如何打开文件并在其中附加一个字符串，swift

Question

I am trying to append a string into text file. I am using the following code.

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
}

this does not append the string to file. Even if I call this function repeatedly.

Answer 1

If you want to be able to control whether to append or not, consider using OutputStream . For example:

SWIFT 3

let fileURL = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false)
    .appendingPathComponent("votes.txt")

if let outputStream = OutputStream(url: fileURL, append: true) {
    outputStream.open()
    let text = "some text\n"
    let bytesWritten = outputStream.write(text)
    if bytesWritten < 0 { print("write failure") }
    outputStream.close()
} else {
    print("Unable to open file")
}

By the way, this is an extension that lets you easily write a String to an OutputStream :

extension OutputStream {

    /// 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`.
    ///
    /// - returns:                         Return total number of bytes written upon success. Return `-1` upon failure.

    func write(_ string: String, encoding: String.Encoding = .utf8, allowLossyConversion: Bool = false) -> Int {

        if let data = string.data(using: encoding, allowLossyConversion: allowLossyConversion) {
            return data.withUnsafeBytes { (bytes: UnsafePointer<UInt8>) -> Int in
                var pointer = bytes
                var bytesRemaining = data.count
                var totalBytesWritten = 0

                while bytesRemaining > 0 {
                    let bytesWritten = self.write(pointer, maxLength: bytesRemaining)
                    if bytesWritten < 0 {
                        return -1
                    }

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

                return totalBytesWritten
            }
        }

        return -1
    }

}

Or, in Swift 2 use NSOutputStream :

let documents = try! NSFileManager.defaultManager().URLForDirectory(.DocumentDirectory, inDomain: .UserDomainMask, appropriateForURL: nil, create: false)
let path = documents.URLByAppendingPathComponent("votes").path!

if let outputStream = NSOutputStream(toFileAtPath: path, append: true) {
    outputStream.open()
    let text = "some text"
    outputStream.write(text)

    outputStream.close()
} else {
    print("Unable to open file")
}

And

extension NSOutputStream {

    /// Write `String` to `NSOutputStream`
    ///
    /// - parameter string:                The string to write.
    /// - parameter encoding:              The NSStringEncoding 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`.
    ///
    /// - returns:                         Return total number of bytes written upon success. Return -1 upon failure.

    func write(string: String, encoding: NSStringEncoding = NSUTF8StringEncoding, allowLossyConversion: Bool = false) -> Int {
        if let data = string.dataUsingEncoding(encoding, allowLossyConversion: allowLossyConversion) {
            var bytes = UnsafePointer<UInt8>(data.bytes)
            var bytesRemaining = data.length
            var totalBytesWritten = 0

            while bytesRemaining > 0 {
                let bytesWritten = self.write(bytes, maxLength: bytesRemaining)
                if bytesWritten < 0 {
                    return -1
                }

                bytesRemaining -= bytesWritten
                bytes += bytesWritten
                totalBytesWritten += bytesWritten
            }

            return totalBytesWritten
        }

        return -1
    }

}

Answer 2

You can also useFileHandle to append String to your text file. If you just want to append your string the end of your text file just callseekToEndOfFile method, write your string data and just close it when you are done:

---

FileHandle usage Swift 3 or Later

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

Please check the below code as its working for me. Just Add the code as it is:

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

Check the reading part.

The method cotentsOfFile: is a method of NSString class. And you have use it wrong way.

So replace this line

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

Here you have to use NSString instead of String class.

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

Answer 5

A simple solution that works for me. UPDATE, it looks like I must have gotten this from here, so credit where credit is due: Append text or data to text file in Swift

Usage:

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

Code:

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)
        }
    }
}