问题描述
因此,此代码对我在操场上有效,但由于某种原因URLSession.shared.dataTask(...
并未调用当前在本地运行的Flask API。有什么问题的主意吗?到目前为止,我只关心为什么它没有在我的项目中输入do{
,而是在操场上正常工作。
func getWords() -> [Word]{
var words = [Word]()
let url = URL(string: self.url)
let request = URLRequest(url: url!)
let group = dispatchGroup()
print("XD")
URLSession.shared.dataTask(with: request,completionHandler: { (data,response,error) in
do {
print("A")
if let data = data{
print("B")
if let decodedResponse = try? JSONDecoder().decode([Word].self,from: data){
group.enter()
dispatchQueue.main.async(){
words = decodedResponse
print("C")
print(words)
group.leave()
}
}
}
print("DD")
} catch {
print("Words.swift Error in try catch")
}
group.enter()
}).resume()
group.leave()
group.notify(queue: dispatchQueue.main,execute: {
print(words)
})
print("ASDASD WORDS: \(words)")
for _ in 1 ... 4 {
// - to make sure there aren't duplicates -
var wordId:Int = Int.random(in: 0..<words.count)
while randomIds.contains(wordId){
wordId = Int.random(in: 0..<words.count)
}
randomIds.append(wordId)
}
//returns 4 words
return words
}
解决方法
您没有正确使用DispatchGroup
;您应该在开始异步工作之前调用enter
,并在完成异步操作后调用leave
。然后,您可以使用notify
执行某些操作。
但是,在这种情况下,您实际上并不需要DispatchGroup
;之所以这样,是因为您试图将异步操作转变为同步操作;
正确的方法是接受操作是异步的,并且该功能不可能return
[Word]
。您将需要重构该函数以接受完成处理程序闭包,然后使用结果调用该闭包。
类似这样的东西:
func getWords(completionHandler:@escaping (Result<[Word],Error>) -> Void) -> Void{
var words = [Word]()
let url = URL(string: self.url)
let request = URLRequest(url: url!) // Note you should use a guard and call the completion handler with an error if url is `nil`
URLSession.shared.dataTask(with: request,completionHandler: { (data,response,error) in
if let error = error {
completionHandler(.failure(error))
} else {
do {
if let data = data {
let words = try JSONDecoder().decode([Word].self,from: data)
completionHandler(.success(words))
} else {
// TODO call completionHander with a .failure(SomeError)
}
} catch {
completionHandler(.failure(error))
}
}
}).resume()
}
然后您可以称之为:
getWords() { result in
switch result {
case .success(let words):
print(words)
case .failure(let error):
print(error.localizedDescription)
}
}