ios - 如何捕获后退按钮事件

Question

我有一个启动 UIViewController 的 UITableViewController，我想在子 Controller 中按下后退按钮时捕获，这是从“UIViewController”派生的类。我可以更改后退按钮标题，但在设置 backBarButtonItem 时设置目标和操作值似乎被忽略了。有什么方法可以接收某种类型的“后退”按钮被点击的通知？

- (void)showDetailView 
{
    // How I'm creating & showing the detail controller
    MyViewController *controller = [[MyViewController alloc] initWithNibName:@"MyDetailView" bundle:nil];   

    UIBarButtonItem *backButton = [[UIBarButtonItem alloc] initWithTitle:@"Pages"
                            style:UIBarButtonItemStyleBordered 
                            target:self                                     
                            action:@selector(handleBack:)];

    self.navigationItem.backBarButtonItem = backButton;
    [backButton release];

    [self.navigationController pushViewController:controller animated:animated];
    [controller release];

}   

- (void)handleBack:(id)sender
{
    // not reaching here
    NSLog(@"handleBack event reached");
}

Answer 1

您可以实现 UIViewController 的 viewWillDisappear 方法。当您的 Controller 即将离开时会调用此方法(因为另一个 Controller 被推到导航 Controller 堆栈上，或者因为按下了“后退”按钮)。

要确定 View 是否因为按下后退按钮而消失，您可以使用在将新 Controller 推到导航 Controller 的任何地方设置的自定义标志，如下所示

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    if (viewPushed) {
        viewPushed = NO;   // Flag indicates that view disappeared because we pushed another controller onto the navigation controller, we acknowledge it here
    } else {
        // Here, you know that back button was pressed
    }   
}

无论你在哪里推送一个新的 View Controller ，你都必须记住也要设置那个标志......

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    ...
    viewPushed = YES;
    [self.navigationController pushViewController:myNewController animated:YES];
    ...
}