如何将一个 NSString 值转换为 NSData？

How do I convert an NSString value to NSData?

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

Do:

NSData *data = [yourString dataUsingEncoding:NSUTF8StringEncoding];

then feel free to proceed with NSJSONSerialization:JSONObjectWithData.

Correction to the answer regarding the NULL terminator

Following the comments, official documentation, and verifications, this answer was updated regarding the removal of an alleged NULL terminator:

1. As documented by dataUsingEncoding::

   Return Value

   The result of invoking dataUsingEncoding:allowLossyConversion: with NO as the second argument

2. As documented by getCString:maxLength:encoding: and cStringUsingEncoding::

   note that the data returned by dataUsingEncoding:allowLossyConversion: is not a strict C-string since it does not have a NULL terminator

First off, you should use dataUsingEncoding: instead of going through UTF8String. You only use UTF8String when you need a C string in that encoding.

Then, for UTF-16, just pass NSUnicodeStringEncoding instead of NSUTF8StringEncoding in your dataUsingEncoding: message.

In case of Swift Developer coming here,

to convert from NSString / String to NSData

var _nsdata = _nsstring.dataUsingEncoding(NSUTF8StringEncoding)

NSString *str = @"helowrld";
// This converts the string to an NSData object
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];

you can take reference from this link

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];

Swift:

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

For Swift 3, you will mostly be converting from String to Data.

let myString = "test"
let myData = myString.data(using: .utf8)
print(myData) // Optional(Data)

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

Objective-C

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

Swift

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