单独使用NavigationBar

可能80%的情况下，NavigationBar都是和UINavigationController一起使用的。这样设置NavigationItem比较简单，直接通过ViewController的self.navigationItem属性就可以设置：

UIButton *switchShop = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 20, 20)];
[switchShop setBackgroundImage:[UIImage imageNamed:@"switch_shop"] forState:UIControlStateNormal];
[switchShop addTarget:self action:@selector(switchButtonTapped) forControlEvents:UIControlEventTouchUpInside];
self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:switchShop];

但是在特殊情况下，NavigationBar也可以脱离NavigationController单独使用。这样就需要手工创建NavigationBar，NavigationItem，并手工加到view上：

-(void) loadView
{
    RegisterView *view = [[RegisterView alloc] initWithController:self];
    self.view = view;
    
    UINavigationBar *navigationBar = [[UINavigationBar alloc] initWithFrame:CGRectMake(0, 0, 320, 66)];

    UINavigationItem *navigationItem = [[UINavigationItem alloc] initWithTitle:nil];
    
    if([self.type isEqualToString:@"register"]){
        navigationItem.title = @"注册";
    }else{
        navigationItem.title = @"重置密码";
    }
    
    UIBarButtonItem *backButton = [[UIBarButtonItem alloc] initWithTitle:@"关闭" style:UIBarButtonItemStyleBordered target:self action:@selector(back)];
    navigationItem.leftBarButtonItem = backButton;
    
    [navigationBar pushNavigationItem:navigationItem animated:NO];
    
    [self.view addSubview:navigationBar];
}