向 UINavigationBar 后退按钮添加方法？

如何向 UINavigationbar 后退按钮添加方法，以便每当我单击该后退按钮时，我需要检查一些值并显示 UIAlertView？有什么选择吗？

我尝试过这个方法，但它对我有用

  - (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated 
    {
    //show alert 
    }

还有这个方法，但都不起作用

-(void) viewWillDisappear:(BOOL)animated {
    if ([self.navigationController.viewControllers indexOfObject:self]==NSNotFound) {
        // back button was pressed.  We know this is true because self is no longer
        // in the navigation stack.
         NSLog(@"hi");
    }

是的你可以 在 viewDidLoad 中

UIBarButtonItem * backBtn = [[UIBarButtonItem alloc]initWithTitle:@"Back" style:UIBarButtonItemStyleBordered target:self action:@selector(goBackToAllPets:)];

    self.navigationItem.leftBarButtonItem = backBtn;

编写以下函数来检查条件

-(void)goBackToAllPets:(id)sender
{
    if(/*check condition*/)
    {
        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:nil message:@"message" delegate:self cancelButtonTitle:@"No" otherButtonTitles:@"Yes", nil];
        alert.tag = 0;
        [alert show];


    }
    else
    {
        [self.navigationController popViewControllerAnimated:YES];
    }


}