（该代码现在适用于Swift 2.2 / Xcode 7.3。如果有人需要，可以在编辑历史记录中找到旧版本。最后提供了Swift 3的更新版本。）
以下Swift代码从如何逐行从NSFileHandle中读取数据的各种答案中获得了很大的启发
。。它从文件中分块读取，并将完整的行转换为字符串。
\n可以使用可选参数设置默认行定界符（），字符串编码（UTF-8）和块大小（4096）。
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()
}
func nextLine() -> String? {
precondition(fileHandle != nil, "Attempt to read from closed file")
if atEof {
return nil
}
var range = buffer.rangeOfData(delimData, options: [], range: NSMakeRange(0, buffer.length))
while range.location == NSNotFound {
let tmpData = fileHandle.readDataOfLength(chunkSize)
if tmpData.length == 0 {
atEof = true
if buffer.length > 0 {
let line = NSString(data: buffer, encoding: encoding)
buffer.length = 0
return line as String?
}
return nil
}
buffer.appendData(tmpData)
range = buffer.rangeOfData(delimData, options: [], range: NSMakeRange(0, buffer.length))
}
let line = NSString(data: buffer.subdataWithRange(NSMakeRange(0, range.location)),
encoding: encoding)
buffer.replaceBytesInRange(NSMakeRange(0, range.location + range.length), withBytes: nil, length: 0)
return line as String?
}
func rewind() -> Void {
fileHandle.seekToFileOffset(0)
buffer.length = 0
atEof = false
}
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)
}
}
您甚至可以将阅读器与for-in循环一起使用
for line in aStreamReader {
print(line)
}
通过实施SequenceType协议（比较http://robots.thoughtbot.com/swift-sequences）：
extension StreamReader : SequenceType {
func generate() -> AnyGenerator<String> {
return AnyGenerator {
return self.nextLine()
}
}
}
Swift 3 / Xcode 8 beta 6更新：还要“现代化”使用guard和新 Data值类型：
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()
}
func nextLine() -> String? {
precondition(fileHandle != nil, "Attempt to read from closed file")
while !atEof {
if let range = buffer.range(of: delimData) {
let line = String(data: buffer.subdata(in: 0..<range.lowerBound), encoding: encoding)
buffer.removeSubrange(0..<range.upperBound)
return line
}
let tmpData = fileHandle.readData(ofLength: chunkSize)
if tmpData.count > 0 {
buffer.append(tmpData)
} else {
atEof = true
if buffer.count > 0 {
let line = String(data: buffer as Data, encoding: encoding)
buffer.count = 0
return line
}
}
}
return nil
}
func rewind() -> Void {
fileHandle.seek(toFileOffset: 0)
buffer.count = 0
atEof = false
}
func close() -> Void {
fileHandle?.closeFile()
fileHandle = nil
}
}
extension StreamReader : Sequence {
func makeIterator() -> AnyIterator<String> {
return AnyIterator {
return self.nextLine()
}
}
}