iOS:核心数据 performBlock 使 UI 无响应

Question

我只是想弄清楚核心数据私有(private)上下文。我正在尝试使用私有(private)上下文 (NSPrivateQueueConcurrencyType) 插入 20k 记录。但是只要点击“插入 20k 记录”按钮，UI 线程就会挂起。

- (IBAction)insertRecords:(id)sender {


[[CoreDataStore privateContext] performBlock:^{

    NSLog(@"Starting to insert 20k records...");
    for (int i = 0 ; i < 20000; i++)
    {
        NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:@"Event" inManagedObjectContext:[CoreDataStore privateContext]];
        [newManagedObject setValue:[NSDate date] forKey:@"time"];
    }
    NSError * error = nil;
    NSLog(@"Inserted 20k records to managed object context");
    [[CoreDataStore privateContext] save:&error];
    NSLog(@"Save context command fired");

}];

NSLog(@"returning from insert method");
}

私有(private)上下文的更改正在此处合并到主上下文

- (void)contextDidSavePrivateQueueContext:(NSNotification *)notification
{
    @synchronized(self) {

    [self.mainContext performBlock:^{
        NSLog(@"merging changes to main context.....");
        [self.mainContext mergeChangesFromContextDidSaveNotification:notification];
        NSLog(@"merged changes to main context");
    }];
}
}

下面是我点击插入按钮时的日志窗口输出:

2014-08-04 14:54:12.431 CoreDataDrillDown[11323:90b] returning from insert method
2014-08-04 14:54:12.431 CoreDataDrillDown[11323:1403] Starting to insert 20k records...
2014-08-04 14:54:12.506 CoreDataDrillDown[11323:1403] Inserted 20k records to managed object context
2014-08-04 14:54:12.785 CoreDataDrillDown[11323:90b] merging changes to main context.....
2014-08-04 14:54:12.786 CoreDataDrillDown[11323:1403] Save context command fired
2014-08-04 14:54:27.019 CoreDataDrillDown[11323:90b] merged changes to main context

用户界面超过 15 秒没有响应。我想知道为什么？

使用以下方法建议 https://stackoverflow.com/users/817182/thom-ek和 https://stackoverflow.com/users/2128900/micha%c5%82-ciuba ，插入速度很快，不会卡住 UI，但更改不会保存到磁盘，不知道为什么。

//writerContext has persistent store coordinator, so it should write data to disk but it 
//is not writing any changes to disk.???????
 -(NSManagedObjectContext *)writerContext
    {
      if (!_writerContext)
    {
        _writerContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        _writerContext.persistentStoreCoordinator  =  [(AppDelegate *)[[UIApplication sharedApplication] delegate] persistentStoreCoordinator];
    }
    return _writerContext;
}
//mainContext is being used with NSFetchedResultController
-(NSManagedObjectContext *)mainContext
{
    if (!_mainContext)
    {
        _mainContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        _mainContext.parentContext = [self writerContext];
    }
    return _mainContext;
}

//performBlock is being called on privateContext
-(NSManagedObjectContext *)privateContext
{
    if (!_privateContext)
    {
        _privateContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        _privateContext.parentContext = [self mainContext];
    }
    return _privateContext;
}

Answer 1

主要问题是 mainContext 仍然绑定(bind)到 mainQueue，所以它将等待这个巨大的合并。

有关于异步保存的好文章:关于 Cocoanetics和 ObjC.io .

其他解决方案只是重置 mainContext 并重新加载所有 tableView(您不会一次向用户显示所有 20k 条记录)。