当没有后退按钮时，向UINavigationController添加一个左栏按钮项目

Question

我想添加一个默认的左栏按钮项目到我的导航栏。只有当UINavigationController没有提供后退按钮时才会显示它。

什么是最好的方法？

Answer 1

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated { 
    if(navigationController.viewControllers.count != 1) { // not the root controller - show back button instead 
     return; 
    } 
    UIBarButtonItem *menuItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemOrganize 
                       target:self 
                       action:@selector(menuItemSelected:)]; 
    [viewController.navigationItem setLeftBarButtonItem:menuItem]; 
} 

Answer 2

斯威夫特代码添加leftBarButtonItem ......

let leftMenuItem = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.Done, target: self, action: "leftMenuItemSelected:"); 
    self.navigationItem.setLeftBarButtonItem(leftMenuItem, animated: false); 

Answer 3

斯威夫特3版本：

let done = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(YourController.done)) 
navigationItem.setLeftBarButtonItem(done, animated: false)