我是 Swift 的新手，我有一个关于同步调用的问题。
我想对 dataTaskWithRequest 进行同步调用，以便在 dataTaskWithRequest 完成后调用返回方法。这是我的代码:
private func sendRequest (request: NSURLRequest) -> NSData{
let session = NSURLSession.sharedSession()
var dataReceived: NSData = NSData ()
let task = session.dataTaskWithRequest(request) { data, response, error in
if error != nil{
print("Error -> \(error)")
return
}
dataReceived = data!
}
task.resume()
return dataReceived
}
最好的方法是什么？我已尝试使用完成处理程序，但我做不到。
非常感谢您的帮助。
您可以像这样将异步调用与信号量同步:
private func sendRequest(request: NSURLRequest) -> NSData? {
let session = NSURLSession.sharedSession()
var dataReceived: NSData?
let sem = dispatch_semaphore_create(0)
let task = session.dataTaskWithRequest(request) { data, response, error in
defer { dispatch_semaphore_signal(sem) }
if let error = error {
print("Error -> \(error)")
return
}
dataReceived = data
}
task.resume()
// This line will wait until the semaphore has been signaled
// which will be once the data task has completed
dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER)
return dataReceived
}
然后你像这样使用函数:
let url = NSURL(string: "http://www.google.com")!
let req = NSURLRequest(URL: url)
let data = sendRequest(req)
print("This is data: \(data)")
对于 Swift 5
原理是一样的，只是有些项目改名了。请注意，这还会显示请求的更多设置。
static func sendRequest() -> Data? {
let session = URLSession.shared
var dataReceived: Data?
let sem = DispatchSemaphore.init(value: 0)
let params = ["key" : "value"] as Dictionary<String, String>
let token = ""
var body = try? JSONSerialization.data(withJSONObject: params, options: [])
var request = URLRequest(url: URL(string: "https://example.com")!)
request.httpMethod = "POST"
request.httpBody = body
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
let task = session.dataTask(with: request) { data, response, error in
defer { sem.signal() }
if let error = error {
print("Error -> \(error)")
return
}
dataReceived = data
}
task.resume()
// This line will wait until the semaphore has been signaled
// which will be once the data task has completed
sem.wait()
return dataReceived
}
使用它
let data = sendRequest()