Question

我有两个数组：pointHistory和dateHistory。我也有NSTimer，当计时器用完时，会调用其动作。在该操作中，我将Int追加到pointHistory，将当前日期追加到string到dateHistory。这是计时器操作：

 func timerAction() {
    let stepperValue = Int(stepper.value)
    employee.numberOfPoints = stepperValue

    networking.saveEmployee(employee, completion: { (error) -> Void in
        if error != nil {
            let alert = UIAlertController(title: "Error", message: "There was an error updating \(self.employee.name)'s points", preferredStyle: .Alert)
            let alertAction = UIAlertAction(title: "Ok", style: .Cancel, handler: nil)
            alert.addAction(alertAction)
            self.presentViewController(alert, animated: true, completion: nil)
        }
    })

    var dateFormatter = NSDateFormatter()
    dateFormatter.dateFormat = "MM-dd-yyyy"
    dateFormatter.timeZone = NSTimeZone.localTimeZone()

    var date = NSDate()
    var dateString = dateFormatter.stringFromDate(date)

    //APPENDING HERE
    self.pointHistory.append(self.employee.numberOfPoints)
    self.dateHistory.append(dateString)
}

但是，当视图加载时，这两个数组会将自身重置为空。这是我的viewDidLoad方法：

override func viewDidLoad() {
    super.viewDidLoad()

    self.view.backgroundColor = UIColor.whiteColor()
    self.title = employee.name


    editBarButtonItem = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.Edit, target: self, action: Selector("edit"))
    if let font = UIFont(name: "Avenir", size: 18) {
        editBarButtonItem.setTitleTextAttributes([NSFontAttributeName: font], forState: UIControlState.Normal)
    }
    self.navigationItem.rightBarButtonItem = editBarButtonItem

    if let font = UIFont(name: "Avenir", size: 17) {
        UIBarButtonItem.appearance().setTitleTextAttributes([NSFontAttributeName: font], forState: UIControlState.Normal)
    }

    self.addScrollView()
    self.addProfilePicture()
    self.addUIElements()
    self.addLineChart()

    setChart(dateHistory, yVals: pointHistory)

}

dateHistory和pointHistory的重点是我为我的应用添加折线图，所有数据都存储在这些数组中。这是老挝为什么你看到一个setChart函数。对于lineChart，我使用的是iOS图表框架。这是setChart函数的实际主体，因为它在viewDidLoad中调用：

 func setChart(xVals: [String], yVals: [Int]) {
    var dataEntries = [ChartDataEntry]()

    for i in 0..<xVals.count {
        let dataEntry = ChartDataEntry(value: Double(yVals[i]), xIndex: i)
        dataEntries.append(dataEntry)
    }

    let lineChartDataSet = LineChartDataSet(yVals: dataEntries, label: "Number of Points")
    let lineChartData = LineChartData(xVals: xVals, dataSet: lineChartDataSet)
    lineChart.data = lineChartData
}

最后，为了提供更多信息，重置数组的原因可能是因为我实现了viewWillAppear函数。这是：

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
    self.refreshView()
}

以下是refreshView功能：

 func refreshView() {
    self.networking.findEmployeeForLoggedInUser { (array, error) -> Void in
        if error != nil {
            let alert = UIAlertController(title: "Error", message: "\(error)", preferredStyle: .Alert)
            let alertAction = UIAlertAction(title: "Ok", style: .Cancel, handler: nil)
            alert.addAction(alertAction)
            self.presentViewController(alert, animated: true, completion: nil)
        } else {
            dispatch_async(dispatch_get_main_queue(), { () -> Void in
                self.nameLabel.text = self.employee.name
                self.title = self.employee.name
                self.roleLabel.text = self.employee.jobDesc
                self.educationLabel.text = self.employee.education
                self.birthdayLabel.text = self.employee.birthday
                self.commentaryTextView.text = self.employee.commentary
                self.emailTextView.text = self.employee.email
            })
        }
    }

    self.networking.fetchImageForEmployee(employee, completion: { (error, image) -> Void in
        self.imageActInd.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.White
        self.image.addSubview(self.imageActInd)

        self.imageActInd.setTranslatesAutoresizingMaskIntoConstraints(false)
        self.view.addConstraint(NSLayoutConstraint(item: self.imageActInd, attribute: .CenterX, relatedBy: .Equal, toItem: self.image, attribute: .CenterX, multiplier: 1.0, constant: 0.0))
        self.view.addConstraint(NSLayoutConstraint(item: self.imageActInd, attribute: .CenterY, relatedBy: .Equal, toItem: self.image, attribute: .CenterY, multiplier: 1.0, constant: 0.0))

        self.imageActInd.startAnimating()
        self.image.alpha = 0.5

        if error != nil {
            dispatch_async(dispatch_get_main_queue(), { () -> Void in
                self.imageActInd.stopAnimating()
                self.image.alpha = 1.0
            })

            let alert = UIAlertController(title: "Error", message: "\(error!)", preferredStyle: .Alert)
            let alertAction = UIAlertAction(title: "Ok", style: .Cancel, handler: nil)
            alert.addAction(alertAction)
            self.presentViewController(alert, animated: true, completion: nil)
        } else {
            dispatch_async(dispatch_get_main_queue(), { () -> Void in
                self.imageActInd.stopAnimating()
                self.image.alpha = 1.0
                self.image.image = image
            })
        }
    })
}

我不知道为什么这些数组被重置为空。我做错了什么？

Answer 1

[这假设所有这些代码都在单个UIViewController实例中运行。]

我认为您误解了UIViewController生命周期的某些方面。在你的应用程序的启动过程中，viewDidLoad()仅被调用一次，当时没有任何UI可见，没有任何组件布局，也没有定时器被给予机会开始。除非您此时从持久性存储（磁盘;数据库;等）中加载数据，否则您的数组将具有从重写构造函数（如果有的话）设置的值，否则将具有从中设置的值他们的类级声明初始化器。

你什么时候开始NSTimer，你什么时候开始关注它？

您使用println()或调试断点来教自己真实的事件序列吗？

我还要补充一点，你在主线程上做了一些UI代码，这是一个很大的禁忌。警报的显示必须遵循与非错误UI路径相同的dispatch模式。

Swift数组重置自身

1 个答案: