问题描述
我绝对是Swift和编程的初学者。
我不知道如何从调用POST请求的函数传递响应到第二个视图控制器上的文本标签。我认为主线程可能出了点问题,但我不知道如何解决。我确实尝试搜索解决方案,但对我没有任何帮助。
这是我的功能:
func getBookTitle() -> String {
var bookTitle = ""
if let bookNameURL = URL(string: urlString) {
do {
let htmlString = try String(contentsOf: bookNameURL,encoding: .utf8)
let htmlContent = htmlString
do {
let doc = try SwiftSoup.parse(htmlContent)
do {
let bookNumber = try doc.select("a.dlink").attr("onclick")
let bookNumberTrim = bookNumber.trimmingCharacters(in: CharacterSet.decimalDigits.inverted).components(separatedBy: ",")
do {
let bookid = bookNumberTrim[0]
let passageid = bookNumberTrim[1]
print(bookid)
print(passageid)
//Get Book Title
let url:URL = URL(string: "\(urlString)/getname")!
let session = URLSession.shared
let request = NSMutableURLRequest(url: url)
request.httpMethod = "POST"
request.cachePolicy = NSURLRequest.CachePolicy.reloadIgnoringCacheData
let paramString = "bookid=\(bookid)&passageid=\(passageid)"
request.httpBody = paramString.data(using: String.Encoding.utf8)
let task = session.dataTask(with: request as URLRequest) { (data,response,error) in
guard let data = data,let _:URLResponse = response,error == nil else {
print("error")
return
}
let dataString = String(data: data,encoding: String.Encoding(rawValue: String.Encoding.utf8.rawValue))
do {
let doc: Document = try SwiftSoup.parse(dataString ?? "")
do {
let bTitle = try doc.select("div").first()
bookTitle = try bTitle!.text()
print(bookTitle)
}
} catch {
print(error)
}
}
task.resume()
}
} catch {
print(error)
}
}
} catch let error {
print("Error \(error)")
}
} else {
print("Something wrong")
}
return bookTitle
}
这就是我试图将数据传递到另一个VC的方式:
@IBAction func infoButtonPressed(_ sender: UIButton) {
performSegue(withIdentifier: "goToInfo",sender: sender)
}
override func prepare(for segue: UIStoryboardSegue,sender: Any?) {
if segue.identifier == "goToInfo" {
let destinationVC = segue.destination as! BookInfoVC
destinationVC.bookName = networkService.getBookTitle()
}
}
第二个VC:
class BookInfoVC: UIViewController {
@IBOutlet weak var bookTitle: UILabel!
var bookName: String!
override func viewDidLoad() {
super.viewDidLoad()
bookTitle.text = bookName
}
}
该函数的响应是一个字符串行。
非常感谢!
UPD: 我尝试在函数中实现完成处理程序,现在看起来像这样:
func getBookTitle(completion: @escaping (String) -> ()) {
if let bookNameURL = URL(string: urlString) {
do {
let htmlString = try String(contentsOf: bookNameURL,encoding: .utf8)
let htmlContent = htmlString
do {
let doc = try SwiftSoup.parse(htmlContent)
do {
let bookNumber = try doc.select("a.dlink").attr("onclick")
let bookNumberTrim = bookNumber.trimmingCharacters(in: CharacterSet.decimalDigits.inverted).components(separatedBy: ",")
do {
let bookid = bookNumberTrim[0]
let passageid = bookNumberTrim[1]
//MARK: - Fetch book title
let params = BookTitle(bookid: bookid,passageid: passageid)
AF.request("\(self.urlString)/getname",method: .post,parameters: params).validate(contentType: ["application/x-www-form-urlencoded"]).response { (response) in
if let data = response.data,let utf8Text = String(data: data,encoding: .utf8) {
do {
let html: String = utf8Text
let doc: Document = try SwiftSoup.parse(html)
do {
let parseTitle = try doc.select("div").first()
let bookTitle = try parseTitle!.text()
completion(bookTitle)
} catch {
print(error)
}
} catch {
print(error)
}
}
}
}
} catch {
print(error)
}
}
} catch let error {
print("Error \(error)")
}
} else {
print("Something wrong")
}
}
我称之为:
@IBAction func infoButtonPressed(_ sender: UIButton) {
self.performSegue(withIdentifier: "goToInfo",sender: self)
}
override func prepare(for segue: UIStoryboardSegue,sender: Any?) {
if segue.identifier == "goToInfo" {
let destinationVC = segue.destination as! BookInfoVC
networkService.getBookTitle { bookTitle in
destinationVC.bookName = bookTitle
print(bookTitle)
}
}
我尝试将DispatchQueue.main.async粘贴到各处,但是它仍然没有更新第二个VC上的文本标签。但是在主视图控制器中,它工作正常。
解决方法
简短的回答:您不能。您正在发出异步请求。该函数将在结果可用之前返回。您需要重写函数以使用完成处理程序。然后,当结果可用时,您将调用完成处理程序。在此板上对此进行了广泛的讨论。
编辑:
您更新后的getBookTitle(completion:)
函数看起来不错,但是现在您遇到了排序问题。
您的第一个视图控制器中的prepare(for segue:)
方法使用您的networkService.getBookTitle(completion:)
函数,并在完成处理程序中设置destinationVC.bookName
。
但是,请记住networkService.getBookTitle(completion:)
是异步运行的。它立即返回,等待网络结果,然后然后调用完成处理程序。
您的目标视图控制器(类型为BookInfoVC
)尝试通过其bookName
方法将viewDidLoad
安装到其UI中。在第一个视图控制器的viewDidLoad()
触发之后,prepare(for segue:)
被立即调用。在调用viewDidLoad时,bookName
很可能仍然为零。
您需要在BookInfoVC
的{{1}}属性上添加didSet方法,以使其响应书名的更改。可能看起来像这样:
bookName
如果您这样做,则在getBookTitle()的完成处理程序触发时,它将更改var bookName: String! {
didSet: {
bookTitle.text = bookName
}
}
。这将触发destinationVC.bookName
的{{1}} BookInfoVC
代码,并将更新后的bookName
安装到UI中。