NSString自带的的方法ＵＲＬ ｅｎｃｏｄｉｎｇ的编码问题

NSString *password = @"Top+Secret. ";
NSString *encoded_normal = [password stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSString *encoded_safer = (NSString *)CFURLCreateStringByAddingPercentEscapes(NULL,  (CFStringRef)password,  NULL,  (CFStringRef)@"!*'();:@&=+$,/?%#[]",  kCFStringEncodingUTF8);
 
// output with %@ otherwise the % escapes cause strange output
NSLog(@"%@", password);
NSLog(@"%@", encoded_normal);
NSLog(@"%@", encoded_safer);
通过输出情况看，用
stringByAddingPercentEscapesUsingEncoding：方法编码时，+号没有编码，存在不ｅｎｃｏｄｅ的情况
推荐使用
CFURLCreateStringByAddingPercentEscapes（）
下面是一个给ＮＳＳｔｒｉｎｇ添加的类别，来实现ｅｎｃｏｄｅ
#import 
 
@interface NSString (Helpers)
 
// helper functions
- (NSString *) stringByUrlEncoding;
 
@end

#import "NSString+Helpers.h"
 
@implementation NSString (Helpers)
 
#pragma mark Helpers
- (NSString *) stringByUrlEncoding
{
	return (NSString *)CFURLCreateStringByAddingPercentEscapes(NULL,  (CFStringRef)self,  NULL,  (CFStringRef)@"!*'();:@&=+$,/?%#[]",  kCFStringEncodingUTF8);
}