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

//URLEncode

  +(NSString*)encodeString:(NSString*)unencodedString{

    if([[[UIDevicecurrentDevice]systemVersion]floatValue] >=9.0) {

            return[unencodedString stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLPathAllowedCharacterSet]];

}

NSString*encodedString = (NSString*)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,(CFStringRef)unencodedString,NULL,(CFStringRef)@"!*'();:@&=+$,/?%#[]",kCFStringEncodingUTF8));

returnencodedString;
}

//URLDEcode

-(NSString *)decodeString:(NSString*)encodedString

{

//NSString *decodedString = [encodedString stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding ];

NSString *decodedString  = (__bridge_transfer NSString *)CFURLCreateStringByReplacingPercentEscapesUsingEncoding(NULL,

(__bridge CFStringRef)encodedString,

CFSTR(""),

CFStringConvertNSStringEncodingToEncoding(NSUTF8StringEncoding));

return decodedString;

有用户反馈，说iOS9之后，CFURLCreateStringByAddingPercentEscapes这个方法废弃，所以根据官方的描述 替换使用stringByAddingPercentEncodingWithAllowedCharacters 这个方法。

stringByAddingPercentEncodingWithAllowedCharacters 需要传递参数NSCharacterSet 。