NSUserDefaults 在 Swift 中不能与 UITableView 一起使用

Question

我对 Swift 比较陌生，正在制作一个基本的家庭作业日记应用程序。到目前为止，我所拥有的是嵌入在导航控制器中的 UITableView，该导航控制器嵌入在标签栏控制器中。我已经成功地实现了拉动刷新，在 UIAlertView 中添加数据并在刷新后用这些数据填充表。我需要这个应用程序的持久数据，我听说 NSUserDefaults 是最好的方法，但它对我不起作用。我可以看到它正在添加到 NSUserDefaults，但在我关闭并重新打开应用程序后，它似乎没有重新出现在 UITableView 中。有什么建议？我的代码如下。另外，要将这些数据放到网上，有没有办法将 Google 表格用作我的应用的在线数据库？

import UIKit
var classesData = [String]()
var teachersData = [String]()
let defaults = NSUserDefaults.standardUserDefaults()
var tableData1 = defaults.valueForKey("classesData") as! NSArray
var tableData2 = defaults.valueForKey("teachersData") as! NSArray

class ClassesList: UIViewController, UITableViewDelegate, UITableViewDataSource, UIPopoverPresentationControllerDelegate {
lazy var refreshControl: UIRefreshControl = {
    let refreshControl = UIRefreshControl()
    refreshControl.addTarget(self, action: "handleRefresh:", forControlEvents: UIControlEvents.ValueChanged)

    return refreshControl
}()
@IBOutlet weak var tableView: UITableView!
@IBAction func addClass(sender: AnyObject) {
    var subjectTextField: UITextField?
    var teacherTextField: UITextField?
    let alertController = UIAlertController(title: "Add Class", message: "Please input the name of the subject and the teaceher", preferredStyle: .Alert)
    let done = UIAlertAction(title: "Done", style: .Default, handler: { (action) -> Void in
        classesData.append(subjectTextField!.text!)
        teachersData.append(teacherTextField!.text!)
        print(classesData)
        print(teachersData)
    })
    let cancel = UIAlertAction(title: "Cancel", style: .Cancel) { (action) -> Void in
    }
    alertController.addAction(done)
    alertController.addAction(cancel)
    alertController.addTextFieldWithConfigurationHandler { (textField) -> Void in
        // Enter the textfiled customization code here.
        subjectTextField = textField
        subjectTextField?.placeholder = "Subject"
    }
    alertController.addTextFieldWithConfigurationHandler { (textField) -> Void in
        // Enter the textfiled customization code here.
        teacherTextField = textField
        teacherTextField?.placeholder = "Teacher"
    }
    presentViewController(alertController, animated: true, completion: nil)

}

override func viewDidLoad() {
    super.viewDidLoad()
    self.tableView.registerClass(UITableViewCell.self, forCellReuseIdentifier: "classCell")
    self.tableView.addSubview(self.refreshControl)


    // Do any additional setup after loading the view, typically from a nib.
}

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

}
func handleRefresh(refreshControl: UIRefreshControl) {
    defaults.setValue(classesData, forKey: "classesData")
    defaults.setValue(teachersData, forKey: "teachersData")
    print(tableData1)
    defaults.synchronize()
    self.tableView.reloadData()
    refreshControl.endRefreshing()
}
func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    return 1
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return classesData.count
}

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    let cell:UITableViewCell = self.tableView.dequeueReusableCellWithIdentifier("classCell")! as UITableViewCell

    cell.textLabel?.text = (tableData1[indexPath.row] as? String)! + " , " + (tableData2[indexPath.row] as? String)!

    return cell
}

}

Answer 1

在启动时，您使用 tableData1 和 tableData2 来存储默认信息，但 classesData 和 teacherData 被初始化为空。当应用程序启动时，它会调用 numberOfRowsInSection 并返回 classesData.count，它是零。您遇到的另一个问题是您的应用程序将在第一次运行时崩溃，因为您使用空的 NSUserDefaults 数据对其进行初始化。重置 iOS 模拟器，然后运行您的应用程序，它会崩溃。您需要检查和处理来自此处介绍的 NSUserDefaults 的空数据：how to save and read array of array in NSUserdefaults in swift?

我建议如下： 1）删除 tableData1 和 tableData1 并在应用程序中的任何地方替换为 classesData 和 teacherData。 2) 创建一个名为 loadUserDefaults() 的新函数，该函数在 viewDidLoad 中调用，该函数在检查空 NSUserDefaults 数据时从 NSUserDefaults 加载数据。 3) 在handleRefresh() 中只保存数据，重新加载表格视图并结束刷新。有了这些建议，工作代码如下。

import UIKit
var classesData = [String]()
var teachersData = [String]()
let defaults = NSUserDefaults.standardUserDefaults()

class ClassesList: UIViewController, UITableViewDelegate, UITableViewDataSource, UIPopoverPresentationControllerDelegate {
    lazy var refreshControl: UIRefreshControl = {
        let refreshControl = UIRefreshControl()
        refreshControl.addTarget(self, action: "handleRefresh:", forControlEvents: UIControlEvents.ValueChanged)

        return refreshControl
    }()
    @IBOutlet weak var tableView: UITableView!
    @IBAction func addClass(sender: AnyObject) {
        var subjectTextField: UITextField?
        var teacherTextField: UITextField?
        let alertController = UIAlertController(title: "Add Class", message: "Please input the name of the subject and the teaceher", preferredStyle: .Alert)
        let done = UIAlertAction(title: "Done", style: .Default, handler: { (action) -> Void in
            classesData.append(subjectTextField!.text!)
            teachersData.append(teacherTextField!.text!)
        })
        let cancel = UIAlertAction(title: "Cancel", style: .Cancel) { (action) -> Void in
        }
        alertController.addAction(done)
        alertController.addAction(cancel)
        alertController.addTextFieldWithConfigurationHandler { (textField) -> Void in
            // Enter the textfiled customization code here.
            subjectTextField = textField
            subjectTextField?.placeholder = "Subject"
        }
        alertController.addTextFieldWithConfigurationHandler { (textField) -> Void in
            // Enter the textfiled customization code here.
            teacherTextField = textField
            teacherTextField?.placeholder = "Teacher"
        }
        presentViewController(alertController, animated: true, completion: nil)

    }

    override func viewDidLoad() {
        super.viewDidLoad()
        self.tableView.registerClass(UITableViewCell.self, forCellReuseIdentifier: "classCell")
        self.tableView.addSubview(self.refreshControl)
        loadUserDefaults()
    }

    func handleRefresh(refreshControl: UIRefreshControl) {
        defaults.setValue(classesData, forKey: "classesData")
        defaults.setValue(teachersData, forKey: "teachersData")
        defaults.synchronize()
        self.tableView.reloadData()
        refreshControl.endRefreshing()
    }

    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return classesData.count
    }

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell:UITableViewCell = self.tableView.dequeueReusableCellWithIdentifier("classCell")! as UITableViewCell
        cell.textLabel?.text = (classesData[indexPath.row] as? String)! + " , " + (teachersData[indexPath.row] as? String)!

        return cell
    }

    func loadUserDefaults() {
        if let tempClassArray = defaults.valueForKey("classesData") {
            classesData = tempClassArray as! [String]
        }

        if let tempTeacherArray = defaults.valueForKey("classesData") {
            teachersData = tempTeacherArray as! [String]
        }
    }

}