如何从Swift中的闭包接收方法的输出

Question

如何接收[TweetSntimentClassifierInput]对象数组的输出，并将其进一步发送到我的预测模型？

我有一个数组，但在一个闭包中，这使它无法作为方法输出返回。如果我在闭包外初始化一个空数组，那么输出总是一个空的数组，因为获取闭包需要时间才能完成。

代码

struct TweetFetcher {
let tweetCount = 100
let swifter = Swifter(consumerKey: key, consumerSecret: secret)
func fetchTweets(with searchText: String) -> [TweetSentimentClassifierInput] {

swifter.searchTweet(using: searchText, lang: "en", count: tweetCount, tweetMode: .extended) {(results, searchMetadata) in
var tweets = [TweetSentimentClassifierInput]()
let data = results.description.data(using: .utf8)
do {
let decodedData = try JSONDecoder().decode([TweetData].self, from: data!)
} catch {
print("Error with decoding, (error)")
}
for tweet in decodedData {
let tweetForClassification = TweetSentimentClassifierInput(text: tweet.full_text)
tweets.append(tweetForClassification)
}
} failure: { (error) in
print("Error with the Twitter API request, (error)")
}
}
}

如何从闭包返回一个非空数组作为方法输出？

Answer 1

您应该使用completionHandler概念来实现如下异步操作：

struct TweetFetcher {
let tweetCount = 100
let swifter = Swifter(consumerKey: key, consumerSecret: secret)

func fetchTweets(with searchText: String, completion: @escaping ([TweetSentimentClassifierInput]?, Error?) -> Void) {

swifter.searchTweet(using: searchText, lang: "en", count: tweetCount, tweetMode: .extended) {(results, searchMetadata) in
var tweets = [TweetSentimentClassifierInput]()
let data = results.description.data(using: .utf8)

do {
let decodedData = try JSONDecoder().decode([TweetData].self, from: data!)
} catch {
print("Error with decoding, (error)")
completion(nil, error)
}

for tweet in decodedData {
let tweetForClassification = TweetSentimentClassifierInput(text: tweet.full_text)
tweets.append(tweetForClassification)
}
completion(tweets, nil)
} failure: { (error) in
print("Error with the Twitter API request, (error)")
completion(nil, error)
}
}
}

使用

let fetcher = TweetFetcher()
fetcher.fetchTweets(with: "Keyword...") { tweets, error in
if let error = error {
print(error.localizedDescription)
} else {
// Use tweets array content here ...
}
}

Answer 2

以异步方式转换此方法，传递以[TweetSentimentClassifierInput]作为闭包参数的闭包，并将一个错误作为辅助闭包参数

func fetchTweets(with searchText: String, finished: ((_ sentiments: [TweetSentimentClassifierInput]?,_ error: Error?) -> Void)) {
swifter.searchTweet(using: searchText, lang: "en", count: tweetCount, tweetMode: .extended) {(results, searchMetadata) in
var tweets = [TweetSentimentClassifierInput]()
let data = results.description.data(using: .utf8)
do {
let decodedData = try JSONDecoder().decode([TweetData].self, from: data!)
} catch {
print("Error with decoding, (error)")
}
for tweet in decodedData {
let tweetForClassification = TweetSentimentClassifierInput(text: tweet.full_text)
tweets.append(tweetForClassification)
}
finished(tweets, nil)
} failure: { (error) in
print("Error with the Twitter API request, (error)")
finished(nil, error)
}
}