以往我們隱藏導(dǎo)航欄都是這樣做：

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
   [self.navigationController setNavigationBarHidden:YES animated:YES];
}
-(void)viewWillDisappear:(BOOL)animated{
    [super viewWillDisappear:animated];
    [self.navigationController setNavigationBarHidden:NO animated:YES];
}

但是往往這樣 會(huì)遇到一些奇怪的 bug ，想來想去 我想到這樣做可能要更好一點(diǎn):

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    [self.navigationController.view sendSubviewToBack:self.navigationController.navigationBar];
}

-(void)viewWillDisappear:(BOOL)animated{
    [super viewWillDisappear:animated];
    [self.navigationController.view bringSubviewToFront:self.navigationController.navigationBar];
}