gistfile1.m

            NSArray * strings = [text componentsSeparatedByString:@"@"];
            if([strings count] == 2) {
                NSString * string = [strings objectAtIndex:0];
                NSCharacterSet * set = [NSCharacterSet characterSetWithCharactersInString:@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890.-"];
                set = [set invertedSet];
                if ([string length]) { //@之前不是空字串
                    range = [string rangeOfCharacterFromSet:set];
                    if (NSNotFound == range.location) { //只包含合法字符
                        string = [strings objectAtIndex:1];
                        if ([string length]) { //@之后不是空字串
                            range = [string rangeOfCharacterFromSet:set];
                            if (NSNotFound == range.location) {//不包含非法字符
                                strings = [string componentsSeparatedByString:@"."];
                                if ([strings count] >= 2 && [[strings objectAtIndex:1] length]) { //至少有一级域名
                                    [self.navigationItem setRightBarButtonItem:self.registerBarButtonItem animated:YES];
                                    return ;
                                }
                            }
                        }
                    }
                }
            }