#define iOS8Later ([UIDevice currentDevice].systemVersion.doubleValue >= 8.0)

@interface RootViewController ()<UIAlertViewDelegate> 
 
@end 

UIAlertView * alert = [[UIAlertView alloc] initWithTitle:@"登陆失败" message:@"请重新输入用户名和密码" delegate:self cancelButtonTitle:@"取消" otherButtonTitles:@"确定", nil]; 
      [alert show]; 

#pragma mark - UIAlertView Delegate Methods - 
- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex 
{ 
  if(buttonIndex == 0) 
  { 
    NSLog(@"点击取消按钮后，想要的操作,可以加此处"); 
  } 
  else if(buttonIndex == 1) 
  { 
    NSLog(@"点击确定按钮后，想要的操作，可以加此处"); 
  } 
} 

      UIAlertController *_alertVC = [UIAlertController alertControllerWithTitle:@"登陆失败" message:@"请重新输入用户名和密码" preferredStyle:UIAlertControllerStyleAlert]; 
       
      //警告类型，红色字体 UIAlertActionStyleDestructive 
//      UIAlertAction *_doAction = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDestructive handler:nil]; 
//      [_alertVC addAction:_doAction]; 
       
      UIAlertAction *_doAction = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) 
      { 
        NSLog(@"点击确定按钮后，想要的操作，可以加此处"); 
      }]; 
      [_alertVC addAction:_doAction]; 
 
//      UIAlertAction *_cancleAction = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:nil]; 
//      [_alertVC addAction:_cancleAction]; 
       
      UIAlertAction *_cancleAction = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) 
      { 
        NSLog(@"点击取消按钮后，想要的操作"); 
      }]; 
      [_alertVC addAction:_cancleAction]; 
       
      [self presentViewController:_alertVC animated:YES completion:nil]; 

//警告类型，红色字体 UIAlertActionStyleDestructive，如下图所示的效果

      UIAlertAction *_doAction = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDestructive handler:nil];

      [_alertVC addAction:_doAction];