使用原生的Base64
Base64是使用ASCII码显示二进制数据的一种流行方法。直到现在，开发者还不得不使用开源的工具来编码解码Base64的内容。
现在iOS7引入了以下四种新的NSData方法来操作Base64编码的数据：
- // From NSData.h
- /* Create an NSData from a Base-64 encoded NSString using the given options. By default, returns nil when the input is not recognized
- as valid Base-64.
- */
- - (id)initWithBase64EncodedString:(NSString *)base64String options:(NSDataBase64DecodingOptions)options;
- /* Create a Base-64 encoded NSString from the receiver's contents using the given options.
- */
- - (NSString *)base64EncodedStringWithOptions:(NSDataBase64EncodingOptions)options;
- /* Create an NSData from a Base-64, UTF-8 encoded NSData. By default, returns nil when the input is not recognized as valid Base-64.
- */
- - (id)initWithBase64EncodedData:(NSData *)base64Data options:(NSDataBase64DecodingOptions)options;
- /* Create a Base-64, UTF-8 encoded NSData from the receiver's contents using the given options.
- */
- - (NSData *)base64EncodedDataWithOptions:(NSDataBase64EncodingOptions)options;
这些方法可以帮助你轻易的将NSData对象转化为Base64，或者将Base64转化为NSData object。见以下的例子：
- NSData* sampleData = [@"Some sample data" dataUsingEncoding:NSUTF8StringEncoding];
- NSString * base64String = [sampleData base64EncodedStringWithOptions:0];
- NSLog(@"Base64-encoded string is %@", base64String); // prints "U29tZSBzYW1wbGUgZGF0YQ=="
- NSData* dataFromString = [[NSData alloc] initWithBase64EncodedString:base64String options:0];
- NSLog(@"String is %@",[NSString stringWithUTF8String:[dataFromString bytes]]); // prints "String is Some sample data"
如果你需要支持iOS6或者更早以前的系统，你可以使用以下两个方法：
- /* These methods first appeared in NSData.h on OS X 10.9 and iOS 7.0. They are deprecated in the same releases in favor of the methods in the <code>NSDataBase64Encoding</code> category. However, these methods have existed for several releases, so
- they may be used for applications targeting releases prior to OS X 10.9 and iOS 7.0.
- */
- - (id)initWithBase64Encoding:(NSString *)base64String;
- - (NSString *)base64Encoding;
来自：http://www.cocoachina.com/applenews/devnews/2014/0117/7715.html