在Swift中向文本文件追加文本或数据
我已经读过了 我需要将数据(字符串)附加到文本文件的末尾。在Swift中向文本文件追加文本或数据,swift,append,text-files,Swift,Append,Text Files,我已经读过了 我需要将数据(字符串)附加到文本文件的末尾。 一种显而易见的方法是从磁盘读取文件,并将字符串附加到文件末尾,然后将其写回,但这并不高效,特别是当您处理大型文件时,并且经常在磁盘中执行此操作 所以问题是“如何将字符串附加到文本文件的末尾,而不读取文件并将整个内容写回” 到目前为止,我已经: let dir:NSURL = NSFileManager.defaultManager().URLsForDirectory(NSSearchPathDirectory.CachesDi
一种显而易见的方法是从磁盘读取文件,并将字符串附加到文件末尾,然后将其写回,但这并不高效,特别是当您处理大型文件时,并且经常在磁盘中执行此操作 所以问题是“如何将字符串附加到文本文件的末尾,而不读取文件并将整个内容写回” 到目前为止,我已经:
let dir:NSURL = NSFileManager.defaultManager().URLsForDirectory(NSSearchPathDirectory.CachesDirectory, inDomains: NSSearchPathDomainMask.UserDomainMask).last as NSURL
let fileurl = dir.URLByAppendingPathComponent("log.txt")
var err:NSError?
// until we find a way to append stuff to files
if let current_content_of_file = NSString(contentsOfURL: fileurl, encoding: NSUTF8StringEncoding, error: &err) {
"\(current_content_of_file)\n\(NSDate()) -> \(object)".writeToURL(fileurl, atomically: true, encoding: NSUTF8StringEncoding, error: &err)
}else {
"\(NSDate()) -> \(object)".writeToURL(fileurl, atomically: true, encoding: NSUTF8StringEncoding, error: &err)
}
if err != nil{
println("CANNOT LOG: \(err)")
}
您应该使用NSFileHandle,它可以
下面是Swift 2的一个版本,它对字符串和NSData使用扩展方法
//: Playground - noun: a place where people can play
import UIKit
extension String {
func appendLineToURL(fileURL: NSURL) throws {
try self.stringByAppendingString("\n").appendToURL(fileURL)
}
func appendToURL(fileURL: NSURL) throws {
let data = self.dataUsingEncoding(NSUTF8StringEncoding)!
try data.appendToURL(fileURL)
}
}
extension NSData {
func appendToURL(fileURL: NSURL) throws {
if let fileHandle = try? NSFileHandle(forWritingToURL: fileURL) {
defer {
fileHandle.closeFile()
}
fileHandle.seekToEndOfFile()
fileHandle.writeData(self)
}
else {
try writeToURL(fileURL, options: .DataWritingAtomic)
}
}
}
// Test
do {
let url = NSURL(fileURLWithPath: "test.log")
try "Test \(NSDate())".appendLineToURL(url)
let result = try String(contentsOfURL: url)
}
catch {
print("Could not write to file")
}
下面是对Swift 3.0中PointZeroTwo答案的更新,其中有一个提示-在操场上使用简单的文件路径进行测试是可行的,但在我的实际应用中,我需要使用.documentDirectory(或您选择用于读写的任何目录-确保它在整个应用程序中保持一致)来构建URL:
谢谢零点二。更新:我写了一篇关于这一点的博客文章,你可以找到强> 为了保持快速,下面是一个使用默认实现的
FileWriter
协议的示例(撰写本文时为Swift 4.1):
- 要使用它,请让您的实体(类、结构、枚举)符合此协议,并调用write函数(仅供参考,它会抛出!)
- 写入文档目录
- 如果文件存在,将附加到文本文件
- 如果文本文件不存在,将创建一个新文件
- 注意:这仅适用于文本。您可以执行类似于写入/追加
数据的操作
import Foundation enum FileWriteError: Error { case directoryDoesntExist case convertToDataIssue } protocol FileWriter { var fileName: String { get } func write(_ text: String) throws } extension FileWriter { var fileName: String { return "File.txt" } func write(_ text: String) throws { guard let dir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { throw FileWriteError.directoryDoesntExist } let encoding = String.Encoding.utf8 guard let data = text.data(using: encoding) else { throw FileWriteError.convertToDataIssue } let fileUrl = dir.appendingPathComponent(fileName) if let fileHandle = FileHandle(forWritingAtPath: fileUrl.path) { fileHandle.seekToEndOfFile() fileHandle.write(data) } else { try text.write(to: fileUrl, atomically: false, encoding: encoding) } } }
- 以保持@PointZero-Two的精神。
这里是他的Swift 4.1代码的更新
extension String {
func appendLine(to url: URL) throws {
try self.appending("\n").append(to: url)
}
func append(to url: URL) throws {
let data = self.data(using: String.Encoding.utf8)
try data?.append(to: url)
}
}
extension Data {
func append(to url: URL) throws {
if let fileHandle = try? FileHandle(forWritingTo: url) {
defer {
fileHandle.closeFile()
}
fileHandle.seekToEndOfFile()
fileHandle.write(self)
} else {
try write(to: url)
}
}
}
下面是一种以更高效的方式更新文件的方法
let monkeyLine = "\nAdding a A variation over some of the posted answers, with following characteristics:
- based on Swift 5
- accessible as a static function
- appends new entries to the end of the file, if it exists
- creates the file, if it doesn't exist
- no cast to NS objects (more Swiftly)
- fails silently if the text cannot be encoded or the path does not exist
class Logger {
static var logFile: URL? {
guard let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return nil }
let formatter = DateFormatter()
formatter.dateFormat = "dd-MM-yyyy"
let dateString = formatter.string(from: Date())
let fileName = "\(dateString).log"
return documentsDirectory.appendingPathComponent(fileName)
}
static func log(_ message: String) {
guard let logFile = logFile else {
return
}
let formatter = DateFormatter()
formatter.dateFormat = "HH:mm:ss"
let timestamp = formatter.string(from: Date())
guard let data = (timestamp + ": " + message + "\n").data(using: String.Encoding.utf8) else { return }
if FileManager.default.fileExists(atPath: logFile.path) {
if let fileHandle = try? FileHandle(forWritingTo: logFile) {
fileHandle.seekToEndOfFile()
fileHandle.write(data)
fileHandle.closeFile()
}
} else {
try? data.write(to: logFile, options: .atomicWrite)
}
}
}
let monkeyLine=“\n在一些发布的答案上添加一个变体,具有以下特征:
- 基于Swift 5
- 可作为静态函数访问
- 将新条目追加到文件末尾(如果存在)
- 如果文件不存在,则创建该文件
- 不强制转换到NS对象(更快)
- 如果无法对文本进行编码或路径不存在,则以静默方式失败
如果您只需单击Xcode中带有白点的红色小圆圈,您会惊讶地发现将其转换为swift 3是多么容易。我正在尝试使用它,但我不知道如何做到这一点……”让您的实体(类、结构、枚举)符合此协议并调用写函数(仅供参考,它抛出!)“。我实际上如何调用它来保存VC中文本视图中的文本?这将两个概念联系在一起:符合协议&使用协议扩展来提供默认功能。首先,您的实体应该符合协议(例如,类MyClass:FileWriter)。现在,由于在FileWriter
协议上有一个协议要求的默认实现扩展,因此您的实体MyClass在本例中免费获得写入功能!因此,您可以在MyClass的实例上调用该函数。(例如,让myClassInstance=MyClass();试试!myClassInstance.write(“hello”))。此外,如果您想获得更详细的示例说明,请查看我的博客帖子,我在上面的回答中添加了一个链接:)。@John你是什么意思?您好@atineoSE在FileManager被否决后,您有什么关于如何使用的信息吗?看起来像var writeabilityHandler:((FileHandle)->Void)?是异步版本,工作非常出色。谢谢
extension String {
func appendLine(to url: URL) throws {
try self.appending("\n").append(to: url)
}
func append(to url: URL) throws {
let data = self.data(using: String.Encoding.utf8)
try data?.append(to: url)
}
}
extension Data {
func append(to url: URL) throws {
if let fileHandle = try? FileHandle(forWritingTo: url) {
defer {
fileHandle.closeFile()
}
fileHandle.seekToEndOfFile()
fileHandle.write(self)
} else {
try write(to: url)
}
}
}
let monkeyLine = "\nAdding a A variation over some of the posted answers, with following characteristics:
- based on Swift 5
- accessible as a static function
- appends new entries to the end of the file, if it exists
- creates the file, if it doesn't exist
- no cast to NS objects (more Swiftly)
- fails silently if the text cannot be encoded or the path does not exist
class Logger {
static var logFile: URL? {
guard let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return nil }
let formatter = DateFormatter()
formatter.dateFormat = "dd-MM-yyyy"
let dateString = formatter.string(from: Date())
let fileName = "\(dateString).log"
return documentsDirectory.appendingPathComponent(fileName)
}
static func log(_ message: String) {
guard let logFile = logFile else {
return
}
let formatter = DateFormatter()
formatter.dateFormat = "HH:mm:ss"
let timestamp = formatter.string(from: Date())
guard let data = (timestamp + ": " + message + "\n").data(using: String.Encoding.utf8) else { return }
if FileManager.default.fileExists(atPath: logFile.path) {
if let fileHandle = try? FileHandle(forWritingTo: logFile) {
fileHandle.seekToEndOfFile()
fileHandle.write(data)
fileHandle.closeFile()
}
} else {
try? data.write(to: logFile, options: .atomicWrite)
}
}
}