为什么 iOS 模拟器中应用程序退出时不调用 viewWillDisappear 或 viewDidDisappear？

Question

我试图在应用程序退出时调用removeObserver() 。但是当我使用NSLog()检查时，我发现在 iOS 模拟器中应用程序退出后，viewWillDisappear()和viewDidDisappear()都没有被调用。在类似的问题中，我使用的是单个视图模板，而不是导航控制器。

这是源代码：

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"viewDidLoad() called");
    // Do any additional setup after loading the view, typically from a nib.

    NSString *filePath = [self dataFilePath];
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
        NSArray *array = [[NSArray alloc] initWithContentsOfFile:filePath];
        for (int i = 0; i < 4; i++) {
            UITextField *theField = self.lineFields[i];
            theField.text = array[i];
        }
    }

    UIApplication *app = [UIApplication sharedApplication];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(applicationWillResignActive:)
                                                 name:UIApplicationWillResignActiveNotification
                                               object:app];

}

- (void)viewWillDisappear:(BOOL)animated {
    NSLog(@"viewWillDisappear() called");
    [super viewWillDisappear:animated];
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (NSString *)dataFilePath {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentDirectory = paths[0];
    return [documentDirectory stringByAppendingPathComponent:@"data.plist"];
}

- (void)applicationWillResignActive:(NSNotification *)notification {
    NSString *filePath = [self dataFilePath];
    NSArray *array = [self.lineFields valueForKey:@"text"];
    [array writeToFile:filePath atomically:YES];
}

@end

Answer 1

我建议您添加应用程序更改的侦听器：

- (void)registerNotifications {
    // Add observers to application state changes
    [[NSNotificationCenter defaultCenter]addObserver:self
                                            selector:@selector(applicationDidEnterBackground:)
                                                name:UIApplicationDidEnterBackgroundNotification
                                              object:nil];

    [[NSNotificationCenter defaultCenter]addObserver:self
                                            selector:@selector(applicationDidBecomeActive:)
                                                name:UIApplicationDidBecomeActiveNotification
                                              object:nil];
}