ios - 在操作 block 中具有单独的Realm实例时，“从错误的线程访问了Realm”

Question

我在单独的后台操作中更新领域对象，并在操作块本身中创建了Realm实例，但仍然收到此错误。有什么线索吗？

- (void)didFavoriteButtonTapped:(FlickerPhotoCell *)photoCell {

NSIndexPath *indexPath = [self.collectionView indexPathForCell:photoCell];
FlickerPhoto *photo = [self.photos objectAtIndex:indexPath.item];
photoCell.photoFavouriteButton.selected = !photo.isFavorited;

[self.opQueue addOperationWithBlock:^{

    RLMRealm *realm = [RLMRealm defaultRealm];
    [realm beginWriteTransaction];
    photo.isFavorited = !photo.isFavorited;
    [realm commitWriteTransaction];

    //Saving in local database
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"photoURL == %@ AND isFavorited == YES", photo.photoURL];
    RLMResults *searchedPhotos = [FlickerPhoto objectsWithPredicate:pred];
    FlickerPhoto *photoInDatabase = [searchedPhotos firstObject];
    BOOL isPhotoExists = (photoInDatabase != nil);

    if(photo.isFavorited) {
        if(!isPhotoExists) {
            [realm transactionWithBlock:^{
                [realm addObject:photo];
            }];
        }
    } else {
        if(isPhotoExists) {
            [realm beginWriteTransaction];
            [realm deleteObject:photoInDatabase];
            [realm commitWriteTransaction];
        }
    }
}];

}

Answer 1

境界不安全。因此，只要您想写入Realm，它就必须与您创建对象的线程相同。
因此，在开始“addOperationWithBlock”操作之前，应该获取要访问的对象的唯一标识符，然后从该操作块中创建它。

因此，您可以执行以下三种选择之一:

在同一线程上更新领域对象，顺便说一句，根据我的经验，这已经足够好了，领域写入事务并不是一项非常昂贵的任务。但这又取决于该调用的频率。

在新线程中再次创建对象，并传递唯一的标识符而不是领域对象本身，然后在要写入的线程上重新创建它:

- (void)didFavoriteButtonTapped:(FlickerPhotoCell *)photoCell {


 NSIndexPath *indexPath = [self.collectionView indexPathForCell:photoCell];
    FlickerPhoto *photo = [self.photos objectAtIndex:indexPath.item];
    NSString *photoUniqueIdentifier = photo.id // Getting I'ts identifier before opening a new thread 
    photoCell.photoFavouriteButton.selected = !photo.isFavorited;

    [self.opQueue addOperationWithBlock:^{

    FlickerPhoto *photoToUpdate = [FlickerPhoto objectForPrimaryKey:photoUniqueIdentifier]; // Getting the object again from the data base, in the new thread contex

    RLMRealm *realm = [RLMRealm defaultRealm];
    [realm beginWriteTransaction];
    photoToUpdate.isFavorited = !photoToUpdate.isFavorited;
    [realm commitWriteTransaction];

    //Saving in local database
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"photoURL == %@ AND isFavorited == YES", photoToUpdate.photoURL];
    RLMResults *searchedPhotos = [FlickerPhoto objectsWithPredicate:pred];
    FlickerPhoto *photoInDatabase = [searchedPhotos firstObject];
    BOOL isPhotoExists = (photoInDatabase != nil);

    if(photoToUpdate.isFavorited) {
        if(!isPhotoExists) {
            [realm transactionWithBlock:^{
                [realm addObject:photoToUpdate];
            }];
        }
    } else {
        if(isPhotoExists) {
            [realm beginWriteTransaction];
            [realm deleteObject:photoInDatabase];
            [realm commitWriteTransaction];
        }
    }
}];

或者您可以使用alloc init创建它，并手动设置I唯一标识符(不是写事务)，然后可以从任何线程访问它，因为我还不是数据库对象。