Swift 3 +

let plainString = "foo"

编码中

let plainData = plainString.data(using: .utf8)
let base64String = plainData?.base64EncodedString()
print(base64String!) // Zm9v

解码

if let decodedData = Data(base64Encoded: base64String!),
let decodedString = String(data: decodedData, encoding: .utf8) {
print(decodedString) // foo
}

迅速 < 3

let plainString = "foo"

编码中

let plainData = plainString.dataUsingEncoding(NSUTF8StringEncoding)
let base64String = plainData?.base64EncodedStringWithOptions(NSDataBase64EncodingOptions(rawValue: 0))
print(base64String!) // Zm9v

解码

let decodedData = NSData(base64EncodedString: base64String!, options: NSDataBase64DecodingOptions(rawValue: 0))
let decodedString = NSString(data: decodedData, encoding: NSUTF8StringEncoding)
print(decodedString) // foo

目标 C

NSString *plainString = @"foo";

编码中

NSData *plainData = [plainString dataUsingEncoding:NSUTF8StringEncoding];
NSString *base64String = [plainData base64EncodedStringWithOptions:0];
NSLog(@"%@", base64String); // Zm9v

解码

NSData *decodedData = [[NSData alloc] initWithBase64EncodedString:base64String options:0];
NSString *decodedString = [[NSString alloc] initWithData:decodedData encoding:NSUTF8StringEncoding];
NSLog(@"%@", decodedString); // foo

如果你想编写后备代码，iOS 从一开始就提供了 base64的解码，但是 NSURL提出了警告:

NSURL *URL = [NSURL URLWithString:
[NSString stringWithFormat:@"data:application/octet-stream;base64,%@",
base64String]];


return [NSData dataWithContentsOfURL:URL];