Photos(PHFetchResultChangeDetails)

Photos(PHChange)

Photos(PHObjectChangeDetails)

Photos(PHFetchResultChangeDetails)

PHFetchResultChangeDetails主要用于记录PHFetchResult的变动，这样可以同时判断多个数据是否有变动。

1 获取PHFetchResult

/// 变化前
public var fetchResultBeforeChanges: PHFetchResult { get }

/// 变化后
public var fetchResultAfterChanges: PHFetchResult { get }

2 获取变动信息

/// 是否有变动
public var hasIncrementalChanges: Bool { get }

/// 删除对象的位置
public var removedIndexes: NSIndexSet? { get }
/// 删除的对象
public var removedObjects: [PHObject] { get }

/// 插入对象的位置
public var insertedIndexes: NSIndexSet? { get }
/// 插入的对象
public var insertedObjects: [PHObject] { get }

/// 有变化的对象位置
public var changedIndexes: NSIndexSet? { get }
/// 有变化的对象
public var changedObjects: [PHObject] { get }

/// 移动照片
public func enumerateMovesWithBlock(handler: (Int, Int) -> Void)

/// 是否有移动
public var hasMoves: Bool { get }

3 比较PHFetchResult

/// 获取两个PHFetchResult的差异
///
/// - parameter fromResult : PHFetchResult
/// - parameter toResult : PHFetchResult
/// - parameter changedObjects : [PHObject]
///
/// - returns: PHFetchResultChangeDetails
public convenience init(fromFetchResult fromResult: PHFetchResult, toFetchResult toResult: PHFetchResult, changedObjects: [PHObject])

4 实战演练

func photoLibraryDidChange(changeInfo: PHChange!) {

    // Photos may call this method on a background queue;
    // switch to the main queue to update the UI.
    dispatch_async(dispatch_get_main_queue()) {

        // Check for changes to the displayed album itself
        // (its existence and metadata, not its member assets).
        if let albumChanges = changeInfo.changeDetailsForObject(self.displayedAlbum) {
            // Fetch the new album and update the UI accordingly.
            self.displayedAlbum = albumChanges.objectAfterChanges as PHAssetCollection
            self.navigationController.navigationItem.title = self.displayedAlbum.localizedTitle
        }

        // Check for changes to the list of assets (insertions, deletions, moves, or updates).
        if let collectionChanges = changeInfo.changeDetailsForFetchResult(self.assetsFetchResults) {

            // Get the new fetch result for future change tracking.
            self.assetsFetchResults = collectionChanges.fetchResultAfterChanges

            if collectionChanges.hasIncrementalChanges {

                // Get the changes as lists of index paths for updating the UI.
                var removedPaths: [NSIndexPath]?
                var insertedPaths: [NSIndexPath]?
                var changedPaths: [NSIndexPath]?
                if let removed = collectionChanges.removedIndexes {
                    removedPaths = self.indexPathsFromIndexSet(removed)
                }
                if let inserted = collectionChanges.insertedIndexes {
                    insertedPaths = self.indexPathsFromIndexSet(inserted)
                }
                if let changed = collectionChanges.changedIndexes {
                    changedPaths = self.indexPathsFromIndexSet(changed)
                }

                // Tell the collection view to animate insertions/deletions/moves
                // and to refresh any cells that have changed content.
                self.collectionView.performBatchUpdates(
                    {
                        if removedPaths {
                            self.collectionView.deleteItemsAtIndexPaths(removedPaths)
                        }
                        if insertedPaths {
                            self.collectionView.insertItemsAtIndexPaths(insertedPaths)
                        }
                        if changedPaths {
                            self.collectionView.reloadItemsAtIndexPaths(changedPaths)
                        }
                        if (collectionChanges.hasMoves) {
                            collectionChanges.enumerateMovesWithBlock() { fromIndex, toIndex in
                                let fromIndexPath = NSIndexPath(forItem: fromIndex, inSection: 0)
                                let toIndexPath = NSIndexPath(forItem: toIndex, inSection: 0)
                                self.collectionView.moveItemAtIndexPath(fromIndexPath, toIndexPath: toIndexPath)
                            }
                        }
                    }, completion: nil)
            } else {
                // Detailed change information is not available;
                // repopulate the UI from the current fetch result.
                self.collectionView.reloadData()
            }
        }
    }
}

其他

源代码

Swift

参考资料

Photos Framework Reference

PHChange Class Reference

PHFetchResultChangeDetails Class Reference

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