hidesBottombarWhenPushed的副作用

在UITabbarController包含的UINavigationController应用中，如果UINavigationController某一页（某个level）需要隐藏Tabbar，之前的做法是在push那一页之前，将那一页的ViewController中的hidesBottombarWhenPushed参数设为YES，这样当那一页push进UINavigationController中时，底部的Tabbar就会隐藏掉。

但是这种方法有一个潜在的而又巨大的问题，假设现在我有3个ViewController A,B,C，其中为Navigation的RootViewController，A中push B，B中push C。这时，如果我想要在B中隐藏Tabbar，而在C中显示Tabbar，根据最朴素的想法就是：

//SecondLevel即为B，此代码在A中进行
SecondLevelViewController *_2vc = [[SecondLevelViewController alloc]initWithNibName:@"SecondLevelViewController" bundle:nil];
_2vc.hidesBottomBarWhenPushed = YES;
[self.navigationController pushViewController:_2vc animated:YES]; 

//ThirdLevel即为C，此代码在B中进行
ThirdLevelViewController *_3vc = [[ThirdLevelViewController alloc]initWithNibName:@"ThirdLevelViewController" bundle:nil];
_3vc.hidesBottomBarWhenPushed = NO;
[self.navigationController pushViewController:_3vc animated:YES];

然而很可惜，虽然A中push B能让Tabbar隐藏，但是B中push C，就没办法让Tabbar显示出来了。这是一个比较郁闷的问题，我只能猜想其中的原理是，当设置某一层hidesBottomBarWhenPushed = YES之后，UITabbarController就像不存在一样，就连调用self.tabbarController或者self.navigationController.tabbarController也应该是nil。

所以解决办法只能是手动隐藏Tabbar。

在B中，加入以下代码：

- (void) hideTabBar:(UITabBarController *) tabbarcontroller {
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationDuration:0.5];
    for(UIView *view in tabbarcontroller.view.subviews)
    {
        if([view isKindOfClass:[UITabBar class]])
        {
            [view setFrame:CGRectMake(view.frame.origin.x, 480, view.frame.size.width, view.frame.size.height)];
        } 
        else
        {
            [view setFrame:CGRectMake(view.frame.origin.x, view.frame.origin.y, view.frame.size.width, 480)];
        }
    }
    [UIView commitAnimations];
}
 
- (void) showTabBar:(UITabBarController *) tabbarcontroller {
 
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationDuration:0.5];
    for(UIView *view in tabbarcontroller.view.subviews)
    {
        NSLog(@"%@", view);
 
        if([view isKindOfClass:[UITabBar class]])
        {
            [view setFrame:CGRectMake(view.frame.origin.x, 431, view.frame.size.width, view.frame.size.height)];
        } 
        else
        {
            [view setFrame:CGRectMake(view.frame.origin.x, view.frame.origin.y, view.frame.size.width, 431)];
        }
    }
 
    [UIView commitAnimations]; 
}
 
-(void)viewWillAppear:(BOOL)animated
{
   [super viewWillAppear:animated];
   [self hideTabbar:self.tabbarController];
}
 
-(void)viewWillDisAppear:(BOOL)animated
{
   [super viewWillDisAppear:animated];
   [self showTabbar:self.tabbarController];
}