Good afternoon,
I have been stuck on this problem for months. I am trying to use firebase storage to save image files that a user uploaded. The program should then be able to update the queue and show the image in a horizontal table view. Kinda like netflix where its titles of movies/shows but mine would just be pictures. After trying to figure this out, this is what I came up with. Here is to receive the images
class ImageRecieve : ObservableObject {
#Published var songImageArrayURL = [URL]()
#Published var data : Data?
#Published var songImage : NSImage?
#Published var AlbumCoverArray = [NSImage]()
func GetURLS(){
//we want to get the download urls
bfRef.listAll { (result, error) in
if let error = error{ //if theres an error, print it
print(error.localizedDescription)
}
let prefixes = result.prefixes
//loop to search each song prefix
for i in prefixes.indices{
//get the song of each prefix
prefixes[i].listAll { (result, error) in
if let error = error {
print(error.localizedDescription)
}
else {
let items = result.items
//if anything contains ".mp3" dont add it to array.
for j in items.indices{
if(!items[j].name.contains("mp3")){
SongImage.append(items[j])
self.download(SongImage: items[j])
}
}
}
}
}
}
}
func download(SongImage:StorageReference){
//get download url
DispatchQueue.main.async {
SongImage.downloadURL { (url, error) in
if let error = error { //if there is an error print it
print(error.localizedDescription)
}
else {
if(url != nil){
self.songImage = NSImage(byReferencing: url!)
self.AlbumCoverArray.append(self.songImage!)
}
}
}
}
}
func load(){
if(self.songImageArrayURL.isEmpty){
GetURLS()
}
print(self.songImageArrayURL)
for i in self.songImageArrayURL.indices{
print(self.songImageArrayURL[i])
DispatchQueue.global().async{
if let data = try? Data(contentsOf: self.songImageArrayURL[i]){
if let image = NSImage(data:data){
DispatchQueue.main.async {
self.songImage = image
}
}
}
}
}
}
func cancel(){
}
}
here is to load the images :
struct LoadImages<Placeholder: View>: View {
#ObservedObject var loader : ImageRecieve
private var placeholder : Placeholder?
init(placeholder: Placeholder? = nil) {
loader = ImageRecieve()
self.placeholder = placeholder
}
var body: some View {
image
.onAppear(perform: loader.GetURLS)
.onDisappear(perform: loader.cancel)
}
private var image: some View{
ForEach(loader.AlbumCoverArray.indices,id:\.self){
i in
Group{
if(self.loader.songImage != nil){
Image(nsImage:self.loader.AlbumCoverArray[i]).resizable().frame(width:50, height:50)
}
else{
self.placeholder
}
}
}
}
}
the problem I've been stuck on is that the photos are only downloading one at a time and not listing one by one. For example, they show one image and then switch to the next. I would like an array of images. So that the images get added to the list. I've tried using an image array but it doesnt work.
photos are only downloading one at a time and not listing one by one.
in all languages an array/list is processed sequentially, you might want to use multi-Threading for parallelism. use a queue and assign few threads which download image, after each download pop the element from queue.
all the child threads append/push the data to the main thread. in that manner you will be able to display images as they load.
PS:i am != swiftie but seeing your programming i sense turmoil. try improving your code grammar and avoid too many functions and spaces.
I have a problem with some code. I have a function called attachments. It calls on a DatabaseManager to a specific function getttachmentdata. This calls on coredata to see if a user has uploaded an image and call on it. If it has it I have another part of the code where the user clicks on a button and it shows that image.
The problem is that when the data is blank or there is nothing uploaded I wanted the button to be disabled. This might be a simple fix but I am not quite sure actually.
let attachments = DataBaseManager().getAttachmentData()
if attachments.isEmpty {
btnProofOfDelivery.isHidden = true
btnProofOfDelivery.isEnabled = false
}
I wrote the code above, however, when I tried running my program it still displayed the button that I wanted to disappear. Running without the if statement makes the button disappear.
code for getattachments
func getAttachmentData()-> Array<Data>{
var data1 = [Data]()
let context = CoreData.sharedCoreData.managedObjectContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Attachments")
do {
let result = try context.fetch(request)
print(result)
for data in result as! [NSManagedObject] {
print(data.value(forKey: "attachment") as! Data)
data1.append(data.value(forKey: "attachment") as! Data)
}
if data1.count == 0 {
return [Data()]
}else{
return data1
}
} catch {
return [Data()]
}
}
Below is your bug, if the fetch doesn't return anything you return a new Data object
if data1.count == 0 {
return [Data()]
}
You of course meant to write
if data1.count == 0 {
return [Data]()
}
and some issue in catch
or you can just remove all of that since data1 is properly initialised so you can just return it either way so the code after the for {} loop can then be reduced to
return data1
} catch {
print(error)
}
}
I am encoutering a strange issue:
I am using a backgroundFetch to fetch the data from Core Data.
func fetchDataFromCoreData(completion:#escaping()->Void)
{
let appdel = UIApplication.shared.delegate as! AppDelegate
let context = appdel.persistentContainer.viewContext
appdel.persistentContainer.performBackgroundTask { (context) in
let fetchReq = NSFetchRequest<NSFetchRequestResult>(entityName: "FreeApps")
do
{
let data = try context.fetch(fetchReq) as? [NSManagedObject]
self.resultData = data
print(self.resultData ?? "data is empty")
DispatchQueue.main.async{
completion()
}
}
catch
{
print("fetch error")
}
}
}
Now in my view Controller, in my table cell:
let myDict = itunesViewModelObj.resultData?[indexPath.row] as? NSManagedObject
print(myDict?.value(forKey: "name") as? String ?? "no name")myDict shows as fault but valefor key comes nil
Now if I comment the performBackgroundTask line data comes properly.
Please help as what can be the issue with backgroundTask.
Any suggestions will be highly appreciated!
Thanks in advance!
The PersistentContainer operates on the main queue. As the name of the property implies, this managed object context is designed to be used in combination with the application's user interface. Maybe you need to dispatch back to the main queue to interact with UIApplicationDelegate and PersistentContainer.
PerformBackgroundTask is generally used for updates to core data. If you are doing fetches you should use the main viewContext.
Maybe using...
DispatchQueue.main.async {
// your code
}
I'm trying to download images from my firebase database and load them into collectionviewcells. The images download, however I am having trouble having them all download and load asynchronously.
Currently when I run my code the last image downloaded loads. However, if I update my database the collection view updates and the new last user profile image also loads in but the remainder are missing.
I'd prefer to not use a 3rd party library so any resources or suggestions would be greatly appreciated.
Here's the code that handles the downloading:
func loadImageUsingCacheWithUrlString(_ urlString: String) {
self.image = nil
// checks cache
if let cachedImage = imageCache.object(forKey: urlString as NSString) as? UIImage {
self.image = cachedImage
return
}
//download
let url = URL(string: urlString)
URLSession.shared.dataTask(with: url!, completionHandler: { (data, response, error) in
//error handling
if let error = error {
print(error)
return
}
DispatchQueue.main.async(execute: {
if let downloadedImage = UIImage(data: data!) {
imageCache.setObject(downloadedImage, forKey: urlString as NSString)
self.image = downloadedImage
}
})
}).resume()
}
I believe the solution lies somewhere in reloading the collectionview I just don't know where exactly to do it.
Any suggestions?
EDIT:
Here is where the function is being called; my cellForItem at indexpath
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: userResultCellId, for: indexPath) as! FriendCell
let user = users[indexPath.row]
cell.nameLabel.text = user.name
if let profileImageUrl = user.profileImageUrl {
cell.profileImage.loadImageUsingCacheWithUrlString(profileImageUrl)
}
return cell
}
The only other thing that I believe could possibly affect the images loading is this function I use to download the user data, which is called in viewDidLoad, however all the other data downloads correctly.
func fetchUser(){
Database.database().reference().child("users").observe(.childAdded, with: {(snapshot) in
if let dictionary = snapshot.value as? [String: AnyObject] {
let user = User()
user.setValuesForKeys(dictionary)
self.users.append(user)
print(self.users.count)
DispatchQueue.main.async(execute: {
self.collectionView?.reloadData()
})
}
}, withCancel: nil)
}
Current Behavior:
As for the current behavior the last cell is the only cell that displays the downloaded profile image; if there are 5 cells, the 5th is the only one that displays a profile image. Also when I update the database, ie register a new user into it, the collectionview updates and displays the newly registered user correctly with their profile image in addition to the old last cell that downloaded it's image properly. The rest however, remain without profile images.
I know you found your problem and it was unrelated to the above code, yet I still have an observation. Specifically, your asynchronous requests will carry on, even if the cell (and therefore the image view) have been subsequently reused for another index path. This results in two problems:
If you quickly scroll to the 100th row, you are going to have to wait for the images for the first 99 rows to be retrieved before you see the images for the visible cells. This can result in really long delays before images start popping in.
If that cell for the 100th row was reused several times (e.g. for row 0, for row 9, for row 18, etc.), you may see the image appear to flicker from one image to the next until you get to the image retrieval for the 100th row.
Now, you might not immediately notice either of these are problems because they will only manifest themselves when the image retrieval has a hard time keeping up with the user's scrolling (the combination of slow network and fast scrolling). As an aside, you should always test your app using the network link conditioner, which can simulate poor connections, which makes it easier to manifest these bugs.
Anyway, the solution is to keep track of (a) the current URLSessionTask associated with the last request; and (b) the current URL being requested. You can then (a) when starting a new request, make sure to cancel any prior request; and (b) when updating the image view, make sure the URL associated with the image matches what the current URL is.
The trick, though, is when writing an extension, you cannot just add new stored properties. So you have to use the associated object API to associate these two new stored values with the UIImageView object. I personally wrap this associated value API with a computed property, so that the code for retrieving the images does not get too buried with this sort of stuff. Anyway, that yields:
extension UIImageView {
private static var taskKey = 0
private static var urlKey = 0
private var currentTask: URLSessionTask? {
get { objc_getAssociatedObject(self, &UIImageView.taskKey) as? URLSessionTask }
set { objc_setAssociatedObject(self, &UIImageView.taskKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC) }
}
private var currentURL: URL? {
get { objc_getAssociatedObject(self, &UIImageView.urlKey) as? URL }
set { objc_setAssociatedObject(self, &UIImageView.urlKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC) }
}
func loadImageAsync(with urlString: String?, placeholder: UIImage? = nil) {
// cancel prior task, if any
weak var oldTask = currentTask
currentTask = nil
oldTask?.cancel()
// reset image view’s image
self.image = placeholder
// allow supplying of `nil` to remove old image and then return immediately
guard let urlString = urlString else { return }
// check cache
if let cachedImage = ImageCache.shared.image(forKey: urlString) {
self.image = cachedImage
return
}
// download
let url = URL(string: urlString)!
currentURL = url
let task = URLSession.shared.dataTask(with: url) { [weak self] data, response, error in
self?.currentTask = nil
// error handling
if let error = error {
// don't bother reporting cancelation errors
if (error as? URLError)?.code == .cancelled {
return
}
print(error)
return
}
guard let data = data, let downloadedImage = UIImage(data: data) else {
print("unable to extract image")
return
}
ImageCache.shared.save(image: downloadedImage, forKey: urlString)
if url == self?.currentURL {
DispatchQueue.main.async {
self?.image = downloadedImage
}
}
}
// save and start new task
currentTask = task
task.resume()
}
}
Also, note that you were referencing some imageCache variable (a global?). I would suggest an image cache singleton, which, in addition to offering the basic caching mechanism, also observes memory warnings and purges itself in memory pressure situations:
class ImageCache {
private let cache = NSCache<NSString, UIImage>()
private var observer: NSObjectProtocol?
static let shared = ImageCache()
private init() {
// make sure to purge cache on memory pressure
observer = NotificationCenter.default.addObserver(
forName: UIApplication.didReceiveMemoryWarningNotification,
object: nil,
queue: nil
) { [weak self] notification in
self?.cache.removeAllObjects()
}
}
deinit {
NotificationCenter.default.removeObserver(observer!)
}
func image(forKey key: String) -> UIImage? {
return cache.object(forKey: key as NSString)
}
func save(image: UIImage, forKey key: String) {
cache.setObject(image, forKey: key as NSString)
}
}
A bigger, more architectural, observation: One really should decouple the image retrieval from the image view. Imagine you have a table where you have a dozen cells using the same image. Do you really want to retrieve the same image a dozen times just because the second image view scrolled into view before the first one finished its retrieval? No.
Also, what if you wanted to retrieve the image outside of the context of an image view? Perhaps a button? Or perhaps for some other reason, such as to download images to store in the user’s photos library. There are tons of possible image interactions above and beyond image views.
Bottom line, fetching images is not a method of an image view, but rather a generalized mechanism of which an image view would like to avail itself. An asynchronous image retrieval/caching mechanism should generally be incorporated in a separate “image manager” object. It can then detect redundant requests and be used from contexts other than an image view.
As you can see, the asynchronous retrieval and caching is starting to get a little more complicated, and this is why we generally advise considering established asynchronous image retrieval mechanisms like AlamofireImage or Kingfisher or SDWebImage. These guys have spent a lot of time tackling the above issues, and others, and are reasonably robust. But if you are going to “roll your own,” I would suggest something like the above at a bare minimum.
I have a button to save picture data in core data but when I push it, it is freezing because size of the data is big. I did try to use dispatch_async but it didn’t work. How do I create the icon/indicator showing that it is loading/bookmarking rather than just freezing?
#IBAction func save() {
let content = self.foodMenu?["content"].string
let urlString = self.foodMenu?["thumbnail_images"]["full"]["url"]
let urlshare = NSURL(string: urlString!.stringValue)
let imageData = NSData(contentsOfURL: urlshare!)
let images = UIImage(data: imageData!)
dispatch_async(dispatch_get_main_queue(), {
if let managedObjectContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext {
self.foodClass = NSEntityDescription.insertNewObjectForEntityForName("Foods",
inManagedObjectContext: managedObjectContext) as! Foods
self.foodClass.content = content
self.foodClass.image = UIImageJPEGRepresentation(images, 1)
var e: NSError?
if managedObjectContext.save(&e) != true {
println("insert error: \(e!.localizedDescription)")
return
}
}
First, it is unlikely it is the save that is slow. I would suspect that your creation of the JPEG representation is the slow part.
Second, you are wanting to hide a problem by putting up a spinner. That really is bad for the user experience. Far better to do the following (yes it is more code);
Move your image creation and saving to a background queue.
Restructure your Core Data stack so that your saves to disk are on a private queue.
This involves using a background queue and multiple contexts in Core Data but getting this data processing off the User Interface thread is the right answer.