- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string;

{

    NSString * toBeString = [textField.text stringByReplacingCharactersInRange:range withString:string];

    UITextField *loginPass = _textArr[1];

    if (loginPass == textField) {

        if ([toBeString length] > 12) {

            textField.text = [toBeString substringToIndex:12];

            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"长度不能超过12" delegate:nil cancelButtonTitle:@"ok" otherButtonTitles:nil, nil];

            [alert show];

            return NO;

        }

    }

    return YES;

}