更新Swift 5.x

let str = "teststring"
let data = str.data(using: .utf8)

objective - c

NSString *str = @"Hello World";
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:NO];

斯威夫特

let str = "Hello World"
let data = string.data(using: String.Encoding.utf8, allowLossyConversion: false)

更新Swift 5.x

let str = "teststring"
let data = str.data(using: .utf8)

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

以防Swift开发者来这里，

将NSString / String转换为NSData

var _nsdata = _nsstring.dataUsingEncoding(NSUTF8StringEncoding)

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!