I am using NSFetchedResultsController with UITableView, and my core-data class have field #NSManaged public var avatar_data: Data? , and image data is getting download when cell is visible(lazy loading). when download is completed and data is set into avatar_data field. it's trigger
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?){
}
I Wish to ignore any changes for avatar_data field. notification should not trigger for particular field i.e avatar_data field.
problem is it's create cycle of reload tableview. i don't have download status for image. i simply want to ignore data change notification for this field.
extension UIImageView{
func downloadImageFrom(link:String, contentMode: UIViewContentMode, forContact:ContactDB, forCell:UserListTableViewCell) {
URLSession.shared.dataTask( with: NSURL(string:link)! as URL, completionHandler: {
(data, response, error) -> Void in
DispatchQueue.main.async() {
self.contentMode = contentMode
if let data = data {
self.image = UIImage(data: data)
forContact.avatar_thumb_data = data
//should not call didchange content of fetechresultcontroller
forContact.setPrimitiveValue(data, forKey: "avatar_thumb_data")
CoreDataInterface.sharedInstance.saveContext()
forCell.imageUserProfile?.backgroundColor = UIColor.clear
forCell.labelUserImage.text = ""
}
}
}).resume()
}
}
SetPrimitiveValue is applied after image download completed.
Related
I'm currently implementing an App which has a collectionView. The cells in the collection view are filled via an API-request. The requests are to the same API but with different locations. So for example for the first cell I'm calling: "google.de/GamesInItaly" and for the second cell: "google/GamesInGermany". While I'm scrolling down the collectionView the appearing cells should also make an API-request that has different countries.
The Problem I'm facing is, that I don't know how to handle the different API calls.
I managed to make one API-request and fill every cell with the same data, but I want different data for every cell.
My code looks like this:
CollectionView:
Call with from collectionView:
func fetchMatch() {
ApiService.sharedInstance.fetchGames(from: contentURL, completion: { (content: [[contentModel]]) in
self.content = content
self.collectionView.reloadData()
})
}
API-Services:
Set the Url:
func fetchGames(from url: String, completion: #escaping ([contentModel]) -> ()) {
fetchFeedForUrlString(urlString: "\(BaseUrl)/getgames/\(url)", completion: completion)
}
Fetch function:
func fetchFeedForUrlString<T: Decodable>(urlString: String, completion: #escaping (T) -> ())
{
let url = URL(string: urlString)
let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in
guard let data = data else {
return
}
do {
let json = try JSONDecoder().decode(T.self, from: data)
DispatchQueue.main.async {
completion(json)
}
} catch let jsonError {
print(jsonError)
}
}
task.resume()
}
I think what I could do is make many of these fetchGames functions, but I think that would be a bad practice.
I've also read about DispatchGroup but I'm not really sure how I can implement these into my program.
Does somebody know how I can handle multiple API-calls in a good practice?
I am wondering if there is any way to keep reloading a tableView as items are being downloaded.
There are images and info associated with those images. When the user first opens the app, the app begins downloading images and data using HTTP. The user can only see downloaded items in the tableView as they're being downloaded if he/she keeps leaving the viewController and coming back to it.
I have tried doing something like this:
while downloading {
tableView.reloadData()
}
, however, this uses too much memory and it crashes the app.
How can I asynchronously populate a tableView with images and data as they are being downloaded while still remaining in the tableViewController?
P.S. If you're interested in which libraries or APIs I'm using, I use Alamofire to download and Realm for data persistence.
The correct and usual way to do this is reload data into table, than delegate the single cell to load asyncronously the image from a link.
In swift, you can extend UIImage
extension UIImageView {
func imageFromUrl(urlString: String) {
if let url = NSURL(string: urlString) {
let request = NSURLRequest(URL: url)
NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) {
(response: NSURLResponse?, data: NSData?, error: NSError?) -> Void in
if let imageData = data as NSData? {
self.image = UIImage(data: imageData)
}
}
}
}
}
And in your CellForRowAtIndexPath load the image from link using something like this
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
...
cell.image.imageFromUrl(dataArray[indexPath.row].imageUrl)
return cell
}
I have a UITable-View with a List of Users and their Profile Pictures.
I am loading the pictures (http://api/pictures/{userid}) one by one for each player asynchronous:
func loadImageAsync(imageUrl: URL, completionHandler handler: #escaping (_ success: Bool, _ image: UIImage?) -> Void){
DispatchQueue.global(qos: .userInitiated).async { () -> Void in
if let imgData = try? Data(contentsOf: imageUrl), let img = UIImage(data: imgData) {
DispatchQueue.main.async(execute: { () -> Void in
handler(true, img)
})
} else {
handler(false, nil)
}
}
In the completion handler in the cellForRowAt-Index-Fuction, I am setting the pictures.
loadImageAsync(imageUrl: imageUrl!, label: ip) { (success, image, backlabel) -> Void in
if(success){
cell.profilePictureView.image = image
}
}
However, when I scroll very fast, some pictures get loaded in the wrong cells.
To prevent reuse-issues, I am "resetting" the image view after every reuse:
override func prepareForReuse() {
profilePictureView.image = UIImage(named: "defaultProfilePicture")
}
But why are still some images loaded false when scrolling fastly?
hmmm, this is what I thought too.
__Update:
So, I extended the function with a Label Parameter (type Any), that is returned back as it was put in the function. I tried to compare the parameter (is used the indexpath) with the current indexpath. Actually, this should work - shouldn't it?!
loadImageAsync(imageUrl: imageUrl!, label: ip) { (success, image, backlabel) -> Void in
cell.loader.stopAnimating()
if (backlabel as! IndexPath == indexPath) {
//set image...
But however, it doesn't show any effect. Do you know why or have any other solutions to fix this?
The issue is that if you scroll fast, the download may take long enough that by the time it's complete, the cell in question has scrolled off the screen and been recycled for a different indexPath in your data model.
The trick is to ask the table view for the cell at that indexPath in the completion block and only install the image if you get a cell back:
loadImageAsync(imageUrl: imageUrl!, label: ip, for indexPath: IndexPath) { (success, image, backlabel) -> Void in
if(success){
let targetCell = tableview.cell(for: indexPath)
targetCell.profilePictureView.image = image
}
}
EDIT:
Redefine your loadImageAsync function like this:
func loadImageAsync(imageUrl: URL,
indexPath: IndexPath,
completionHandler handler: #escaping (_ success: Bool,
_ image: UIImage?,
_ indexPath: IndexPath ) -> Void) { ... }
EDIT #2
And by the way, you should really save your images to disk and load them from there rather than loading from the internet each time. I suggest using a hash of the image URL as a filename.
Modify loadImageAsync as follows:
Check to see if the file already exists on disk. If so, load it and return it.
If the file does not exist, do the async load, and then save it to disk using the hash of the URL as a filename, before returning the in-memory image.
Because your completionHandler can be called after the cell has been reused for the next user, and possibly another image request for the cell has been fired. The order of events (reuse/completion) is not predictable, and in fact a later async request could complete before an earlier one.
I building message app with meteor-iOS, everything is going great but I'm trying to make a load more feature but I can't maintain/save the position of scroll view(When I scroll to top I want to load more items but keep the scroll view in the same position as before the insert)
My Code:
func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
if type == NSFetchedResultsChangeType.Insert {
self.blockOperations.append(
NSBlockOperation(block: { [weak self] in
if let this = self {
this.collectionView!.insertItemsAtIndexPaths([newIndexPath!])
}
})
)
}
else if type == NSFetchedResultsChangeType.Update {
self.blockOperations.append(
NSBlockOperation(block: { [weak self] in
if let this = self {
this.collectionView!.reloadItemsAtIndexPaths([indexPath!])
}
})
)
}
else if type == NSFetchedResultsChangeType.Move {
self.blockOperations.append(
NSBlockOperation(block: { [weak self] in
if let this = self {
this.collectionView!.moveItemAtIndexPath(indexPath!, toIndexPath: newIndexPath!)
}
})
)
}
else if type == NSFetchedResultsChangeType.Delete {
self.blockOperations.append(
NSBlockOperation(block: { [weak self] in
if let this = self {
this.collectionView!.deleteItemsAtIndexPaths([indexPath!])
}
})
)
}
}
self.collectionView!.performBatchUpdates({ () -> Void in
for operation: NSBlockOperation in self.blockOperations {
operation.start()
}
}, completion: { (finished) -> Void in
self.blockOperations.removeAll(keepCapacity: false)
})
I'm using core data and meteor-ios. those anyone know what I can do? I also tried how to set UITableView's scroll position to previous location when click "load earlier items" button any many other without success :(
Thank you very much!!
Yep, I made if statement between range 20-50 to contentOffset.y. If it between those values so call loadMore() once.
Make bool value to save isLoadFinish and wait until the cell update. If you wouldn't do it the loadMore() will call multiple time.
For UX experience you have to save the old contentOffset.y before calling loadMore() and reset it after the load.
I will need to improve it a lot, simple hack for now.
Good luck.
I have a header view for every UITableViewCell. In this header view, I load a picture of an individual via an asynchronous function in the Facebook API. However, because the function is asynchronous, I believe the function is called multiple times over and over again, causing the image to flicker constantly. I would imagine a fix to this issue would be to load the images in viewDidLoad in an array first, then display the array contents in the header view of the UITableViewCell. However, I am having trouble implementing this because of the asynchronous nature of the function: I can't seem to grab every photo, and then continue on with my program. Here is my attempt:
//Function to get a user's profile picture
func getProfilePicture(completion: (result: Bool, image: UIImage?) -> Void){
// Get user profile pic
let url = NSURL(string: "https://graph.facebook.com/1234567890/picture?type=large")
let urlRequest = NSURLRequest(URL: url!)
//Asynchronous request to display image
NSURLConnection.sendAsynchronousRequest(urlRequest, queue: NSOperationQueue.mainQueue()) { (response:NSURLResponse!, data:NSData!, error:NSError!) -> Void in
if error != nil{
println("Error: \(error)")
}
// Display the image
let image = UIImage(data: data)
if(image != nil){
completion(result: true, image: image)
}
}
}
override func viewDidLoad() {
self.getProfilePicture { (result, image) -> Void in
if(result == true){
println("Loading Photo")
self.creatorImages.append(image!)
}
else{
println("False")
}
}
}
func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
//Show section header cell with image
var cellIdentifier = "SectionHeaderCell"
var headerView = tableView.dequeueReusableCellWithIdentifier(cellIdentifier) as! SectionHeaderCell
headerView.headerImage.image = self.creatorImages[section]
headerView.headerImage.clipsToBounds = true
headerView.headerImage.layer.cornerRadius = headerView.headerImage.frame.size.width / 2
return headerView
}
As seen by the program above, I the global array that I created called self.creatorImages which holds the array of images I grab from the Facebook API is always empty and I need to "wait" for all the pictures to populate the array before actually using it. I'm not sure how to accomplish this because I did try a completion handler in my getProfilePicture function but that didn't seem to help and that is one way I have learned to deal with asynchronous functions. Any other ideas? Thanks!
I had the same problem but mine was in Objective-C
Well, the structure is not that different, what i did was adding condition with:
headerView.headerImage.image
Here's an improved solution that i think suits your implementation..
since you placed self.getProfilePicture inside viewDidLoad it will only be called once section==0 will only contain an image,
the code below will request for addition image if self.creatorImages's index is out of range/bounds
func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
//Show section header cell with image
var cellIdentifier = "SectionHeaderCell"
var headerView = tableView.dequeueReusableCellWithIdentifier(cellIdentifier) as! SectionHeaderCell
if (section < self.creatorImages.count) // validate self.creatorImages index to prevent 'Array index out of range' error
{
if (headerView.headerImage.image == nil) // prevents the blinks
{
headerView.headerImage.image = self.creatorImages[section];
}
}
else // requests for additional image at section
{
// this will be called more than expected because of tableView.reloadData()
println("Loading Photo")
self.getProfilePicture { (result, image) -> Void in
if(result == true) {
//simply appending will do the work but i suggest something like:
if (self.creatorImages.count <= section)
{
self.creatorImages.append(image!)
tableView.reloadData()
println("self.creatorImages.count \(self.creatorImages.count)")
}
//that will prevent appending excessively to data source
}
else{
println("Error loading image")
}
}
}
headerView.headerImage.clipsToBounds = true
headerView.headerImage.layer.cornerRadius = headerView.headerImage.frame.size.width / 2
return headerView
}
You sure have different implementation from what i have in mind, but codes in edit history is not in vain, right?.. hahahaha.. ;)
Hope i've helped you.. Cheers!