为什么我不能在字符串上使用 write(toFile: ) 属性？

Question

我正在学习一个用早期版本的 Swift 编写的教程，它教我如何在 Swift3 中读取/写入 .txt 文件。到目前为止，Xcode 一直做得很好，可以让我知道何时使用旧语法，并为我将其更改为最新语法。但是，我遇到了一些适用于旧版本 Swift 的东西，但不是当前版本。

class ViewController: UIViewController {

    // MARK: Properties

    @IBOutlet weak var monthToEditTextField: UITextField!
    @IBOutlet weak var bedTimeTextField: UITextField!
    @IBOutlet weak var wakeTimeTextField: UITextField!
    @IBOutlet weak var theLabel: UILabel!

    @IBAction func saveButton(_ sender: UIButton)
    {
        var theMonth = monthToEditTextField.text
        var bedTime = bedTimeTextField.text
        var wakeTime = wakeTimeTextField.text

        var stringForTXTFile = "The user's info is: \(theMonth), \(bedTime), \(wakeTime)"

        let fileManager = FileManager.default

        if (!fileManager.fileExists(atPath: filePath))
        {
            var writeError: NSError?
            let fileToBeWritten = stringForTXTFile.write(toFile: // This is where the problem is
        }   
    }

当我输入时

stringForTXTFile.write

我收到此错误框

我需要做什么才能使用“write”属性？

Answer 1

在 Swift3 中写入文件不再返回 Bool。它抛出，所以只需删除let fileToBeWritten = 并使用do try catch error 处理。如果操作成功则需要运行的任何代码都需要放在 do try 大括号内。您还可以使用guard 来解开您的文本字段可选字符串。试试这样：

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var monthToEditTextField: UITextField!
    @IBOutlet weak var bedTimeTextField: UITextField!
    @IBOutlet weak var wakeTimeTextField: UITextField!
    @IBOutlet weak var theLabel: UILabel!
    let fileURL = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false).appendingPathComponent("textFile.txt")
    override func viewDidLoad() {
        super.viewDidLoad()
        // 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.
    }
    @IBAction func save(_ sender: UIButton) {
        guard
            let theMonth = monthToEditTextField.text,
            let bedTime = bedTimeTextField.text,
            let wakeTime = wakeTimeTextField.text
            else { return }

        let stringForTXTFile = "The user's info is: \(theMonth), \(bedTime), \(wakeTime)"
            do {
                try stringForTXTFile.write(toFile: fileURL.path, atomically: true, encoding: .utf8)
                // place code to be executed here if write was successful
            } catch {
                print(error.localizedDescription)
            }
    }

    @IBAction func load(_ sender: UIButton) {
        do {
            theLabel.text = try String(contentsOf: fileURL)
        } catch {
            print(error.localizedDescription)
        }
    }
}