：

class FeedParser: NSObject, XMLParserDelegate {
var rssItems: [RSSItem] = [] // make public, here you will store parsed RSSItems
func parseFeed(url: String) { // remove `completionHandler` form the function signature
...
}
func parserDidEndDocument(_ parser: XMLParser) {
// instead of calling `completionHandler` force reload the timeline
WidgetCenter.shared.reloadAllTimelines()
}
}

2. 在创建时间线时从FeedParser获取第一个RSSItem，并从中创建一个条目：

struct Provider: TimelineProvider {
// no `@State` variables here
let feedParser = FeedParser()
...
func getTimeline(in context: Context, completion: @escaping (Timeline<Entry>) -> ()) {
guard !feedParser.rssItems.isEmpty else { return }
let entry = SimpleEntry(date: Date(), rssItem: feedParser.rssItems[0])

let timeline = Timeline(entries: [entry], policy: .never)
completion(timeline)
}
}

3. 要使所有这些工作正常，您需要知道何时必须再次调用parseFeed函数(以刷新项(

您可以尝试观察订阅源的通知，当收到通知时，请致电：

feedParser.parseFeed(url: "some_feed")

(为此，您需要使用相同的FeedParser实例，因此可能需要将FeedParser移出提供程序(