首先写一个string类扩展 NSString +URL

.h文件里面这么写

//
//  NSString+URL.h
//  iOS_AES
//
//  Created by 琦琦 on 2017/5/8.
//  Copyright © 2017年 cong. All rights reserved.
//

/**
 *  url字符串中具有特殊功能的特殊字符的字符串，或者中文字符,作为参数用GET方式传递时，需要用urlencode处理一下。
 *
 *  例如：在 iOS 程序访问 HTTP 资源时，像拼出来的http://unmi.cc?p1=%+&sd f&p2=中文，其中的中文、特殊符号&％和空格都必须进行转译才能正确访问。
 */

/**
 *  调用示例：
 引入头文件：NSString+URL.h
 
 // URLEncode
 NSString *unencodedString = @"cc?p1=%+&sd f&p";
 NSString *encodedString = [unencodedString URLEncodedString];
 
 // URLDecode
 NSString *undecodedString = @"%25+&sd%20&p2=%E4%B8%AD%E6%96%87";
 NSString *decodedString = [undecodedString URLDecodedString];
 */

#import <Foundation/Foundation.h>

@interface NSString (URL)

/**
 *  URLEncode
 */
- (NSString *)URLEncodedString;

/**
 *  URLDecode
 */
-(NSString *)URLDecodedString;

@end

.m里面这么去实现

//
//  NSString+URL.m
//  iOS_AES
//
//  Created by 琦琦 on 2017/5/8.
//  Copyright © 2017年 cong. All rights reserved.
//

#import "NSString+URL.h"

@implementation NSString (URL)

/**
 *  URLEncode
 */
- (NSString *)URLEncodedString
{
    // CharactersToBeEscaped = @":/?&=;+!@#$()~',*";
    // CharactersToLeaveUnescaped = @"[].";
    
    NSString *unencodedString = self;
    NSString *encodedString = (NSString *)
    CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
                                                              (CFStringRef)unencodedString,
                                                              NULL,
                                                              (CFStringRef)@"!*'();:@&=+$,/?%#[]",
                                                              kCFStringEncodingUTF8));
    
    return encodedString;
}

/**
 *  URLDecode
 */
-(NSString *)URLDecodedString
{
    //NSString *decodedString = [encodedString stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding ];
    
    NSString *encodedString = self;
    NSString *decodedString  = (__bridge_transfer NSString *)CFURLCreateStringByReplacingPercentEscapesUsingEncoding(NULL,
                                                                                                                     (__bridge CFStringRef)encodedString,
                                                                                                                     CFSTR(""),
                                                                                                                     CFStringConvertNSStringEncodingToEncoding(NSUTF8StringEncoding));
    return decodedString;
}

@end

调用已经在.h里面说明了，好了，拿去用吧！