对于读写，您应该使用一个可写的位置，例如文档目录。下面的代码展示了如何读写一个简单的字符串。你可以在操场上测试。

斯威夫特3。X - 5.x

let file = "file.txt" //this is the file. we will write to and read from it

let text = "some text" //just a text

if let dir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {

    let fileURL = dir.appendingPathComponent(file)

    //writing
    do {
        try text.write(to: fileURL, atomically: false, encoding: .utf8)
    }
    catch {/* error handling here */}

    //reading
    do {
        let text2 = try String(contentsOf: fileURL, encoding: .utf8)
    }
    catch {/* error handling here */}
}

斯威夫特2.2

let file = "file.txt" //this is the file. we will write to and read from it

let text = "some text" //just a text

if let dir = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.AllDomainsMask, true).first {
    let path = NSURL(fileURLWithPath: dir).URLByAppendingPathComponent(file)

    //writing
    do {
        try text.writeToURL(path, atomically: false, encoding: NSUTF8StringEncoding)
    }
    catch {/* error handling here */}

    //reading
    do {
        let text2 = try NSString(contentsOfURL: path, encoding: NSUTF8StringEncoding)
    }
    catch {/* error handling here */}
}

快1.倍

let file = "file.txt"

if let dirs : [String] = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.AllDomainsMask, true) as? [String] {
    let dir = dirs[0] //documents directory
    let path = dir.stringByAppendingPathComponent(file);
    let text = "some text"

    //writing
    text.writeToFile(path, atomically: false, encoding: NSUTF8StringEncoding, error: nil);

    //reading
    let text2 = String(contentsOfFile: path, encoding: NSUTF8StringEncoding, error: nil)
}

新的更简单和推荐的方法: 苹果建议使用url进行文件处理，这里的其他解决方案似乎已被弃用(见下面的评论)。 下面是新的简单的读写URL的方法:

Swift 5+， 4和3.1

import Foundation  // Needed for those pasting into Playground

let fileName = "Test"
let dir = try? FileManager.default.url(for: .documentDirectory, 
      in: .userDomainMask, appropriateFor: nil, create: true)

guard let fileURL = dir?.appendingPathComponent(fileName).appendingPathExtension("txt") else {
    fatalError("Not able to create URL")
}
    
// Writing to the file named Test
let outString = "Write this text to the file"
do {
    try outString.write(to: fileURL, atomically: true, encoding: .utf8)
} catch {
    assertionFailure("Failed writing to URL: \(fileURL), Error: " + error.localizedDescription)
}
    
// Reading it back from the file
var inString = ""
do {
    inString = try String(contentsOf: fileURL)
} catch {
    assertionFailure("Failed reading from URL: \(fileURL), Error: " + error.localizedDescription)
}
print("Read from the file: \(inString)")

我只想给你们看第一部分，也就是阅读部分。以下是简单的阅读方法:

斯威夫特3:

let s = try String(contentsOfFile: Bundle.main.path(forResource: "myFile", ofType: "txt")!)

斯威夫特2:

let s = try! String(contentsOfFile: NSBundle.mainBundle().pathForResource("myFile", ofType: "txt")!)

对于我的txt文件是这样工作的:

let myFileURL = NSBundle.mainBundle().URLForResource("listacomuni", withExtension: "txt")!
let myText = try! String(contentsOfURL: myFileURL, encoding: NSISOLatin1StringEncoding)
print(String(myText))

我必须像这样重新编码:

let path = NSBundle.mainBundle().pathForResource("Output_5", ofType: "xml")
let text = try? NSString(contentsOfFile: path! as String, encoding: NSUTF8StringEncoding)
print(text)

这适用于Linux上的Swift 3.1.1:

import Foundation

let s = try! String(contentsOfFile: "yo", encoding: .utf8)