NSTimer *上的选择器可以在后台执行吗？

Question

具体来说，我正着眼于后台应用程序收到位置服务更新（重大位置更改）的情况。在这种情况下，背景会发生什么？任何用户代码都可以运行，包括待定计时器吗？

Answer 1

你可以像下面使用后台任务和定时器：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
    { 
     // Override point for customization after application launch. 
     self.locationManager = [[CLLocationManager alloc] init]; 
     self.locationManager.delegate = self; 

     [self.locationManager startUpdatingLocation]; 
     return YES; 
    } 

- (void)applicationDidEnterBackground:(UIApplication *)application 
{ 

    self.bgTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{ 


     [[UIApplication sharedApplication] endBackgroundTask:self.bgTask]; 
     self.bgTask = UIBackgroundTaskInvalid; 
    }]; 


    self.timer = [NSTimer scheduledTimerWithTimeInterval:60 
                target:self 
               selector:@selector(changeAccuracy) 
               userInfo:nil 
               repeats:YES]; 
} 


- (void) changeAccuracy { 
    [self.locationManager setDesiredAccuracy:kCLLocationAccuracyBest]; 
    [self.locationManager setDistanceFilter:kCLDistanceFilterNone]; 
} 

-(void)locationManager:(CLLocationManager *)lm didUpdateLocations:(NSArray *)locations{ 
    CLLocation *location = [locations lastObject]; 

    NSLog(@"Location returned: %f, %f Accuracy: %f", location.coordinate.latitude, location.coordinate.longitude, location.horizontalAccuracy); 
    [lm setDesiredAccuracy:kCLLocationAccuracyThreeKilometers]; 
    [lm setDistanceFilter:99999]; 
}