我正在构建一个函数,该函数接受CLLocation
参数,并返回我自己定义的DarkSkyResponse
类型的天气预报。
public func getForecast(at location: CLLocation) -> DarkSkyResponse {
let request = DarkSkyRequest(key: "KEYGOESHERE")
let point = DarkSkyRequest.Point(location.coordinate.latitude, location.coordinate.longitude)
guard let url = request.buildURL(point: point) else {
preconditionFailure("Failed to construct URL")
}
let task = URLSession.shared.dataTask(with: url) {
data, response, error in
DispatchQueue.main.async {
guard let data = data else {
fatalError("No Data Recieved")
}
guard let forecast = DarkSkyResponse(data: data) else {
fatalError("Decoding Failed")
}
return forecast
}
}
task.resume()
}
一切工作正常,我只想返回在DispatchQueue中找到的
forecast
变量。当我尝试执行此操作时,遇到以下错误:Unexpected non-void return value in void function
我相信这是因为我要返回DispatchQueue内部。为了解决这个问题,我将数据任务和解码过程移入了具有完成处理程序的函数中。当我调用该函数时,只需将闭包设置为按以下方式返回输出:
public func getForecast(at location: CLLocation) -> DarkSkyResponse {
let request = DarkSkyRequest(key: "KEYGOESHERE")
let point = DarkSkyRequest.Point(location.coordinate.latitude, location.coordinate.longitude)
guard let url = request.buildURL(point: point) else {
preconditionFailure("Failed to construct URL")
}
func getDataAndDecode(from url: URL, completionBlock: @escaping (DarkSkyResponse) -> Void) -> Void {
let task = URLSession.shared.dataTask(with: url) {
data, response, error in
DispatchQueue.main.async {
guard let data = data else {
fatalError("No Data Recieved")
}
guard let forecast = DarkSkyResponse(data: data) else {
fatalError("Decoding Failed")
}
completionBlock(forecast)
}
}
task.resume()
}
getDataAndDecode(from: url) { (output) in
return output
}
}
现在我得到一个警告:
Expression of type 'DarkSkyResponse' is unused
。我正在以正确的方式执行此操作,还是有一种更优雅的方式来返回我想要的值?
最佳答案
到目前为止,swift尚不支持异步等待样式(类似于javascript),这意味着您无法直接从异步操作中返回。
最好将callback(completionBlock)参数放在getForecast方法上。如果回调函数也处理错误的情况(例如onSuccess和onError),那就太好了。并且不要忘记将getForecast方法设置为void方法。
因此,就像这样:
func getForecast(at location: CLLocation, onSuccess: (DarkSkyResponse) -> (), onError: (Error) -> ()) {
...
}
关于ios - 从DispatchQueue Swift内部返回,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/60957291/