Question

我使用此功能删除然后在后台添加核心数据：

- (void) resetDatabase {
    count++;

    dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
        ConDAO *con = [[ConDAO alloc] init];
        DatabaseManager *manager = [DatabaseManager sharedManager];
        NSError * error;
        NSURL * storeURL = [[[manager managedObjectContext] persistentStoreCoordinator] URLForPersistentStore:[[[[manager managedObjectContext] persistentStoreCoordinator] persistentStores] lastObject]];
        [[manager managedObjectContext] reset];//to drop pending changes
        if ([[[manager managedObjectContext] persistentStoreCoordinator] removePersistentStore:[[[[manager managedObjectContext] persistentStoreCoordinator] persistentStores] lastObject] error:&error])
        {
            // remove the file containing the data
            [[NSFileManager defaultManager] removeItemAtURL:storeURL error:&error];
            //recreate the store like in the  appDelegate method
            [[[manager managedObjectContext] persistentStoreCoordinator] addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error];//recreates the persistent store
        }
        NSLog(@"*****************************");
        NSLog(@"updating");
        NSLog(@"count: %d", count);
        NSLog(@"*****************************");

        [self populateDatabase:0 con:con];


        NSTimer *timer = [NSTimer timerWithTimeInterval:60.0
                                                 target:self
                                               selector:@selector(resetDatabase)
                                               userInfo:nil repeats:NO];
        [[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
        dispatch_async(dispatch_get_main_queue(), ^(void){
            [self.view setNeedsDisplay];
// want to update view
            });
        });
    }

然后这段代码确保代码在后台运行时屏幕不会改变：

dispatch_async(dispatch_get_main_queue(), ^{
                if (count == 1) {
                [self performSegueWithIdentifier:@"load" sender:self];
                }
                else {
                    CardScanView *cardScan = [[CardScanView alloc]init];
                    [cardScan viewDidLoad];
                }
        });

然而，应用的某些部分无法加载，直到我在应用上打开另一个页面，然后返回并重试。

如果我不更改页面，也会收到此错误：

This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.

我该如何解决这个问题？

在后台更新核心数据时出错

0 个答案: