如何捕获后退按钮事件 [英] How to trap the back button event

问题描述

我有一个UITableViewController，它启动一个UIViewController，我想在子控制器中按下后退按钮时陷阱，这是从'UIViewController'派生的类。我可以更改后退按钮标题，但设置目标&设置backBarButtonItem时的动作值似乎被忽略了。有什么方法可以获得点击后退按钮的某种通知？

I have a UITableViewController that launches a UIViewController and I would like to trap whenever the back button is pressed in the child controller, which is the class that derives from 'UIViewController'. I can change the Back Button title but setting the target & action values when setting the backBarButtonItem seems to get ignored. What's a way to receiving some kind of notification that the Back button was tapped?

- (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");
}

推荐答案

你可以实现 viewWillDisappear UIViewController的方法。当你的控制器即将消失时，这会被调用（因为另一个被推到导航控制器堆栈上，或者因为按下了'后退'按钮）。

You can implement the viewWillDisappear method of UIViewController. This gets called when your controller is about to go away (either because another one was pushed onto the navigation controller stack, or because the 'back' button was pressed).

要确定视图是否因按下后退按钮而消失，您可以使用在将新控制器推入导航控制器的任何位置设置的自定义标志，如下所示

To determine whether the view is disappearing because of the back button being pressed, you can use a custom flag that you set wherever you push a new controller onto the navigation controller, like shown below

- (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
    }   
}

无论你在哪里推新的视图控制器，你都必须记得同时设置flag ...

And wherever you push a new view controller, you would have to remember to also set that flag...

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

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