1.iOS8之后只需要设置一个最新的属性

 SecondViewController *secondVC = [[SecondViewController alloc] init];
 secondVC.modalPresentationStyle = UIModalPresentationOverCurrentContext;
 //self.tabBarController.tabBar.hidden = YES;  当presentingVC有根视图控制器tabBarController，隐藏tabBar
 secondVC.view.backgroundColor = [UIColor colorWithRed:0 green:0 blue:0 alpha:.14]; 
 [self presentViewController:secondVC animated:YES completion:^{
  }];

如果当presentingVC有根视图控制器tabBarController，上面的设置会使tabBar未被覆盖，意思就好像是你有一直看到presentingVC直接导致不会走viewWiillAppear，不能在原视图即将出现时把隐藏tabBar的属性改回来。

2.在SecondViewController设置

- (void)viewDidLoad {
    [super viewDidLoad];
//模糊视图
    UIBlurEffect *beffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleExtraLight];
    UIVisualEffectView *visualEffect = [[UIVisualEffectView alloc]initWithEffect:beffect];
    visualEffect.frame = CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height);
    visualEffect.alpha = 0.7;
    [self.view addSubview:visualEffect];
}
- (void)viewWillDisappear:(BOOL)animated
{
    self.presentingViewController.tabBarController.tabBar.hidden = NO;
}