• (NSString )stringByAddingPercentEscapesUsingEncodingExt:(NSStringEncoding)enc stringWith:(NSString )str
  {
  if([str respondsToSelector:@selector(stringByAddingPercentEncodingWithAllowedCharacters:)] == YES)
  {
  NSCharacterSet set = [[NSCharacterSet characterSetWithCharactersInString:@"!'();:@&=+$,/?%#[]"] invertedSet];
  return [str stringByAddingPercentEncodingWithAllowedCharacters:set];
  }
  else
  {

pragma clang diagnostic push

pragma clang diagnostic ignored "-Wdeprecated-declarations"

// NSString * newString = (__bridge_transfer NSString *)
NSString * newString = ( NSString )
CFURLCreateStringByAddingPercentEscapes(NULL,
(__bridge CFStringRef)str,
NULL,
(CFStringRef)@"!'();:@&=+$,/?%#[]",
CFStringConvertNSStringEncodingToEncoding(enc));

pragma clang diagnostic pop

    return newString;
}

}

调用
content = [self stringByAddingPercentEscapesUsingEncodingExt:NSUTF8StringEncoding stringWith:content];