注意：cancelButton的index == 0

- (void)PWtypeClicked:(UIButton *)btn {
    NSLog(@"點擊選擇類型密碼按鈕");
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"選擇密碼類型" message:nil delegate:self cancelButtonTitle:@"一級密碼" otherButtonTitles:@"二級密碼", nil];
    [alert show];
}

pragma mark -- alertDelegate

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    UITextField *tmpField = (UITextField *)[self.view viewWithTag:100];
    if (buttonIndex == 0) {
        tmpField.text = @"一級密碼";
    } else if(buttonIndex == 1){
        tmpField.text = @"二級密碼";
    }
}