我有一个UICollectionView，可以显示用户的照片库图片。我允许用户选择多张照片，经过一些处理后，我将更改后的照片作为新照片保存到照片库（不删除旧照片）。我使用这种方法保存照片：
fileprivate func saveImagesToLibrary(imageArray:[UIImage]){
var savedImageNum = 0
let increment = 0.8 / Float(imageArray.count)
var percentage:Float = 0.2
self.getAlbumWithName(name: albumNameToCreate) { (assetCollection) in
if let collection = assetCollection {
let group = DispatchGroup()
for (_,image) in imageArray.enumerated(){
group.enter()
PHPhotoLibrary.shared().performChanges({
let request = PHAssetChangeRequest.creationRequestForAsset(from: image)
let placeholder = request.placeholderForCreatedAsset
let albumChangeRequest = PHAssetCollectionChangeRequest(for: collection)
if let placeholder = placeholder, let albumChangeRequest = albumChangeRequest {
albumChangeRequest.addAssets([placeholder] as NSArray)
}
}, completionHandler: { (success, error) in
DispatchQueue.main.async {
percentage = percentage+increment
SVProgressHUD.showProgress(Float(percentage), status: "Saving photos...")
}
group.leave()
if success == true {
savedImageNum += 1
} else {
if let inError = error {
print(inError)
}
}
})
}
group.notify(queue: .main, execute: {
var status = ""
if savedImageNum == 0 {
self.dismissProgressHUDWithError()
} else if savedImageNum == 1 {
status = "Saved \(savedImageNum) image out of \(self.selectedAssets.count) in \"Saved from Xif\" album"
SVProgressHUD.showSuccess(withStatus: status)
SVProgressHUD.dismiss(withDelay: 3)
self.view.isUserInteractionEnabled = true
self.removeAllSelections()
self.dismissDimmerView()
} else {
status = "Saved \(savedImageNum) images out of \(self.selectedAssets.count) in \"Saved from Xif\" album"
SVProgressHUD.showSuccess(withStatus: status)
SVProgressHUD.dismiss(withDelay: 3)
self.view.isUserInteractionEnabled = true
self.removeAllSelections()
self.dismissDimmerView()
}
})
} else {
DispatchQueue.main.async {
self.dismissProgressHUDWithError()
}
}
}
}
如上所述，我使用removeAllSelections（）取消选择所有单元格：
fileprivate func removeAllSelections(){
selectedAssets = []
disableDeleteButton()
photoCollectionView.reloadData()
}
我也在代码的其他地方使用removeAllSelections（），并且一切正常，但是当我在saveImagesToLibrary方法中使用它时，有时无法删除选择。似乎reloadDeta（）命令无法正常运行，因为它与PHPhotoLibraryChangeObserver调用冲突，该调用也尝试更新集合视图：
extension centerViewController: PHPhotoLibraryChangeObserver {
func photoLibraryDidChange(_ changeInstance: PHChange) {
guard let changes = changeInstance.changeDetails(for: inFetchResult)
else { return }
// Change notifications may originate from a background queue.
// As such, re-dispatch execution to the main queue before acting
// on the change, so you can update the UI.
DispatchQueue.main.sync {
// Hang on to the new fetch result.
inFetchResult = changes.fetchResultAfterChanges
updateSelectedAssetsAfterChange()
// If we have incremental changes, animate them in the collection view.
if changes.hasIncrementalChanges {
guard let collectionView = self.photoCollectionView else { fatalError() }
// Handle removals, insertions, and moves in a batch update.
collectionView.performBatchUpdates({
if let removed = changes.removedIndexes, !removed.isEmpty {
collectionView.deleteItems(at: removed.map({ IndexPath(item: $0, section: 0) }))
}
if let inserted = changes.insertedIndexes, !inserted.isEmpty {
collectionView.insertItems(at: inserted.map({ IndexPath(item: $0, section: 0) }))
}
changes.enumerateMoves { fromIndex, toIndex in
collectionView.moveItem(at: IndexPath(item: fromIndex, section: 0),
to: IndexPath(item: toIndex, section: 0))
}
})
// We are reloading items after the batch update since `PHFetchResultChangeDetails.changedIndexes` refers to
// items in the *after* state and not the *before* state as expected by `performBatchUpdates(_:completion:)`.
if let changed = changes.changedIndexes, !changed.isEmpty {
collectionView.reloadItems(at: changed.map({ IndexPath(item: $0, section: 0) }))
}
} else {
// Reload the collection view if incremental changes are not available.
photoCollectionView.reloadData()
}
resetCachedAssets()
updateFooter()
}
}
}
我尝试将removeAllSelections（）放在photoLibraryDidChange（）中，但由于多次调用photoLibraryDidChange（）而无法解决问题，因此无法找出何时完全完成所有任务。任何帮助表示赞赏。