빠른

짧은 답변

NotificationCenter대신 관찰자를 사용하십시오 viewWillAppear.

override func viewDidLoad() {
    super.viewDidLoad()

    // set observer for UIApplication.willEnterForegroundNotification
    NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)

}

// my selector that was defined above
@objc func willEnterForeground() {
    // do stuff
}

긴 대답

앱이 백그라운드에서 언제 돌아 오는지 알아 보려면 NotificationCenter대신 관찰자를 사용하십시오 viewWillAppear. 다음은 언제 어떤 이벤트가 발생하는지 보여주는 샘플 프로젝트입니다. (이것은 이 Objective-C 답변 의 적응입니다 .)

import UIKit
class ViewController: UIViewController {

    // MARK: - Overrides

    override func viewDidLoad() {
        super.viewDidLoad()
        print("view did load")

        // add notification observers
        NotificationCenter.default.addObserver(self, selector: #selector(didBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)

    }

    override func viewWillAppear(_ animated: Bool) {
        print("view will appear")
    }

    override func viewDidAppear(_ animated: Bool) {
        print("view did appear")
    }

    // MARK: - Notification oberserver methods

    @objc func didBecomeActive() {
        print("did become active")
    }

    @objc func willEnterForeground() {
        print("will enter foreground")
    }

}

앱을 처음 시작할 때 출력 순서는 다음과 같습니다.

view did load
view will appear
did become active
view did appear

홈 버튼을 누른 다음 앱을 다시 포 그라운드로 가져온 후 출력 순서는 다음과 같습니다.

will enter foreground
did become active 

원래 사용하려고한다면 그래서 viewWillAppear다음 UIApplication.willEnterForegroundNotification당신이 원하는 아마.

노트

iOS 9 이상에서는 관찰자를 제거 할 필요가 없습니다. 설명서 에는 다음 이 명시되어 있습니다.

앱이 iOS 9.0 이상 또는 macOS 10.11 이상을 대상으로하는 경우 해당 dealloc방법으로 옵저버를 등록 해제 할 필요가 없습니다 .

답변

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"view did load");

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

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

- (void)applicationIsActive:(NSNotification *)notification {
    NSLog(@"Application Did Become Active");
}

- (void)applicationEnteredForeground:(NSNotification *)notification {
    NSLog(@"Application Entered Foreground");
}

override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground),
                                           name: Notification.Name.UIApplicationWillEnterForeground,
                                           object: nil)
}

@objc func willEnterForeground() {
   // do what's needed
}

- (void)viewDidLoad
{
   [self appWillEnterForeground]; //register For Application Will enterForeground
}


- (id)appWillEnterForeground{ //Application will enter foreground.

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


-(void) allFunctions{ //call any functions that need to be run when application will enter foreground 
    NSLog(@"calling all functions...application just came back from foreground");


}