在Swift中逐行阅读文件/ URL [英] Read a file/URL line-by-line in Swift
问题描述
我正在尝试读取 NSURL 中提供的文件，并将其加载到一个数组中，其中用换行符<\\ c $ c> \\\
。
I am trying to read a file given in an NSURL and load it into an array, with items separated by a newline character \n.
以下是我迄今为止所做的工作：
Here is the way I've done it so far:
var possList: NSString? = NSString.stringWithContentsOfURL(filePath.URL) as? NSString
if var list = possList {
list = list.componentsSeparatedByString("\n") as NSString[]
return list
}
else {
//return empty list
}
我对此不满意几个原因。一，我正在处理大小从几千字节到数百MB的文件。你可以想象，使用字符串这个大的是缓慢和笨重的。其次，这在执行时冻结了UI - 再次不好。
I'm not very happy with this for a couple of reasons. One, I'm working with files that range from a few kilobytes to hundreds of MB in size. As you can imagine, working with strings this large is slow and unwieldy. Secondly, this freezes up the UI when it's executing--again, not good.
我已经研究了在一个单独的线程中运行这个代码，但是我已经有麻烦的，除此之外，它仍然不能解决处理巨大的字符串的问题。
I've looked into running this code in a separate thread, but I've been having trouble with that, and besides, it still doesn't solve the problem of dealing with huge strings.
我想做的是沿着以下伪代码：
What I'd like to do is something along the lines of the following pseudocode:
var aStreamReader = new StreamReader(from_file_or_url)
while aStreamReader.hasNextLine == true {
currentline = aStreamReader.nextLine()
list.addItem(currentline)
}
如何在Swift中完成这项工作？
有关我正在阅读的文件的一些注意事项： em>所有文件都由短小的（<255个字符）的字符串组成，由 \\\或
\r\\\。文件的长度范围从〜100行到超过5000万行。它们可能包含欧洲字符和/或带有重音的字符。
A few notes about the files I'm reading from: All files consist of short (<255 chars) strings separated by either \n or \r\n. The length of the files range from ~100 lines to over 50 million lines. They may contain European characters, and/or characters with accents.
推荐答案
（代码是用于Swift 2.2 / Xcode 7.3现在，如果有人需要，可以在编辑历史中找到较旧的版本。最后提供了Swift 3的更新版本。）
以下Swift代码受到各种答案
如何从NSFileHandle逐行读取数据？它以块的形式从文件中读取，并将完整的行转换为字符串。
The following Swift code is heavily inspired by the various answers to How to read data from NSFileHandle line by line?. It reads from the file in chunks, and converts complete lines to strings.
默认行分隔符（ \\\），字符串编码（UTF-8）和块大小（4096）可以使用可选参数设置
。
The default line delimiter (\n), string encoding (UTF-8) and chunk size (4096)
can be set with optional parameters.
class StreamReader {
let encoding : UInt
let chunkSize : Int
var fileHandle : NSFileHandle!
let buffer : NSMutableData!
let delimData : NSData!
var atEof : Bool = false
init?(path: String, delimiter: String = "\n", encoding : UInt = NSUTF8StringEncoding, chunkSize : Int = 4096) {
self.chunkSize = chunkSize
self.encoding = encoding
if let fileHandle = NSFileHandle(forReadingAtPath: path),
delimData = delimiter.dataUsingEncoding(encoding),
buffer = NSMutableData(capacity: chunkSize)
{
self.fileHandle = fileHandle
self.delimData = delimData
self.buffer = buffer
} else {
self.fileHandle = nil
self.delimData = nil
self.buffer = nil
return nil
}
}
deinit {
self.close()
}
/// Return next line, or nil on EOF.
func nextLine() -> String? {
precondition(fileHandle != nil, "Attempt to read from closed file")
if atEof {
return nil
}
// Read data chunks from file until a line delimiter is found:
var range = buffer.rangeOfData(delimData, options: [], range: NSMakeRange(0, buffer.length))
while range.location == NSNotFound {
let tmpData = fileHandle.readDataOfLength(chunkSize)
if tmpData.length == 0 {
// EOF or read error.
atEof = true
if buffer.length > 0 {
// Buffer contains last line in file (not terminated by delimiter).
let line = NSString(data: buffer, encoding: encoding)
buffer.length = 0
return line as String?
}
// No more lines.
return nil
}
buffer.appendData(tmpData)
range = buffer.rangeOfData(delimData, options: [], range: NSMakeRange(0, buffer.length))
}
// Convert complete line (excluding the delimiter) to a string:
let line = NSString(data: buffer.subdataWithRange(NSMakeRange(0, range.location)),
encoding: encoding)
// Remove line (and the delimiter) from the buffer:
buffer.replaceBytesInRange(NSMakeRange(0, range.location + range.length), withBytes: nil, length: 0)
return line as String?
}
/// Start reading from the beginning of file.
func rewind() -> Void {
fileHandle.seekToFileOffset(0)
buffer.length = 0
atEof = false
}
/// Close the underlying file. No reading must be done after calling this method.
func close() -> Void {
fileHandle?.closeFile()
fileHandle = nil
}
}
用法：
if let aStreamReader = StreamReader(path: "/path/to/file") {
defer {
aStreamReader.close()
}
while let line = aStreamReader.nextLine() {
print(line)
}
}
您甚至可以使用读取器进行for-in循环
You can even use the reader with a for-in loop
for line in aStreamReader {
print(line)
}
通过实现 SequenceType 协议（比较 http://robots.thoughtbot.com/swift-sequences ）：
by implementing the SequenceType protocol (compare http://robots.thoughtbot.com/swift-sequences):
extension StreamReader : SequenceType {
func generate() -> AnyGenerator<String> {
return AnyGenerator {
return self.nextLine()
}
}
}
Swift 3 / Xcode 8 beta 6的更新：还将现代化更改为
使用 guard 和新的数据值类型：
Update for Swift 3/Xcode 8 beta 6: Also "modernized" to
use guard and the new Data value type:
class StreamReader {
let encoding : String.Encoding
let chunkSize : Int
var fileHandle : FileHandle!
let delimData : Data
var buffer : Data
var atEof : Bool
init?(path: String, delimiter: String = "\n", encoding: String.Encoding = .utf8,
chunkSize: Int = 4096) {
guard let fileHandle = FileHandle(forReadingAtPath: path),
let delimData = delimiter.data(using: encoding) else {
return nil
}
self.encoding = encoding
self.chunkSize = chunkSize
self.fileHandle = fileHandle
self.delimData = delimData
self.buffer = Data(capacity: chunkSize)
self.atEof = false
}
deinit {
self.close()
}
/// Return next line, or nil on EOF.
func nextLine() -> String? {
precondition(fileHandle != nil, "Attempt to read from closed file")
// Read data chunks from file until a line delimiter is found:
while !atEof {
if let range = buffer.range(of: delimData) {
// Convert complete line (excluding the delimiter) to a string:
let line = String(data: buffer.subdata(in: 0..<range.lowerBound), encoding: encoding)
// Remove line (and the delimiter) from the buffer:
buffer.removeSubrange(0..<range.upperBound)
return line
}
let tmpData = fileHandle.readData(ofLength: chunkSize)
if tmpData.count > 0 {
buffer.append(tmpData)
} else {
// EOF or read error.
atEof = true
if buffer.count > 0 {
// Buffer contains last line in file (not terminated by delimiter).
let line = String(data: buffer as Data, encoding: encoding)
buffer.count = 0
return line
}
}
}
return nil
}
/// Start reading from the beginning of file.
func rewind() -> Void {
fileHandle.seek(toFileOffset: 0)
buffer.count = 0
atEof = false
}
/// Close the underlying file. No reading must be done after calling this method.
func close() -> Void {
fileHandle?.closeFile()
fileHandle = nil
}
}
extension StreamReader : Sequence {
func makeIterator() -> AnyIterator<String> {
return AnyIterator {
return self.nextLine()
}
}
}
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