I'm learning Swift/SwiftUI by building a photo organizer app. It displays a user's photo library in a grid like the built-in photos app, and there's a detail view where you can do things like favorite a photo or add it to the trash.
My app loads all the data and displays it fine, but the UI doesn't update when things change. I've debugged enough to confirm that my edits are applied to the underlying PHAssets and Core Data assets. It feels like the problem is that my views aren't re-rendering.
I used Dave DeLong's approach to create an abstraction layer that separates Core Data from SwiftUI. I have a singleton environment object called DataStore that handles all interaction with Core Data and the PHPhotoLibrary. When the app runs, the DataStore is created. It makes an AssetFetcher that grabs all assets from the photo library (and implements PHPhotoLibraryChangeObserver). DataStore iterates over the assets to create an index in Core Data. My views' viewmodels query core data for the index items and display them using the @Query property wrapper from Dave's post.
App.swift
@main
struct LbPhotos2App: App {
var body: some Scene {
WindowGroup {
ContentView()
.environment(\.dataStore, DataStore.shared)
}
}
}
PhotoGridView.swift (this is what contentview presents)
struct PhotoGridView: View {
@Environment(\.dataStore) private var dataStore : DataStore
@Query(.all) var indexAssets: QueryResults<IndexAsset>
@StateObject var vm = PhotoGridViewModel()
func updateVm() {
vm.createIndex(indexAssets)
}
var body: some View {
GeometryReader { geo in
VStack {
HStack {
Text("\(indexAssets.count) assets")
Spacer()
TrashView()
}.padding(EdgeInsets(top: 4, leading: 16, bottom: 4, trailing: 16))
ScrollView {
ForEach(vm.sortedKeys, id: \.self) { key in
let indexAssets = vm.index[key]
let date = indexAssets?.first?.creationDate
GridSectionView(titleDate:date, indexAssets:indexAssets!, geoSize: geo.size)
}
}.onTapGesture {
updateVm()
}
}.onAppear {
updateVm()
}
.navigationDestination(for: IndexAsset.self) { indexAsset in
AssetDetailView(indexAsset: indexAsset)
}
}
}
}
PhotoGridViewModel.swift
class PhotoGridViewModel: ObservableObject {
@Published var index: [String:[IndexAsset]] = [:]
var indexAssets: QueryResults<IndexAsset>?
func createIndex() {
guard let assets = self.indexAssets else {return}
self.createIndex(assets)
}
func createIndex(_ queryResults: QueryResults<IndexAsset>) {
indexAssets = queryResults
if queryResults.count > 0 {
var lastDate = Date.distantFuture
for i in 0..<queryResults.count {
let item = queryResults[i]
let isSameDay = isSameDay(firstDate: lastDate, secondDate: item.creationDate!)
if isSameDay {
self.index[item.creationDateKey!]?.append(item)
} else {
self.index[item.creationDateKey!] = [item]
}
lastDate = item.creationDate!
}
}
self.objectWillChange.send()
}
var sortedKeys: [String] {
return index.keys.sorted().reversed()
}
private func isSameDay(firstDate:Date, secondDate:Date) -> Bool {
return Calendar.current.isDate(
firstDate,
equalTo: secondDate,
toGranularity: .day
)
}
}
Here's where I actually display the asset in GridSectionView.swift
LazyVGrid(columns: gridLayout, spacing: 2) {
let size = geoSize.width/4
ForEach(indexAssets, id:\.self) { indexAsset in
NavigationLink(
value: indexAsset,
label: {
AssetCellView(indexAsset: indexAsset, geoSize:geoSize)
}
).frame(width: size, height: size)
.buttonStyle(.borderless)
}
}
AssetCellView.swift
struct AssetCellView: View {
@StateObject var vm : AssetCellViewModel
var indexAsset : IndexAsset
var geoSize : CGSize
init(indexAsset: IndexAsset, geoSize: CGSize) {
self.indexAsset = indexAsset
self.geoSize = geoSize
_vm = StateObject(wrappedValue: AssetCellViewModel(indexAsset: indexAsset, geoSize: geoSize))
}
var body: some View {
ZStack(alignment: .bottomTrailing) {
if (vm.indexAsset != nil && vm.image != nil) {
vm.image?
.resizable()
.aspectRatio(contentMode: .fit)
.border(.blue, width: vm.indexAsset!.isSelected ? 4 : 0)
}
if (vm.indexAsset != nil && vm.indexAsset!.isFavorite) {
Image(systemName:"heart.fill")
.resizable()
.frame(width: 20, height: 20)
.foregroundStyle(.ultraThickMaterial)
.shadow(color: .black, radius: 12)
.offset(x:-8, y:-8)
}
}
}
}
AssetCellViewModel.swift
class AssetCellViewModel: ObservableObject{
@Environment(\.dataStore) private var dataStore
@Published var image : Image?
var indexAsset : IndexAsset?
var geoSize : CGSize
init(indexAsset: IndexAsset? = nil, geoSize:CGSize) {
self.indexAsset = indexAsset
self.geoSize = geoSize
self.requestImage(targetSize: CGSize(width: geoSize.width/4, height: geoSize.width/4))
}
func setIndexAsset(_ indexAsset:IndexAsset, targetSize: CGSize) {
self.indexAsset = indexAsset
self.requestImage(targetSize: targetSize)
}
func requestImage(targetSize: CGSize? = nil) {
if (self.indexAsset != nil) {
dataStore.fetchImageForLocalIdentifier(
id: indexAsset!.localIdentifier!,
targetSize: targetSize,
completionHandler: { image in
withAnimation(Animation.easeInOut (duration:0.15)) {
self.image = image
}
}
)
}
}
}
some of DataStore.swift
public class DataStore : ObservableObject {
static let shared = DataStore()
let persistenceController = PersistenceController.shared
@ObservedObject var assetFetcher = AssetFetcher()
let dateFormatter = DateFormatter()
var imageManager = PHCachingImageManager()
let id = UUID().uuidString
init() {
print(" init dataStore: \(self.id)")
dateFormatter.dateFormat = "yyyy-MM-dd"
assetFetcher.iterateResults{ asset in
do {
try self.registerAsset(
localIdentifier: asset.localIdentifier,
creationDate: asset.creationDate!,
isFavorite: asset.isFavorite
)
} catch {
print("Error registering asset \(asset)")
}
}
}
func registerAsset(localIdentifier:String, creationDate:Date, isFavorite:Bool) throws {
let alreadyExists = indexAssetEntityWithLocalIdentifier(localIdentifier)
if alreadyExists != nil {
// print(" Asset already registered: \(localIdentifier)")
// print(alreadyExists![0])
return
}
let iae = IndexAssetEntity(context: self.viewContext)
iae.localIdentifier = localIdentifier
iae.creationDate = creationDate
iae.creationDateKey = dateFormatter.string(from: creationDate)
iae.isFavorite = isFavorite
iae.isSelected = false
iae.isTrashed = false
self.viewContext.insert(iae)
try self.viewContext.save()
print(" Registered asset: \(localIdentifier)")
}
And AssetFetcher.swift
class AssetFetcher:NSObject, PHPhotoLibraryChangeObserver, ObservableObject {
@Published var fetchResults : PHFetchResult<PHAsset>? = nil
let id = UUID().uuidString
override init() {
super.init()
print(" init assetfetcher: \(id)")
self.startFetchingAllPhotos()
}
deinit {
PHPhotoLibrary.shared().unregisterChangeObserver(self)
}
func startFetchingAllPhotos() {
getPermissionIfNecessary(completionHandler: {result in
print(result)
})
let fetchOptions = PHFetchOptions()
var datecomponents = DateComponents()
datecomponents.month = -3
//TODO: request assets dynamically
let threeMonthsAgo = Calendar.current.date(byAdding: datecomponents, to:Date())
fetchOptions.predicate = NSPredicate(format: "creationDate > %@ AND creationDate < %@", threeMonthsAgo! as NSDate, Date() as NSDate)
fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
fetchOptions.wantsIncrementalChangeDetails = true
// fetchOptions.fetchLimit = 1000
let results = PHAsset.fetchAssets(with: .image, options: fetchOptions)
PHPhotoLibrary.shared().register(self)
print(" \(PHPhotoLibrary.shared())")
self.fetchResults = results
}
func iterateResults(_ callback:(_ asset: PHAsset) -> Void) {
print("iterateResults")
guard let unwrapped = self.fetchResults else {
return
}
for i in 0..<unwrapped.count {
callback(unwrapped.object(at: i))
}
}
func photoLibraryDidChange(_ changeInstance: PHChange) {
print(" photoLibraryDidChange")
DispatchQueue.main.async {
if let changeResults = changeInstance.changeDetails(for: self.fetchResults!) {
self.fetchResults = changeResults.fetchResultAfterChanges
// self.dataStore.photoLibraryDidChange(changeInstance)
// self.updateImages()
self.objectWillChange.send()
}
}
}
}
