objective - c:

NSString *str = @"test string";
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:str];
NSString *thatStr = [NSKeyedUnarchiver unarchiveObjectWithData:data];

迅速:

let str = "test string"
let data = NSKeyedArchiver.archivedData(withRootObject: str)
let thatStr = NSKeyedUnarchiver.unarchiveObject(with: data) as! String

objective - c:

NSString to NSData：

NSString* str= @"string";
NSData* data=[str dataUsingEncoding:NSUTF8StringEncoding];

NSData to NSString：

NSString* newStr = [[NSString alloc] initWithData:theData encoding:NSUTF8StringEncoding];

迅速:

字符串到数据:

var testString = "string"
var somedata = testString.data(using: String.Encoding.utf8)

数据到字符串:

var backToString = String(data: somedata!, encoding: String.Encoding.utf8) as String!

NSString *str = @"Banana";
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:true];

NSString *str = @"hello";
NSData *data = [NSData dataWithBytes:str.UTF8String length:str.length];

objective - c:

NSString *str = @"test string";
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:str];
NSString *thatStr = [NSKeyedUnarchiver unarchiveObjectWithData:data];

迅速:

let str = "test string"
let data = NSKeyedArchiver.archivedData(withRootObject: str)
let thatStr = NSKeyedUnarchiver.unarchiveObject(with: data) as! String

NSString* str = @"teststring";
NSData* data = [str dataUsingEncoding:NSUTF8StringEncoding];