Considering I'm using PFImageViews, with caching enabled, I would like to know if there's a way to determine whether an image has already been downloaded or not.
All in all, I want to say:
if imageAlreadyDownloaded {
...
}
else {
...
}
Is it possible?
So, I finally found the solution to my own problem! Every PFFile, has a boolean property called "isDataAvailable".
With a bit of code we can have the following solution:
let imageFile = file as? PFFile
if imageFile.isDataAvailable {
...
}
else {
...
}
And done! ;-)
I think you will have to roll your own solution using the PFImageView and the loadInBackground method that has a completion handler.
Something like:
// Instance property on your UIViewController
private var imageAlreadyDownloaded = false
// Somewhere else in your UIViewController...
imageView.loadInBackground() {
[unowned self] (image, error) in
guard error == nil else {
return
}
self.imageAlreadyDownloaded = true
}
Related
I want get folders and images from Firebase storage. On this code work all except one moment. I cant append array self.collectionImages in array self.collectionImagesArray. I don't have error but array self.collectionImagesArray is empty
class CollectionViewModel: ObservableObject {
#Published var collectionImagesArray: [[String]] = [[]]
#Published var collectionImages = [""]
init() {
var db = Firestore.firestore()
let storageRef = Storage.storage().reference().child("img")
storageRef.listAll { (result, error) in
if error != nil {
print((error?.localizedDescription)!)
}
for prefixName in result.prefixes {
let storageLocation = String(describing: prefixName)
let storageRefImg = Storage.storage().reference(forURL: storageLocation)
storageRefImg.listAll { (result, error) in
if error != nil {
print((error?.localizedDescription)!)
}
for item in result.items {
// List storage reference
let storageLocation = String(describing: item)
let gsReference = Storage.storage().reference(forURL: storageLocation)
// Fetch the download URL
gsReference.downloadURL { url, error in
if let error = error {
// Handle any errors
print(error)
} else {
// Get the download URL for each item storage location
let img = "\(url?.absoluteString ?? "placeholder")"
self.collectionImages.append(img)
print("\(self.collectionImages)")
}
}
}
self.collectionImagesArray.append(self.collectionImages)
print("\(self.collectionImagesArray)")
}
//
self.collectionImagesArray.append(self.collectionImages)
}
}
}
If i put self.collectionImagesArray.append(self.collectionImages) in closure its works but its not what i want
The problem is caused by the fact that calling downloadURL is an asynchronous operation, since it requires a call to the server. While that call is happening, your main code continues so that the user can continue to use the app. Then when the server returns a value, your closure/completion handler is invoked, which adds the URL to the array. So your print("\(self.collectionImagesArray)") happens before the self.collectionImages.append(img) has ever been called.
You can also see this in the order that the print statements occur in your output. You'll see the full, empty array first, and only then see the print("\(self.collectionImages)") outputs.
The solution for this problem is always the same: you need to make sure you only use the array after all the URLs have been added to it. There are many ways to do this, but a simple one is to check whether your array of URLs is the same length as result.items inside the callback:
...
self.collectionImages.append(img)
if self.collectionImages.count == result.items.count {
self.collectionImagesArray.append(self.collectionImages)
print("\(self.collectionImagesArray)")
}
Also see:
How to wait till download from Firebase Storage is completed before executing a completion swift
Closure returning data before async work is done
Return image from asynchronous call
SwiftUI: View does not update after image changed asynchronous
I am using Parse and PFUser in a Swift iOS app, and find myself in a case where PFUser.current() does not do exactly what I want, due to synchronisation issues.
For that reason I am trying to use: PFUser.getCurrentUserInBackground().
I got started with the code below, inspired from what can be found here: https://github.com/BoltsFramework/Bolts-ObjC.
But this document probably being a bit outdated, it does not quite work.
let userCheckTask = PFUser.getCurrentUserInBackground()
userCheckTask.continueWith {
(task: BFTask!) -> BFTask<AnyObject> in
if task.isCancelled() { // Error-1.
// the save was cancelled.
} else if task.error != nil {
// the save failed.
} else {
// the object was saved successfully.
var object = task.result() as PFObject // Error-2.
}
}
The compiler gives me two errors, this one on the line marked "Error-1"
Cannot invoke 'isCancelled' with no arguments
And this other one on the line marked "Error-2"
Expression type 'PFUser?' is ambiguous without more context
I have no idea what kind of argument 'isCancelled' is expecting.
Does anyone know how to fix those?
let userCheckTask = PFUser.getCurrentUserInBackground()
userCheckTask.continueWith {
(task: BFTask) -> BFTask<AnyObject> in
if let e = task.error {
return BFTask(error: e)
} else {
return BFTask(result: task.result)
}
}
I am using File manger to save a simple JSON file. The issue is I want to do this asynchronously and on the background thread. So far I am having issues getting this accomplished. I am adding a code sample below and would welcome some help! Thanks!
init(apiService: apiService) {
self.updateAction = Action(apiService.revision)
self.updateAction.values.observeValues { [weak self] revisionDataContainer in
guard let data = revisionDataContainer.data, let this = self else {
return
}
do {
try this.save(data: data, to: this.currentRevisionUrl)
this.currentRevision.value = try this.parse(data: data) as Revision
} catch let error {
debugPrint(error.localizedDescription)
}
}
do {
if FileManager.default.fileExists(atPath: self.currentRevisionUrl.path) {
self.currentRevision.value = try self.load(from: self.currentRevisionUrl) as Revision
} else {
self.currentRevision.value = try self.load(from: self.seedRevisionUrl) as Revision
}
} catch let error {
debugPrint(error.localizedDescription)
}
}
If you want to run this code in background thread, then you need to create a new instance of FileManager instead of using default.
This method always represents the same file manager object. If you
plan to use a delegate with the file manager to receive notifications
about the completion of file-based operations, you should create a new
instance of FileManager (using the init method) rather than using the
shared object.
https://developer.apple.com/documentation/foundation/filemanager/1409234-default
I'm trying to generate an array of PFObjects called 'areaList'. I've been researching this quite a bit and understand that I could benefit from using a completion handler to handle the asynchronous nature of the loaded results. My ask, specifically, is to get some guidance on what I'm doing wrong as well as potential tips on how to achieve the result "better".
Here is my query function with completion handler:
func loadAreasNew(completion: (result: Bool) -> ()) -> [Area] {
var areaList = self.areaList
let areaQuery = PFQuery(className: "Area")
areaQuery.findObjectsInBackgroundWithBlock {
(areas: [PFObject]?, error: NSError?) -> Void in
if error == nil {
for area in areas! {
let areaToAdd = area as! Area
areaList.append(areaToAdd)
// print(areaList) // this prints the list each time
// print(areaToAdd) // this prints the converted Area in the iteration
// print(area) // this prints the PFObject in the iteration
if areaList.count == areas!.count {
completion(result: true)
} else {
completion(result: false)
}
}
} else {
print("There was an error")
}
}
return areaList
}
Here is how I'm attempting to call it in viewDidLoad:
loadAreasNew { (result) -> () in
if (result == true) {
print(self.areaList)
} else {
print("Didn't Work")
}
}
I assigned this variable before viewDidLoad:
var areaList = [Area]()
In the console, I get the following:
Didn't Work
Didn't Work
Didn't Work
Didn't Work
[]
Representing the 5 items that I know are there in Parse...
This is an interesting question. First off, PFQuery basically has a built in completion handler, which is quiet nice! As you probably know, all of the code within the areaQuery.findObjectsInBackgroundWithBlock {...} triggers AFTER the server response. A completion most often serves the purpose of creating a block, with the ability of asynchronously returning data and errors.
Best practice would (IMO) to just call the code that you want to use with the results from your PFQuery right after your area appending loop (which I'm gonna take out because I'm picky like that), like so:
func loadAreasNew() {
var areaList = self.areaList
let areaQuery = PFQuery(className: "Area")
areaQuery.findObjectsInBackgroundWithBlock {
(areas: [PFObject]?, error: NSError?) -> Void in
if error == nil {
let areasFormatted = areas! As [Areas]
areasList += areasFormatted
//Something like this
self.codeINeedAreasFor(areasList)
}
} else {
print(error)
}
}
}
HOWEVER! If you really feel the need to use some completion handlers, check out this other answer for more info on how to use them. But keep in mind all tools have a time and a place...
There are a few issues here.
Your completion handler doesn't require you to define the name for your completion handler's parameters, so you could easily use completion: (Bool) -> ()
Further in your function, you're returning areaList. This should be put through the completion handler like this onComplete(areaList) and change your completion handler parameter to expect your area list.
Then, when you call your function, it could look more like this :
loadAreasNew { result in
if (result == true) {
print(self.areaList)
} else {
print("Didn't Work")
}
}
Here is my concern:
1) Don't pass in a local variable and make the function return it, it's meaningless and danger.
You may want to initiate an empty array and make your fetch, then "return" it.
2) The fetch request is processed in background, you will have no idea when it will have finished. If you return the array immediately it will always be an empty array.
Put the "return" in your completion too.
3) Parse already has a distance checking method, you don't have to do it manually. aPARSEQUERRY.where(key:,nearGeoPoint:,inKilometers:)
I will rewrite the function as:
func loadNewAreas(completion:([Area],err?)->()){
let areaQuery = PFQuery(className: "Area")
areaQuery.where("location",nearGeoPoint:MYCURRENTLOCATION,inKilometers:50)
areaQuery.findObjectInBackgroundWithBlock(){objects,err
if objects.count == 0
{
completion([],err)
}
let areas = Area.areasFromPFObjects(objects)
completion(areas,err)
}
}
I have an NSData object stored in my core data. I want to be able to check if it exist or not using an if statement. I can't seem to work it out. I have the variable set up as:
var coreImage : NSData?
and I have tried using:
if (coreImage != nil) {
println("Use core image")
}else {
println("Do something else")
}
I know I have NSData stored in core data but it never runs the if statement as I want it too so I must be doing something wrong?
Can anyone help?
Thanks.
Check if NSData's length is > 0, that's it.
Example:
if (coreImage.length > 0) {
//we're cool
}
I am newer to Swift than you, but I think you need to do some special work to access and utilize items from Core Data. Try something like this:
let fetchRequest = NSFetchRequest(entityName: "coreImage")
if let fetchResults = managedObjectContext!.executeFetchRequest(fetchRequest, error: nil) as? [NSData] {
println("Use core image")
} else {
println("Do something else")
}