Question

我的代码有一个奇怪的错误我无法解决。

我使用swift和parse构建了一个应用程序。您登录，并被带到表视图的主页面。现在，如果您已登录，并离开并返回应用程序，一切都很好，花花公子。

但是，当我退出时，用户将被带回登录屏幕。现在，如果用户离开应用程序，但又返回，则应用程序崩溃时会在展开可选值时意外发现nil错误。

对我来说没有任何意义。当应用程序从头开始新鲜时，用户设置为nil，然后用户登录并且一切都很酷。当您注销时，用户将被设置回nil并进入登录屏幕。如果你恢复应用程序，请崩溃。

这是我注销用户的问题吗？

相关代码张贴在下面..

在登录页面上：

@IBAction func loginButton(sender: AnyObject) {
    //checks if there is a matching username with a matching password. if so, lets the user log in.



    PFUser.logInWithUsernameInBackground(username.text, password: userPassword.text) {
        (user: PFUser?, error: NSError?) -> Void in
        if user != nil {
            // Do stuff after successful login.
            //go to main table view
            //get current user
            //display current users locations
            println("login success")


            //shows home screen after successful login.
            self.performSegueWithIdentifier("showHomeFromLogin", sender: self)
        } else {
            // The login failed. Check error to see why.
            //display error?
            self.displayAlert("Login Failed", alertMessage: "Double check to make sure the username and password are correct.")
            println("login failed")
        }
    }

}


var activeField: UITextField?





override func viewDidLoad() {
    super.viewDidLoad()


    username.delegate = self
    userPassword.delegate = self

    registerForKeyboardNotifications()




    // Do any additional setup after loading the view.
    //setup so when we tap outside the edit, we close keyboard.
    var tap: UITapGestureRecognizer = UITapGestureRecognizer(target: self, action: "DismissKeyboard")
    view.addGestureRecognizer(tap)
}


override func viewDidAppear(animated: Bool) {
    if PFUser.currentUser() != nil {
        self.performSegueWithIdentifier("showHomeFromLogin", sender: self)
    }

}

在用户注销的主页上：

@IBAction func logoutButton(sender: AnyObject) {

    PFUser.logOut()
    var currentUser = PFUser.currentUser() // this will now be nil
    self.performSegueWithIdentifier("logoutSegue", sender: self)
}

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    NSNotificationCenter.defaultCenter().addObserver(self, selector: "launchSync", name: UIApplicationDidBecomeActiveNotification, object: nil)

    //setting table view datasource and delegate.
    self.tableView.dataSource = self
    self.tableView.delegate = self



    var currentUser = PFUser.currentUser()
    println(currentUser)

}

在这里突破我想在query.whereKey("User", equalTo:PFUser.currentUser()!)行：

func launchSync() {
    var query = PFQuery(className:"ParseLighthouse")
    query.whereKey("User", equalTo:PFUser.currentUser()!)
    query.findObjectsInBackgroundWithBlock {
        (objects: [AnyObject]?, error: NSError?) -> Void in

        if error == nil {
            // The find succeeded.
            println("Successfully retrieved \(objects!.count) lighthouses.")
            // Do something with the found objects
            if let light = objects as? [PFObject] {
                for object in light {
                    println(object.objectId)
                }
            }
            println(objects?.count)
            self.syncToLighthouse(objects!)
        } else {
            // Log details of the failure
            println("Error: \(error!) \(error!.userInfo!)")
        }
    }
}

此视图中的launchsync函数在我的主屏幕上显示方法。是否有可能在执行注销segue时，主视图控制器仍然在后台运行，所以当我恢复时，该代码无法找到用户现在将其设置回nil？

Answer 1

如果条件值有可能为零，则需要在使用之前检查条件。如果当前没有登录用户，PFUser.currentUser()将返回nil。当您强制用!打开此值时，您会收到异常。

您可以更改代码以有条件地解包值 -

func launchSync() {
    if let currentUser=PFUser.currentUser() {
        var query = PFQuery(className:"ParseLighthouse")
        query.whereKey("User", equalTo:currentUser)
        query.findObjectsInBackgroundWithBlock {
            (objects: [AnyObject]?, error: NSError?) -> Void in

            if error == nil {
                // The find succeeded.
                println("Successfully retrieved \(objects!.count) lighthouses.")
                // Do something with the found objects
                if let light = objects as? [PFObject] {
                    for object in light {
                        println(object.objectId)
                    }
                }
                println(objects?.count)
                self.syncToLighthouse(objects!)
            } else {
                // Log details of the failure
                println("Error: \(error!) \(error!.userInfo!)")
            }
        }
    } 
}

Answer 2

在以下一行

NSNotificationCenter.defaultCenter().addObserver(self, selector: "launchSync", name: UIApplicationDidBecomeActiveNotification, object: nil)

你说当应用程序变为活动状态时调用launchSync函数。

正如Paulw11所提到的，你在PFUser.currentUser()内强制展开（使用！），当用户退出时会返回nil。

您可以通过确保当前用户不是

来解决此问题

func launchSync() {
    if (PFUser.currentUser() != nil) {
        var query = PFQuery(className:"ParseLighthouse")
        query.whereKey("User", equalTo:PFUser.currentUser()!)
        query.findObjectsInBackgroundWithBlock {
            (objects: [AnyObject]?, error: NSError?) -> Void in

            if error == nil {
                // The find succeeded.
                println("Successfully retrieved \(objects!.count) lighthouses.")
                // Do something with the found objects
                if let light = objects as? [PFObject] {
                    for object in light {
                        println(object.objectId)
                    }
                }
                println(objects?.count)
                self.syncToLighthouse(objects!)
            } else {
                // Log details of the failure
                println("Error: \(error!) \(error!.userInfo!)")
            }
        }
    }
}

应用程序恢复后，当注销后，swift解析应用程序崩溃

2 个答案: