我需要在后台和前台完成一项长时间运行的任务。这会更新核心数据。因此，为了保持 UI 响应，我创建了另一个线程，在其中使用不同的 managedObjectContext(MOC)。因此，在后台和前台都设置了一个计时器，并在状态更改时适当地停用。在任务开始之前和任务完成之后，当我按下主页按钮时，它会正确调用两个委托方法，但是当我按下主页按钮屏幕更改和 UI 挂起（变为空白）时任务处于活动状态但两个委托方法不是正确调用并且应用程序不会终止。我找不到发生这种情况的原因。如果有人可以提供帮助，那将很有帮助。
我将附上所需的代码：
-(void) startTimerThread
{
dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
// Add code here to do background processing
NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
[context setPersistentStoreCoordinator:[(AppDelegate *)[[UIApplication sharedApplication] delegate] persistentStoreCoordinator]];
self.managedObjectContext = context;
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(mergeChanges:)
name:NSManagedObjectContextDidSaveNotification
object:context];
NSLog(@"managedObjContext : %@\n",self.managedObjectContext);
[self getDataFromFile];
dispatch_async( dispatch_get_main_queue(), ^{
// Add code here to update the UI/send notifications based on the
// results of the background processing
[[NSNotificationCenter defaultCenter] postNotificationName:@"ReloadAppDelegateTable" object:nil];
[context release];
[[NSNotificationCenter defaultCenter] removeObserver:self
name:NSManagedObjectContextDidSaveNotification
object:context];
});
});
}
- (void)applicationDidEnterBackground:(UIApplication *)application
{
NSLog(@"Background\n");
[self.notificationTimer invalidate];
self.notificationTimer = nil;
UIApplication *app = [UIApplication sharedApplication];
self.bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
[app endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
//start location update timer and background timer
self.timer = [NSTimer scheduledTimerWithTimeInterval:180 target:self
selector:@selector(startLocationServices) userInfo:nil repeats:YES];
self.locationManager.delegate = self;
[self.locationManager startUpdatingLocation];
self.logDownloader.managedObjectContext = self.managedObjectContext;
NSLog(@"managedObjContext : %@\n",self.logDownloader.managedObjectContext);
self.backgroundTimer = [NSTimer scheduledTimerWithTimeInterval:90 target:self.logDownloader selector:@selector(getDataFromFile) userInfo:nil repeats:YES];
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
NSLog(@"Foreground\n");
//invalidate background timer and location update timer
[self.timer invalidate];
[self.backgroundTimer invalidate];
self.timer = nil;
self.notificationTimer = nil;
self.logDownloader.managedObjectContext = self.managedObjectContext;
NSLog(@"managedObjContext : %@\n",self.logDownloader.managedObjectContext);
[[NSNotificationCenter defaultCenter] postNotificationName:@"ReloadAppDelegateTable" object:nil];
self.notificationTimer = [NSTimer scheduledTimerWithTimeInterval:180 target:self.logDownloader selector:@selector(startTimerThread) userInfo:nil repeats:YES];
}