ios - 将方法添加到UINavigationBar后退按钮？

Question

如何将方法添加到UINavigationbar的后退按钮，所以每当我单击该后退按钮时，我都需要检查一些值并显示UIAlertView？有什么选择吗？

我尝试过这种方法，但对我有用

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

而且这种方法，但都没有

-(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");
    }

Answer 1

是的你可以
在viedDidLoad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];
    }


}