base64

NSData編碼成NSString

NSData *encodeData = [decodeString dataUsingEncoding:NSUTF8StringEncoding];
NSString *base64String = [encodeData base64EncodedStringWithOptions:0];

NSString解碼成NSData

NSData *decodedData = [[NSData alloc] initWithBase64EncodedString:base64String options:0];
NSString *decodedString = [[NSString alloc] initWithData:decodedData encoding:NSUTF8StringEncoding];