NSString 的一个类别，用于验证电子邮件或密码字符串

有效密码

/*
 ensures the string contains letters and no decimal characters
 also checks for:
    minLength = 6
    maxLength = 20
    hasUppercase = YES
    hasLowercase = YES
    hadNumbers = NO
*/

- (BOOL)isValidPassword;

/* 
 customize your own password criteria!
*/
- (BOOL)isValidPasswordWithMinLength:(int)minLength
                           maxLength:(int)maxLength
                           uppercase:(BOOL)hasUppercase
                           lowercase:(BOOL)hasLowercase
                             numbers:(BOOL)hasNumbers
                          alertsShown:(BOOL)alertsShown;

设置 alertsShown 为 yes 将显示失败标准的警告消息

有效电子邮件

检查 [字符串]，[@]，和 [.com]

- (BOOL)isValidEmail;