Detect iOS App Entering Background

Detect iOS app entering background

You can add an observer to your view controller:

edit/update: Xcode 11 • Swift 5

iOS13 or later

UIScene.willDeactivateNotification

iOS12 or earlier

UIApplication.willResignActiveNotification

---

if #available(iOS 13.0, *) {
    NotificationCenter.default.addObserver(self, selector: #selector(willResignActive), name: UIScene.willDeactivateNotification, object: nil)
} else {
    NotificationCenter.default.addObserver(self, selector: #selector(willResignActive), name: UIApplication.willResignActiveNotification, object: nil)
}

and add a selector method to your view controller that will be executed when your app receives that notification:

@objc func willResignActive(_ notification: Notification) {
    // code to execute
}

What's the best way to detect when the app is entering the background for my view?

You can have any class interested in when the app goes into the background receive notifications. This is a good alternative to coupling these classes with the AppDelegate.

When initializing said classes:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillResignActive:) name:UIApplicationWillResignActiveNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillTerminate:) name:UIApplicationWillTerminateNotification object:nil];

Responding to the notifications

-(void)appWillResignActive:(NSNotification*)note
{

}
-(void)appWillTerminate:(NSNotification*)note
{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillResignActiveNotification object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillTerminateNotification object:nil];

}

swift - How to detect from what ViewController application enter background?

On AppDelegate Methods: applicationDidEnterBackground or applicationWillEnterForeground, you can get the top most UIViewController. It is well explained on this question: Get top most UIViewController

Detect if the application in background or foreground in swift

[UIApplication sharedApplication].applicationState will return current state of applications such as:

• UIApplicationStateActive
• UIApplicationStateInactive
• UIApplicationStateBackground

or if you want to access via notification see UIApplicationDidBecomeActiveNotification

Swift 3+

let state = UIApplication.shared.applicationState
if state == .background || state == .inactive {
    // background
} else if state == .active {
    // foreground
}

switch UIApplication.shared.applicationState {
    case .background, .inactive:
        // background
    case .active:
        // foreground
    default:
        break
}

Objective C

UIApplicationState state = [[UIApplication sharedApplication] applicationState];
if (state == UIApplicationStateBackground || state == UIApplicationStateInactive) {
    // background
} else if (state == UIApplicationStateActive) {
    // foreground
}

Detect when a view controller goes to background and gets resumed

use UIApplicationDidBecomeActive for resume and UIApplicationWillResignActive for handle goes background

SwiftUI

Text("check application state!")
                .onReceive(NotificationCenter.default.publisher(for: UIApplication.willResignActiveNotification)) { _ in
                    print("User received on  willResignActiveNotification!")
                }
                .onReceive(NotificationCenter.default.publisher(for: UIApplication.didBecomeActiveNotification)) { _ in
                    print("User received on  didBecomeActiveNotification!")
                }

Swift 5.x > above

override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        NotificationCenter.default.removeObserver(self, name: UIApplication.willResignActiveNotification, object: nil)
        NotificationCenter.default.removeObserver(self, name:  UIApplication.didBecomeActiveNotification, object: nil)
    }

override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver(self, selector: #selector(self.openAndCloseActivity), name: UIApplication.willResignActiveNotification, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(self.openAndCloseActivity), name: UIApplication.didBecomeActiveNotification, object: nil)
}

@objc func openAndCloseActivity(_ notification: Notification)  {
    if notification.name == UIApplication.didBecomeActiveNotification{
        // become active notifictaion
    }else{
        // willResignActiveNotification
    }
    
}

Swift 5.x < below

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIApplicationWillResignActive, object: nil)
     NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIApplicationDidBecomeActive, object: nil)
}

override func viewDidLoad() {
    super.viewDidLoad()
    
    NotificationCenter.default.addObserver(self, selector: #selector(self.closeActivityController), name: NSNotification.Name.UIApplicationWillResignActive, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(self.openactivity), name: NSNotification.Name.UIApplicationDidBecomeActive, object: nil)
   
    
}

and handle the method as

func closeActivityController()  {
    
    
}

func openactivity()  {
    
    //view should reload the data.
}

other notification types are

extension NSNotification.Name { 
@available(iOS 4.0, *)
public static let UIApplicationDidEnterBackground: NSNotification.Name

@available(iOS 4.0, *)
public static let UIApplicationWillEnterForeground: NSNotification.Name

public static let UIApplicationDidFinishLaunching: NSNotification.Name

public static let UIApplicationDidBecomeActive: NSNotification.Name

public static let UIApplicationWillResignActive: NSNotification.Name

public static let UIApplicationDidReceiveMemoryWarning: NSNotification.Name

public static let UIApplicationWillTerminate: NSNotification.Name

}

xamarin.forms detect ios app entering foreground from background

In native Xamarin.iOS app, there is a method
WillEnterForegroundNotification but this method is not available here.

You can access WillEnterForegroundNotification method in Xamarin.forms project, just override it in AppDelegate.cs:

public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
    //
    // This method is invoked when the application has loaded and is ready to run. In this 
    // method you should instantiate the window, load the UI into it and then make the window
    // visible.
    //
    // You have 17 seconds to return from this method, or iOS will terminate your application.
    //
    public override bool FinishedLaunching(UIApplication app, NSDictionary options)
    {
        global::Xamarin.Forms.Forms.Init();
        LoadApplication(new App());

        return base.FinishedLaunching(app, options);
    }

    public override void WillEnterForeground(UIApplication uiApplication)
    {   
        //handle your event here 
        base.WillEnterForeground(uiApplication);
    }
} 

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