Swift - 检测应用程序何时发送到后台但不是设备被锁定时

Question

I'm in the process of developing an iOS app where I need to track if the user leaves the app (presses the home button to use other apps) while they are 'in game' however the user should be able to lock and un-lock their device without this function being called.

func applicationDidEnterBackground(application: UIApplication) {

    if defaults.boolForKey("TimerActive"){
        defaults.setBool(true, forKey: "Failed")
    }
}

This, unfortunately, is triggered when the user locks their devices as well as when they exit the app.

A little context about the app: The app encourages people to focus on their work and not become distracted by their phones for a preset time period. Other suggestions of how I can encourage the users to reopen the app upon exit while the timer is still active but not when they lock their devices would be greatly welcomed!

Answer 1

Well, there's no clean way to do this. But there is a hack that you can use. It's not guaranteed to keep working though(I've tested up to iOS 9.3 and I'm pretty sure it works on the iOS 10 betas).

The idea is that there's a system-wide notification for the phone being locked. You can listen to that and coupled with listening to background/foreground events on your app you can determine what's happening.

This is a piece of code for an object that will watch for this stuff. Create it from app delegate or wherever and keep a strong ref for as long as you need it. Give it a delegate it can call for whatever events you want to observer and react to(or put the code right there in checkState ). I haven't compiled this so I may have made some errors typing it up. It's derived from code I use in an app, but the original has a lot more stuff I won't post here. It's in objc but it shouldn't be too hard to convert to swift(someone feel free to post a second answer in swift or edit mine, but I don't have the time to do it right now)

@interface LockStateDetector : NSObject {
    int _notify_token;
}

@property BOOL deviceIsLocked;
@property BOOL appIsInBackground;
@property NSTimer * checkStateTimer;

@end

@implementation LockStateDetector

- (instancetype)init
{
    self = [super init];
    if (self) {
       [self registerForNotifications];
    }
    return self;
}

- (void)dealloc
{
   [[NSNotificationCenter defaultCenter] removeObserver:self];
   notify_cancel(_notify_token);
}

- (void)registerForNotifications
{
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didMoveToBackground) name:UIApplicationDidEnterBackgroundNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didBecomeActive) name:UIApplicationDidBecomeActiveNotification object:nil];
    __weak__ LockStateDector * wSelf = self;
    notify_register_dispatch("com.apple.springboard.lockstate", &_notify_token, dispatch_get_main_queue(), ^(int token) {
        __strong__ LockStateDetector sSelf = wSelf;
        if (!sSelf) { 
            return;
        }
        uint64_t state = UINT64_MAX;
        notify_get_state(token, &state);
        sSelf.deviceIsLocked = state != 0;
        NSLog(@"device lock state changed: %@", @(state));
        [sSelf checkState];
    });
}

- (void)didBecomeActive
{
    self.appIsInBackground = NO;
    [self checkState];
}

- (void)didMoveToBackground
{
    self.appIsInBackground = YES;
    [self checkState];
}

- (void)checkState
{
    [self.checkStateTimer invalidate];
    self.checkStateTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(_checkState) userInfo:nil repeats:NO];
}

- (void)_checkState
{
    [self.checkStateTimer invalidate];
    self.checkStateTimer = nil;

    if (!self.appIsInBackground) {
        return;
    }

    if (!self.deviceIsLocked) {
        // app is in background because device was locked
    } else {
       // app is in background because user pressed home and switched to something else
    }

}