check VerifyCode

gistfile1.txt

-(NSString *)checkVerifyCode:(NSString *)code
{    
    code = [code stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
    if([code isEqualToString:@""])
    {
        return @"验证码不能为空";
    }  
    
    NSString *verifyCodeRegex = [NSString stringWithFormat:@"([a-z,A-Z,0-9]{6})"];    
    NSPredicate *verifyCodeTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", verifyCodeRegex];
    if ([verifyCodeTest evaluateWithObject:code]==NO) {
        return @"请输入6位，数字，字母验证码";
    }
  
    return nil;
}