Swift 控制流程：

Question

在我的代码下方，我尝试使用 Facebook SDK 获取我的好友列表并在另一个视图控制器上显示他们。我在函数loginViewShowingLoggedInUser中调用函数createFriendsInfo(data : NSArray)。正在调用该函数并将数据填充到数组中。

问题是在createFriendsInfo中的循环完成填充数组中的数据后，控件直接转到视图控制器。相反，它应该首先执行完函数中循环之后的语句，然后控制应该返回到 loginViewShowingLoggedInUser 应该执行 performSegueWithIdentifier: 的地方。

我是 Swift 的新手，我需要一些帮助来理解我的代码中的控制流。

import Foundation
import UIKit

class FBViewController : UIViewController, FBLoginViewDelegate {


    @IBOutlet var fbLogin: FBLoginView!
    var friendNames : [String] = []
    var friendPics : [UIImage] = []

    override func viewDidLoad() {
        super.viewDidLoad()
        //var fbl: FBLoginView = FBLoginView() //create login button on UIController
        //self.view.addSubview(fbl)
        // Do any additional setup after loading the view, typically from a nib.
        self.fbLogin.delegate = self
        self.fbLogin.readPermissions = ["public_profile", "email", "user_friends"]


    }

    func createFriendsInfo(data : NSArray)
    {
        println("Start Create")
        for i in 0...data.count {
            let valueDict : NSDictionary = data[i] as NSDictionary
            let userID = valueDict.objectForKey("id") as String
            self.friendNames.append(valueDict.objectForKey("name") as String)
            let id = valueDict.objectForKey("name") as String
            var url = NSURL (string : "http://graph.facebook.com/\(userID)/picture?type=large")
            let urlRequest = NSURLRequest(URL: url!)
            let session = NSURLSession.sharedSession()

            var response: AutoreleasingUnsafeMutablePointer<NSURLResponse?>=nil
            var error: NSErrorPointer = nil
            if let ImageData : NSData = NSURLConnection.sendSynchronousRequest(urlRequest, returningResponse: response, error:nil)?
            {
                var image = UIImage( data : ImageData)
                self.friendPics.append(image!)
                println("Image Appended")
            }
        }

        println("Create Friends Info \(self.friendNames.count) \(self.friendPics.count) ")
    }


    // Facebook Delegate Methods

    func loginViewShowingLoggedInUser(loginView : FBLoginView!) {

                println("Start Fetched")
                var friendsRequest : FBRequest = FBRequest.requestForMyFriends()
                friendsRequest.startWithCompletionHandler{(connection:FBRequestConnection!, result:AnyObject!, error:NSError!) -> Void in
                    var resultdict = result as NSDictionary
                    println("Result Dict: \(resultdict)")
                    var Data : NSArray = resultdict.objectForKey("data") as NSArray
                    self.createFriendsInfo(Data)
                    println("Perform \(self.friendNames.count) \(self.friendPics.count) ")
                    self.performSegueWithIdentifier("toFriendList", sender: self)
                    println("Perform \(self.friendNames.count) \(self.friendPics.count) ")
        //
                }

        //self.performSegueWithIdentifier("toFriendList", sender: self)

    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func loginViewFetchedUserInfo(loginView : FBLoginView!, user: FBGraphUser) {
    }

    func loginViewShowingLoggedOutUser(loginView : FBLoginView!) {
        println("User Logged Out")
        self.friendNames = []
        self.friendPics = []
        println("Logout \(self.friendNames.count) \(self.friendPics.count) ")
    }

    func loginView(loginView : FBLoginView!, handleError:NSError) {
        println("Error: \(handleError.localizedDescription)")
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if((segue.identifier == "toFriendList" ) && (self.friendNames.count > 0))
        {
            var fl : friendList = segue.destinationViewController as friendList
            println("Prepare \(self.friendNames.count) \(self.friendPics.count) ")
            fl.name1 = self.friendNames
            fl.profilepics1 = self.friendPics
        }

    }






}

Answer 1

createFriendsInfo中的for循环上限错误；通常是 0..<data.count。事实上，

for i in 0...data.count {
  let valueDict : NSDictionary = data[i] as NSDictionary
  // ...

将在 i == data.count 时 'fail'。

但是，至于控制流，friendsRequest 完成处理程序肯定不会运行在主队列上。这意味着 performSegueWithIdentifier 将 'get lost'。将您的代码更改为：

func loginViewShowingLoggedInUser(loginView : FBLoginView!) {
  println("Start Fetched")
  var friendsRequest : FBRequest = FBRequest.requestForMyFriends()

  friendsRequest.startWithCompletionHandler{
      (connection:FBRequestConnection!, result:AnyObject!, error:NSError!) -> Void in
    var resultdict = result as NSDictionary
    println("Result Dict: \(resultdict)")
    var Data : NSArray = resultdict.objectForKey("data") as NSArray
    self.createFriendsInfo(Data)
    println("Perform \(self.friendNames.count) \(self.friendPics.count) ")
    dispatch_async(dispatch_get_main_queue()) {
      self.performSegueWithIdentifier("toFriendList", sender: self)
      println("Perform \(self.friendNames.count) \(self.friendPics.count) ")
      //
    }
  }
}

必须在主队列上执行所有 UI 操作。

请注意，您可能需要在 dispatch_async 的闭包中将 self 声明为 unowned（我忘记了当前的 Swift 状态）

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