iOS 自定义tabbar并修改其高度，push后tabba

在tabBar的视图控制器的生命周期，控制tabbar的隐藏与显示

• (void)viewWillDisappear:(BOOL)animated {
  [super viewWillDisappear:animated];

  self.tabBarController.tabBar.hidden = YES;
  }

-(void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];

self.tabBarController.tabBar.hidden = NO;

}