如何在Swift中使用OperationQueue下载和解析JSON
我陷入了一个概念上简单的问题。发生的情况是,解析操作在下载操作的完成处理程序完成之前执行。因此,没有需要解析的数据。您可以将以下代码直接放入文件并运行它 如何确保在运行解析操作之前完成下载如何在Swift中使用OperationQueue下载和解析JSON,json,swift,nsoperationqueue,Json,Swift,Nsoperationqueue,我陷入了一个概念上简单的问题。发生的情况是,解析操作在下载操作的完成处理程序完成之前执行。因此,没有需要解析的数据。您可以将以下代码直接放入文件并运行它 如何确保在运行解析操作之前完成下载 import UIKit let search = "https://api.nal.usda.gov/ndb/search/?format=json&q=butter&sort=n&max=25&offset=0&api_key=DEMO_KEY" class V
import UIKit
let search = "https://api.nal.usda.gov/ndb/search/?format=json&q=butter&sort=n&max=25&offset=0&api_key=DEMO_KEY"
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let fetch = FetchNBDNumbersOperation()
let parse = NDBParseOperation()
// 1
let adapter = BlockOperation() { [unowned parse, unowned fetch] in
parse.data = fetch.data
}
// 2
adapter.addDependency(fetch)
parse.addDependency(adapter)
// 3
let queue = OperationQueue()
queue.addOperations([fetch, parse, adapter], waitUntilFinished: true)
}
}
class FetchNBDNumbersOperation: Operation {
var data: Data?
override func main() {
let url = URL(string: search)!
let urlSession = URLSession.shared
let dataTask = urlSession.dataTask(with: url) { (jsonData, response, error) in
guard let jsonData = jsonData, let response = response else {
debugPrint(error!.localizedDescription)
return
}
self.data = jsonData
print("Response URL: \(String(describing: response.url?.absoluteString))")
}
dataTask.resume()
}
}
class NDBParseOperation: Operation {
var data: Data?
var nbdNumbers = [NBDNumber]()
override func main() {
let decoder = JSONDecoder()
do {
guard let jsonData = self.data else {
fatalError("No Data")
}
let dictionary = try decoder.decode( [String: USDAFoodSearch].self, from: jsonData )
for (_, foodlist) in dictionary {
for food in foodlist.item {
print("\(food.name) \(food.ndbno) \(food.group)")
let nbdNumber = NBDNumber(name: food.name, nbdNo: food.ndbno)
nbdNumbers.append(nbdNumber)
}
}
} catch {
print(error.localizedDescription)
}
}
}
struct NBDNumber {
var name: String
var nbdNo: String
}
struct USDAFoodSearch: Decodable {
let q: String
let sr: String
let ds: String
let start: Int
let end: Int
let total: Int
let group: String
let sort: String
let item: [USDAFood]
struct USDAFood: Decodable {
let offset: Int //Position in Array
let group: String
let name: String
let ndbno: String
let ds: String
}
}
您正在将其过度复杂化,甚至不需要使用OperationQueue,因为数据任务将异步完成 你可以这样做:
class FetchAndParse {
var data: Data?
var nbdNumbers = [NBDNumber]()
func fetch() {
let url = URL(string: search)!
let urlSession = URLSession.shared
let dataTask = urlSession.dataTask(with: url) { (jsonData, response, error) in
guard let jsonData = jsonData, let response = response else {
debugPrint(error!.localizedDescription)
return
}
self.data = jsonData
print("Response URL: \(String(describing: response.url?.absoluteString))")
self.parse()
}
dataTask.resume()
}
func parse() {
let decoder = JSONDecoder()
do {
guard let jsonData = self.data else {
fatalError("No Data")
}
let dictionary = try decoder.decode( [String: USDAFoodSearch].self, from: jsonData )
for (_, foodlist) in dictionary {
for food in foodlist.item {
print("\(food.name) \(food.ndbno) \(food.group)")
let nbdNumber = NBDNumber(name: food.name, nbdNo: food.ndbno)
nbdNumbers.append(nbdNumber)
}
}
print ("Finished With \(nbdNumbers.count) Items")
} catch {
print(error.localizedDescription)
}
}
}
let fp = FetchAndParse()
print ("Before Fetch")
fp.fetch()
print ("After Fetch")
然后您可以这样使用:
class FetchAndParse {
var data: Data?
var nbdNumbers = [NBDNumber]()
func fetch() {
let url = URL(string: search)!
let urlSession = URLSession.shared
let dataTask = urlSession.dataTask(with: url) { (jsonData, response, error) in
guard let jsonData = jsonData, let response = response else {
debugPrint(error!.localizedDescription)
return
}
self.data = jsonData
print("Response URL: \(String(describing: response.url?.absoluteString))")
self.parse()
}
dataTask.resume()
}
func parse() {
let decoder = JSONDecoder()
do {
guard let jsonData = self.data else {
fatalError("No Data")
}
let dictionary = try decoder.decode( [String: USDAFoodSearch].self, from: jsonData )
for (_, foodlist) in dictionary {
for food in foodlist.item {
print("\(food.name) \(food.ndbno) \(food.group)")
let nbdNumber = NBDNumber(name: food.name, nbdNo: food.ndbno)
nbdNumbers.append(nbdNumber)
}
}
print ("Finished With \(nbdNumbers.count) Items")
} catch {
print(error.localizedDescription)
}
}
}
let fp = FetchAndParse()
print ("Before Fetch")
fp.fetch()
print ("After Fetch")
如果运行该命令,您将看到“Before Fetch”和“After Fetch”消息都在下载和解析完成之前显示,并且解析在正确获取之后发生
当然,您可能需要对其进行更新,以便类通知某些内容所有内容都已完成,因此可能需要一个完成处理程序或委托,但这将由您决定。在获取操作中,您可以继续执行
URLSessionDataTask
。此时,操作认为它已经完成了,因为它不知道其他线程上发生了什么,也不关心并发操作,并且它依赖(adapter
)启动。同时,URLSessionDataTask
仍在另一个线程上执行
从苹果的文档中,在NSOperation
对于非并发操作,通常只重写一个方法:
main()
URLSessionDataTask
s同时运行,因此您需要做更多的工作来将它们包装到NSOperation
中。为了包装并发操作,您需要:
…至少重写以下方法和属性:
start()
isAsynchronous
i执行
isFinished
NSOperation
在这方面有很多细节,但总而言之:您需要重写start()
而不是main()
,并让您的实现保持操作状态最新。您只是在使用main
操作队列方法。并且您没有向操作队列通知操作状态 由于jjatie
操作队列
需要isExecuting和isFinishedKVC通知队列操作已完成或正在执行
我的建议是,在进行如此复杂的操作之前,请先阅读文档
下面是一个示例代码
class WSOperations: Operation {
private var _executing = false
private var _finished = false
private var showHUD:HUDFlag = .show
override var isExecuting: Bool {
get {
return _executing
} set {
willChangeValue(forKey: "isExecuting")
_executing = newValue
didChangeValue(forKey: "isExecuting")
}
}
override var isFinished: Bool {
get {
return _finished
} set {
willChangeValue(forKey: "isFinished")
_finished = newValue
didChangeValue(forKey: "isFinished")
}
}
override func start() {
if isCancelled {
isFinished = true
return
}
isExecuting = true
func completeOperation() {
isFinished = true
isExecuting = false
Logger.log(message: "Operation finished")
}
//Your request
request = DataManager.sharedManager.getRequest(showHUD: showHUD, success: { (success, response) in
if let t = self.finishedBLock {
t.success(success, response)
}
completeOperation()
}, failure: { (error) in
if let t = self.finishedBLock {
t.failure(error)
}
completeOperation()
})
}
override func cancel() {
super.cancel()
if isExecuting {
isFinished = true
isExecuting = false
}
request?.cancel()
}
}
希望对您有所帮助以下是答案。使用下面的类的子类获取操作。并在Fetch Op completion处理程序的末尾告诉它操作已完成
class FetchNBDNumbersOperation: AsynchronousOperation {
var data: Data?
override func main() {
super.main()
let url = URL(string: search)!
let urlSession = URLSession.shared
let dataTask = urlSession.dataTask(with: url) { (jsonData, response, error) in
guard let jsonData = jsonData, let response = response else {
debugPrint(error!.localizedDescription)
return
}
self.data = jsonData
print("Response URL: \(String(describing: response.url?.absoluteString))")
self.state = .finished
}
dataTask.resume()
}
}
在此处找到异步子类:
以我的拙见,我认为您应该重新设计它,以便只包含一个包含“获取”和“解析”的操作。因此,当您完成获取数据,然后解析数据时,不需要为两者都单独操作,因为它们无论如何都是相互关联的。感谢您的建议,但是操作是必需的,因为还有其他操作依赖于前两个,如果没有它们,它将变成无法维护的混乱。您应该提到,最初,否则我们正在解决一个问题将信息减半的问题。有用的线索。谢谢。这是一个很好的解决方案,但是永远不要调用super.start(),也不需要super.main()。实际上,您并没有在代码中这样做,而是在注释中这样做。