iphone - 将 leftBarButtonItem 添加到导航栏时出现问题

Question

我有一个 UINavigationController，其中我的 AHViewController 作为 Root View Controller 。

然后我尝试从 AHViewController 的 viewDidLoad 向其添加一个左栏按钮项:

UIButton * backButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [backButton addTarget:self action:@selector(backButtonPressed) forControlEvents:UIControlEventTouchUpInside];
    [backButton setImage:[UIImage imageNamed:@"grid.png"] forState:UIControlStateNormal];
    UIBarButtonItem *backButtonBarItem = [[UIBarButtonItem alloc] initWithCustomView:backButton];
    //[self.navigationItem setLeftBarButtonItem:backButtonBarItem];
    [self.navigationController.navigationItem setLeftBarButtonItem:backButtonBarItem];
    [backButtonBarItem release];

但是，我什么也没看到。这是为什么？

Answer 1

而不是:

[self.navigationController.navigationItem setLeftBarButtonItem:backButtonBarItem];

这样做:

[self.navigationItem setLeftBarButtonItem:backButtonBarItem];

UINavigationController 使用顶部 View Controller 的 navigationItem，而不是其(UINavigationController 的)导航项属性。