警告框

- (void)showAlert:(NSString *)title message:(NSString *)message {
    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];
    UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDestructive handler:nil];
    [alertController addAction:okAction];
    [self presentViewController:alertController animated:YES completion:nil];
}