1

我在尝试在PHChange事件发生后更改我的数据源时遇到问题。我正在使用一个NSMutableOrderedSet作为我的数据源类型。当 aPHChange发生时，它可以返回三个可能的索引：removedIndexes、insertedIndexes和changedIndexes。

问题是我不确定如何在先前的数据源中反映这些变化。有人可以解释一下我如何转换中给出的索引PHChange来更新我的recentsCollectionDataSource. 我UICollectionView用作recentsCollectionDataSource它的数据源。

现在我在想唯一的方法是手动枚举和构建我自己更改的索引，而不是使用PHFetchResultChangeDetails那些。

我将不胜感激提供的任何帮助。也欢迎任何有关制作我的数据源的替代方法的建议。

代码：

@property (nonatomic, strong) PHFetchResult *assetsFetchResult;
@property (nonatomic, strong) NSMutableOrderedSet *recentsCollectionDataSource;

- (void)setup
{
    self.recentsCollectionDataSource = [[NSMutableOrderedSet alloc]init];

    self.assetsFetchResult = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum | PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAny options:nil];

    for (PHAssetCollection *sub in self.assetsFetchResult)
    {
        PHFetchResult *assetsInCollection = [PHAsset fetchAssetsInAssetCollection:sub options:nil];

        for (PHAsset *asset in assetsInCollection)
        {
            [self.recentsCollectionDataSource addObject:asset];
        }
    }

    if (self.recentsCollectionDataSource.count > 0)
    {
        NSArray *array = [self.recentsCollectionDataSource sortedArrayUsingDescriptors:@[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:NO]]];

        self.recentsCollectionDataSource = [[NSMutableOrderedSet alloc]initWithArray:array];
    }
}

- (void)photoLibraryDidChange:(PHChange *)changeInstance
{
    PHFetchResultChangeDetails *collectionChanges = [changeInstance changeDetailsForFetchResult:self.assetsFetchResult];

    if (collectionChanges)
    {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0),^
        {
            self.assetsFetchResult = [collectionChanges fetchResultAfterChanges];

            if (!collectionChanges.hasIncrementalChanges || collectionChanges.hasMoves)
            {
                dispatch_async(dispatch_get_main_queue(),^
                {
                    [self.recentsCollectionView reloadData];
                });
            }
            else
            {
                dispatch_async(dispatch_get_main_queue(),^
                {
                    [self.recentsCollectionView performBatchUpdates:^
                     {
                         NSIndexSet *removedIndexes = [collectionChanges removedIndexes];
                         NSIndexSet *insertedIndexes = [collectionChanges insertedIndexes];
                         NSIndexSet *changedIndexes = [collectionChanges changedIndexes];

                         // Need to update our old recentsCollectionDataSource
                         // somehow, otherwise we get a crash.

                         if (removedIndexes.count)
                         {
                             [self.recentsCollectionView deleteItemsAtIndexPaths:[removedIndexes indexPathsFromIndexesWithSection:0]];
                         }

                         if (insertedIndexes.count)
                         {
                             [self.recentsCollectionView insertItemsAtIndexPaths:[insertedIndexes indexPathsFromIndexesWithSection:0]];
                         }

                         if (changedIndexes.count)
                         {
                             [self.recentsCollectionView reloadItemsAtIndexPaths:[changedIndexes indexPathsFromIndexesWithSection:0]];
                         }
                     }completion:NULL];
                });
            }
        });
    }
}

@implementation NSIndexSet (Convenience)

- (NSArray *)indexPathsFromIndexesWithSection:(NSUInteger)section
{
    NSMutableArray *indexPaths = [NSMutableArray arrayWithCapacity:self.count];

    [self enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop)
    {
        [indexPaths addObject:[NSIndexPath indexPathForItem:idx inSection:section]];
    }];
    return indexPaths;
}

@end
4

1 回答 1

0

我似乎已经解决了（至少现在）。我分别构建了自己的删除、插入和更改索引，这不如内置索引那么有效PHFetchResultChangeDetails，但我不相信还有其他方法可以做到这一点。使用此代码在 iPhone 5 上浏览 2600 张照片大约需要 4 秒，所以没有想象中那么糟糕。

我注意到可能是一个错误PHFetchResultChangeDetails，它不会将收藏夹更改放在更改详细信息中，因此如果您想在 UI 中保持视觉一致，不妨再次执行整个集合提取。

代码：

- (void)photoLibraryDidChange:(PHChange *)changeInstance
{
    PHFetchResultChangeDetails *collectionChanges = [changeInstance changeDetailsForFetchResult:self.assetsFetchResult];

    if (collectionChanges)
    {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0),^
        {
            self.assetsFetchResult = [collectionChanges fetchResultAfterChanges];

            NSMutableOrderedSet *newSet = [[NSMutableOrderedSet alloc]init];

            for (PHAssetCollection *sub in self.assetsFetchResult)
            {
                PHFetchResult *assetsInCollection = [PHAsset fetchAssetsInAssetCollection:sub options:nil];

                for (PHAsset *asset in assetsInCollection)
                {
                    [newSet addObject:asset];
                }
            }

            NSMutableIndexSet *removedIndexes = [[NSMutableIndexSet alloc]init];
            NSMutableIndexSet *insertedIndexes = [[NSMutableIndexSet alloc]init];
            NSMutableIndexSet *changedIndexes = [[NSMutableIndexSet alloc]init];

            NSMutableArray *objectsToInsert = [[NSMutableArray alloc]init];

            if (newSet.count > 0)
            {
                NSArray *array = [newSet sortedArrayUsingDescriptors:@[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:NO]]];

                newSet = [[NSMutableOrderedSet alloc]initWithArray:array];

                for (id obj in newSet)
                {
                    NSUInteger idx = [self.recentsCollectionDataSource indexOfObject:obj];

                    if (idx == NSNotFound)
                    {
                        [objectsToInsert addObject:obj];

                        [insertedIndexes addIndex:[newSet indexOfObject:obj]];
                    }
                    else
                    {
                        NSUInteger objIdx = [newSet indexOfObject:obj];

                        PHAsset *oldAssetToCompare = (PHAsset *)[self.recentsCollectionDataSource objectAtIndex:idx];
                        PHAsset *plausibleNewAssetToCompare = (PHAsset *)[newSet objectAtIndex:objIdx];

                        if (![oldAssetToCompare isEqual:plausibleNewAssetToCompare])
                        {
                            [changedIndexes addIndex:idx];
                        }
                    }
                }

                for (id obj in self.recentsCollectionDataSource)
                {
                    NSUInteger idx = [newSet indexOfObject:obj];

                    if (idx == NSNotFound)
                    {
                        [removedIndexes addIndex:[self.recentsCollectionDataSource indexOfObject:obj]];
                    }
                    else
                    {
                        NSUInteger objIdx = [self.recentsCollectionDataSource indexOfObject:obj];

                        PHAsset *oldAssetToCompare = (PHAsset *)obj;
                        PHAsset *plausibleNewAssetToCompare = (PHAsset *)[newSet objectAtIndex:idx];

                        if (![oldAssetToCompare isEqual:plausibleNewAssetToCompare])
                        {
                            [changedIndexes addIndex:objIdx];
                        }
                    }
                }
            }

            if (removedIndexes.count > 0)
            {
                [self.recentsCollectionDataSource removeObjectsAtIndexes:removedIndexes];
            }

            if (insertedIndexes.count > 0)
            {
                [self.recentsCollectionDataSource insertObjects:objectsToInsert atIndexes:insertedIndexes];
            }

            if (!collectionChanges.hasIncrementalChanges || collectionChanges.hasMoves)
            {
                dispatch_async(dispatch_get_main_queue(),^
                {
                    [self.recentsCollectionView reloadData];
                });
            }
            else
            {
                dispatch_async(dispatch_get_main_queue(),^
                {
                    [self.recentsCollectionView performBatchUpdates:^
                     {
                         if (removedIndexes.count > 0)
                         {
                             [self.recentsCollectionView deleteItemsAtIndexPaths:[removedIndexes indexPathsFromIndexesWithSection:0]];
                         }

                         if (insertedIndexes.count > 0)
                         {
                             [self.recentsCollectionView insertItemsAtIndexPaths:[insertedIndexes indexPathsFromIndexesWithSection:0]];
                         }

                         if (changedIndexes.count > 0)
                         {
                             [self.recentsCollectionView reloadItemsAtIndexPaths:[changedIndexes indexPathsFromIndexesWithSection:0]];
                         }
                     }completion:NULL];
                });
            }
        });
    }
}
于 2015-06-03T05:05:53.957 回答