作为我应用中身份验证过程的一部分，用户可以使用他们的 Facebook 帐户登录 - 我正在使用 Facebook iOS SDK 来处理这个过程。身份验证完成后，我向 Facebook graph api 发出请求以获取用户配置文件数据(这是第一个异步请求)。第二个异步请求也是向 Facebook graph api 请求安装了该应用程序的用户好友列表。
此函数中的最后一个也是第三个请求向我开发的 API 发出异步 POST 请求，以发布从 Facebook 收集的所有数据。最后，一旦完成，用户就可以进入该应用程序。然而事实并非如此，似乎 Facebook 请求在向 API 发出 POST 请求之前没有完成，因此它会推送空白数据。我不介意对 Facebook 的前 2 个请求按什么顺序完成，但是我需要在允许用户进入应用程序之前将数据成功发布到 API。我试过使用信号量和调度组，但是当查看控制台时，事情没有按正确的顺序运行，我可以从 API 数据库中看到正在插入空值。
认证 Controller
// Successful login, fetch faceook profile
let group = DispatchGroup()
group.enter()
// Redirect to tab bar controller should not happen until fetchProfile() has finished
// Redirect should not happen if fetchProfile() errors
self.fetchProfile()
group.leave()
// Redirect to tab bar controller
let storyboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
let tabBarController = storyboard.instantiateViewController(withIdentifier: "tabBarController") as! UITabBarController
self.present(tabBarController, animated: true, completion: nil)
更新的 Facebook Fetch 配置文件
// Facebook Profile Request
func fetchProfile() {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "User")
let user = appDelegate.user
var facebookFriends = [String?]()
do {
let results = try managedContext?.fetch(fetchRequest)
fetchedUser = results![0] as? NSManagedObject
}
catch {
print("Error fetching User entity")
return
}
let group = DispatchGroup()
print("Starting Step 1")
group.enter()
// Facebook Profile
let parameters = ["fields": "id, email, first_name, last_name, picture.width(500).height(500), birthday, gender"]
FBSDKGraphRequest(graphPath: "me", parameters: parameters).start { (connection, result, error) -> Void in
if error != nil {
print(error)
return
}
let result = result as? NSDictionary
if let providerID = result?["id"] as? String {
user.provider_id = providerID
self.fetchedUser!.setValue(providerID, forKey: "provider_id")
}
if let firstName = result?["first_name"] as? String {
user.first_name = firstName
self.fetchedUser!.setValue(firstName, forKey: "first_name")
}
if let lastName = result?["last_name"] as? String {
user.last_name = lastName
self.fetchedUser!.setValue(lastName, forKey: "last_name")
}
if let email = result?["email"] as? String {
user.email = email
self.fetchedUser!.setValue(email, forKey: "email")
}
if let picture = result?["picture"] as? NSDictionary, let data = picture["data"] as? NSDictionary, let url = data["url"] as? String {
user.avatar = url
self.fetchedUser!.setValue(url, forKey: "avatar")
}
if let birthday = result?["birthday"] as? String {
user.birthday = birthday
self.fetchedUser!.setValue(sqlDate, forKey: "birthday")
}
if var gender = result?["gender"] as? String {
user.gender = gender
self.fetchedUser!.setValue(gender, forKey: "gender")
}
group.leave()
print("Step 1 Done")
group.enter()
print("Starting Step 2")
// Facebook Friends Request
FBSDKGraphRequest(graphPath: "me/friends", parameters: ["fields": "id, first_name, last_name, picture"]).start { (connection, result, error) -> Void in
if error != nil {
print(error)
return
}
let result = result as! [String:AnyObject]
for friend in result["data"] as! [[String:AnyObject]] {
let id = friend["id"] as! String
facebookFriends.append(id)
}
group.leave()
print("Step 2 Done")
// User POST Request
var dictionary = self.fetchedUser?.dictionaryWithValues(forKeys: ["provider", "provider_id", "first_name", "last_name", "email", "avatar", "birthday", "gender"])
if facebookFriends.count > 0 {
dictionary?["friends"] = facebookFriends
}
let data = NSMutableDictionary()
data.setValuesForKeys(dictionary!)
//let semaphore = DispatchSemaphore(value: 2)
group.enter()
print("Starting Step 3")
do {
// Here "jsonData" is the dictionary encoded in JSON data
let jsonData = try JSONSerialization.data(withJSONObject: data, options: .prettyPrinted)
// Here "decoded" is of type `Any`, decoded from JSON data
let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
// Final dict
if let dictFromJSON = decoded as? [String:String] {
let endpoint = "http://endpoint.com/user"
let url = URL(string: endpoint)
let session = URLSession.shared
var request = URLRequest(url: url!)
request.httpMethod = "POST"
request.httpBody = try JSONSerialization.data(withJSONObject: dictFromJSON, options: [])
request.addValue("application/json", forHTTPHeaderField: "Accept")
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
session.dataTask(with: request, completionHandler: { (data, response, error) -> Void in
if error != nil {
//semaphore.signal()
group.leave()
print(error)
return
}
do {
// Save response
let json = try(JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? [String: AnyObject])
if let userID = json?["user_id"] {
user.user_id = userID as? Int
self.fetchedUser!.setValue(userID, forKey: "user_id")
}
if let friends = json?["friends"] , !(friends is NSNull){
user.friends = friends as? [String]
self.fetchedUser!.setValue(friends, forKey: "friends")
}
group.leave()
//semaphore.signal()
} catch let jsonError {
print(jsonError)
return
}
}).resume()
}
} catch {
print(error.localizedDescription)
}
// Wait to async task to finish before moving on
//_ = semaphore.wait(timeout: DispatchTime.distantFuture)
print("Step 3 Done")
}
}
}
最佳答案
将每个闭包之后的代码移动到闭包本身内部，以便它在运行之前等到它之前的代码:
// Facebook Profile Request
func fetchProfile() {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "User")
let user = appDelegate.user
var facebookFriends = [String?]()
do {
let results = try managedContext?.fetch(fetchRequest)
fetchedUser = results![0] as? NSManagedObject
}
catch {
print("Error fetching User entity")
return
}
let group = DispatchGroup()
print("Starting Step 1")
group.enter()
// Facebook Profile
let parameters = ["fields": "id, email, first_name, last_name, picture.width(500).height(500), birthday, gender"]
FBSDKGraphRequest(graphPath: "me", parameters: parameters).start { (connection, result, error) -> Void in
if error != nil {
print(error)
return
}
let result = result as? NSDictionary
if let providerID = result?["id"] as? String {
user.provider_id = providerID
self.fetchedUser!.setValue(providerID, forKey: "provider_id")
}
if let firstName = result?["first_name"] as? String {
user.first_name = firstName
self.fetchedUser!.setValue(firstName, forKey: "first_name")
}
if let lastName = result?["last_name"] as? String {
user.last_name = lastName
self.fetchedUser!.setValue(lastName, forKey: "last_name")
}
if let email = result?["email"] as? String {
user.email = email
self.fetchedUser!.setValue(email, forKey: "email")
}
if let picture = result?["picture"] as? NSDictionary, let data = picture["data"] as? NSDictionary, let url = data["url"] as? String {
user.avatar = url
self.fetchedUser!.setValue(url, forKey: "avatar")
}
if let birthday = result?["birthday"] as? String {
user.birthday = birthday
self.fetchedUser!.setValue(sqlDate, forKey: "birthday")
}
if var gender = result?["gender"] as? String {
user.gender = gender
self.fetchedUser!.setValue(gender, forKey: "gender")
}
group.leave()
print("Step 1 Done")
group.enter()
print("Starting Step 2")
// Facebook Friends Request
FBSDKGraphRequest(graphPath: "me/friends", parameters: ["fields": "id, first_name, last_name, picture"]).start { (connection, result, error) -> Void in
if error != nil {
print(error)
return
}
let result = result as! [String:AnyObject]
for friend in result["data"] as! [[String:AnyObject]] {
let id = friend["id"] as! String
facebookFriends.append(id)
}
group.leave()
print("Step 2 Done")
// User POST Request
var dictionary = self.fetchedUser?.dictionaryWithValues(forKeys: ["provider", "provider_id", "first_name", "last_name", "email", "avatar", "birthday", "gender"])
if facebookFriends.count > 0 {
dictionary?["friends"] = facebookFriends
}
let data = NSMutableDictionary()
data.setValuesForKeys(dictionary!)
//let semaphore = DispatchSemaphore(value: 2)
group.enter()
print("Starting Step 3")
do {
// Here "jsonData" is the dictionary encoded in JSON data
let jsonData = try JSONSerialization.data(withJSONObject: data, options: .prettyPrinted)
// Here "decoded" is of type `Any`, decoded from JSON data
let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
// Final dict
if let dictFromJSON = decoded as? [String:String] {
let endpoint = "http://endpoint.com/user"
let url = URL(string: endpoint)
let session = URLSession.shared
var request = URLRequest(url: url!)
request.httpMethod = "POST"
request.httpBody = try JSONSerialization.data(withJSONObject: dictFromJSON, options: [])
request.addValue("application/json", forHTTPHeaderField: "Accept")
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
session.dataTask(with: request, completionHandler: { (data, response, error) -> Void in
if error != nil {
//semaphore.signal()
group.leave()
print(error)
return
}
do {
// Save response
let json = try(JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? [String: AnyObject])
if let userID = json?["user_id"] {
user.user_id = userID as? Int
self.fetchedUser!.setValue(userID, forKey: "user_id")
}
if let friends = json?["friends"] , !(friends is NSNull){
user.friends = friends as? [String]
self.fetchedUser!.setValue(friends, forKey: "friends")
}
group.leave()
//semaphore.signal()
} catch let jsonError {
print(jsonError)
return
}
}).resume()
}
} catch {
print(error.localizedDescription)
}
// Wait to async task to finish before moving on
//_ = semaphore.wait(timeout: DispatchTime.distantFuture)
print("Step 3 Done")
}
}
}
解释:当你做异步网络请求时，闭包就是所谓的转义，这意味着它们在函数返回后运行。例如，FBSDKGraphRequest.start 采用转义闭包，保存它，返回，在它返回后，在请求完成后运行闭包。这是故意的。否则，它将是同步的并阻塞您的代码，这将导致您的应用程序卡住(除非您使用 GCD 自己异步运行代码)。
TL;DR 在诸如 FBSDKGraphRequest.start 之类的函数返回后调用闭包，导致下一组在其完成之前开始。这可以通过放置它们使它们一个接一个地运行来解决。
关于Swift:按顺序执行多个异步请求。如何等待上一个请求完成？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/41428648/