iphone - 我可以调用 ViewController 类中的什么方法来检查它何时被带到前台？

Question

我可以调用 ViewController 类中的什么方法来检查它何时被带到前台？

例如，我正在查看我的应用程序上的一个页面，然后我决定关闭该应用程序并稍后再返回。当我回到它时，屏幕上出现了与我看到的相同的 View 。但是...一旦我打开应用程序，我就想切换到另一个 View 。

我怎样才能做到这一点？

目前正在尝试这个:

 - (void) applicationDidBecomeActive:(NSNotification*) notification
{
    [self checkActivity];
    // Do your stuff here
}


- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(applicationWillEnterForeground:)
                                                     name:UIApplicationWillEnterForegroundNotification
                                                   object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(applicationDidBecomeActive:)
                                                     name:UIApplicationDidBecomeActiveNotification
                                                   object:nil];
    }
    return self;
}

- (void)checkActivity{
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    NSLog(@"Checking if re-authentication required...");
    if([[defaults objectForKey:@"shouldgotologin"] isEqualToString:@"yes"]){
        NSLog(@"View Should go to login...performing segue");
        [defaults setObject:@"no" forKey:@"shouldgotologin"];
        [defaults synchronize];
        [self performSegueWithIdentifier:@"backtologin" sender:self];
    } else {
        NSLog(@"Should go to login is not true.");
    }
}

Answer 1

注册您的 View Controller 以观察 UIApplicationWillEnterForegroundNotification :

1)内部 View Controller 的init方法:

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(applicationWillEnterForeground:)
                                             name:UIApplicationWillEnterForegroundNotification
                                           object:nil];

2)内部 View Controller 的dealloc方法:

[[NSNotificationCenter defaultCenter] removeObserver:self];

3)另外，让你的 View Controller 实现这个方法:

- (void) applicationWillEnterForeground:(NSNotification*) notification
{
    // This method will be called just before entering the foreground;
    // Do your stuff here
}

如果 UIApplicationWillEnterForegroundNotification的时间不适合您，请查看 UIApplication 的所有可用通知这里:
http://developer.apple.com/library/ios/#DOCUMENTATION/UIKit/Reference/UIApplication_Class/Reference/Reference.html