URL编码：

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

  return encodedString;
  }

URL解码：

• (NSString *)URLDecodedString
  {
  NSString *result = [(NSString *)self stringByReplacingOccurrencesOfString:@"+" withString:@" "];
  return [result stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
  }

建议这两个方法放在NSString的分类中，并且声明为实例方法，这样可以直接用NSString的对象去调用。