如何快速打开文件并在其中附加一个字符串

Question

我正在尝试将字符串附加到文本文件中。我正在使用以下代码。

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

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

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

这不会将字符串附加到文件中。即使我反复调用这个函数。

Answer 1

如果您希望能够控制是否追加，请考虑使用OutputStream。例如：

do {
    let fileURL = try FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false)
        .appendingPathComponent("votes.txt")
    
    guard let outputStream = OutputStream(url: fileURL, append: true) else {
        print("Unable to open file")
        return
    }

    outputStream.open()
    let text = "some text\n"
    try outputStream.write(text)
    outputStream.close()
} catch {
    print(error)
}

顺便说一句，这是一个扩展，可让您轻松地将String（或Data）写入OutputStream：

extension OutputStream {
    enum OutputStreamError: Error {
        case stringConversionFailure
        case bufferFailure
        case writeFailure
    }

    /// Write `String` to `OutputStream`
    ///
    /// - parameter string:                The `String` to write.
    /// - parameter encoding:              The `String.Encoding` to use when writing the string. This will default to `.utf8`.
    /// - parameter allowLossyConversion:  Whether to permit lossy conversion when writing the string. Defaults to `false`.

    func write(_ string: String, encoding: String.Encoding = .utf8, allowLossyConversion: Bool = false) throws {
        guard let data = string.data(using: encoding, allowLossyConversion: allowLossyConversion) else {
            throw OutputStreamError.stringConversionFailure
        }
        try write(data)
    }

    /// Write `Data` to `OutputStream`
    ///
    /// - parameter data:                  The `Data` to write.

    func write(_ data: Data) throws {
        try data.withUnsafeBytes { (buffer: UnsafeRawBufferPointer) throws in
            guard var pointer = buffer.baseAddress?.assumingMemoryBound(to: UInt8.self) else {
                throw OutputStreamError.bufferFailure
            }

            var bytesRemaining = buffer.count

            while bytesRemaining > 0 {
                let bytesWritten = write(pointer, maxLength: bytesRemaining)
                if bytesWritten < 0 {
                    throw OutputStreamError.writeFailure
                }

                bytesRemaining -= bytesWritten
                pointer += bytesWritten
            }
        }
    }
}

对于 Swift 2 版本，请参阅此答案的 previous revision。

Answer 2

您也可以使用FileHandle 将字符串附加到您的文本文件中。如果您只想将字符串附加到文本文件的末尾，只需调用 seekToEndOfFile 方法，写入字符串数据并在完成后将其关闭：

---

FileHandle 使用 Swift 3 或更高版本

let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!

// create a new text file at your documents directory or use an existing text file resource url
let fileURL = documentsDirectory.appendingPathComponent("simpleText.txt")
do {
    try Data("Hello World\n".utf8).write(to: fileURL)
} catch {
    print(error) 
}
// open your text file and set the file pointer at the end of it
do {
    let fileHandle = try FileHandle(forWritingTo: fileURL)
    fileHandle.seekToEndOfFile()
    // convert your string to data or load it from another resource
    let str = "Line 1\nLine 2\n"
    let textData = Data(str.utf8)
    // append your text to your text file
    fileHandle.write(textData)
    // close it when done
    fileHandle.closeFile()
    // testing/reading the file edited
    if let text = try? String(contentsOf: fileURL, encoding: .utf8) {
        print(text)  // "Hello World\nLine 1\nLine 2\n\n"
    }
} catch {
    print(error)
}

Answer 3

请检查以下代码是否适合我。只需按原样添加代码：

let theDocumetFolderSavingFiles = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as String
let filePath = "/theUserData.txt"
let thePathToFile = theDocumetFolderSavingFiles.stringByAppendingString(filePath)
let theFileManager = NSFileManager.defaultManager()

if(theFileManager.fileExistsAtPath(thePathToFile)){

        do {

            let stringToStore = "Hello working fine"
            try stringToStore.writeToFile(thePathToFile, atomically: true, encoding: NSUTF8StringEncoding)

        }catch let error as NSError {
            print("we are geting exception\(error.domain)")
        }

        do{
            let fetchResult = try NSString(contentsOfFile: thePathToFile, encoding: NSUTF8StringEncoding)
            print("The Result is:-- \(fetchResult)")
        }catch let errorFound as NSError{
            print("\(errorFound)")
        }

    }else
    {
        // Code to Delete file if existing
        do{
            try theFileManager.removeItemAtPath(thePathToFile)
        }catch let erorFound as NSError{
            print(erorFound)
        }
    }

Answer 4

检查阅读部分。

方法cotentsOfFile:是NSString类的方法。而且你用错了。

所以替换这一行

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

这里你必须使用NSString 而不是String 类。

let text2 = NSString(contentsOfFile: path, encoding: NSUTF8StringEncoding, error: nil)

Answer 5

一个适合我的简单解决方案。更新，看起来我一定是从这里得到的，所以信用到期： Append text or data to text file in Swift

用法：

"Hello, world".appendToURL(fileURL: url)

代码：

extension String {
    func appendToURL(fileURL: URL) throws {
        let data = self.data(using: String.Encoding.utf8)!
        try data.append(fileURL: fileURL)
    }
}

extension Data {
    func append(fileURL: URL) throws {
        if let fileHandle = FileHandle(forWritingAtPath: fileURL.path) {
            defer {
                fileHandle.closeFile()
            }
            fileHandle.seekToEndOfFile()
            fileHandle.write(self)
        }
        else {
            try write(to: fileURL, options: .atomic)
        }
    }
}