I have created a CollectionView where displays the photos from the camera roll, just like the default photo app of iPhone (one cell per photo)
I need to implement a delete functionality, so I successfully created a delete action. The problem is when I am trying to reload the data of the collection view.
To give an example I want to mimic the default's photo app behavior on delete.
Below I have the code which crashes. It is executed after successfully delete action.
func removeFromCollectionView() {
let ip = self._collectionView.indexPathsForVisibleItems
self._itemsCount? -= 1
_collectionView.deleteItems(at: ip)
_collectionView.performBatchUpdates({
self._collectionView.reloadItems(at: ip)
}, completion: nil)
}
The error is:
This application is modifying the autolayout engine from a background thread after the engine was accessed from the main thread. This can lead to engine corruption and weird crashes.
Also, I have tried to wrap the code into
DispatchQueue.main.async { }
I tried to be explanatory let me know if you need more, does anyone has an idea? Thanks in advance.
EDIT:
I did the below changes based on comments. The code does not crash but does not delete the photo
func removeFromCollectionView() {
let ip = self._collectionView.indexPathsForVisibleItems
self._itemsCount? -= 1
_collectionView.performBatchUpdates({
self._collectionView.deleteItems(at: ip)
}, completion: { finished in
if finished {
print("finished")
self._collectionView.reloadData()
}
})
}
Related
WKInterfaceMap sometimes renders blank in a very simple app I am developing. The map appears completely empty (no grid of lines or anything similar). It looks as though the thread responsible for drawing the tiles gets blocked.
In order to reproduce the issue just add the code below to the extension delegate.
func applicationDidEnterBackground() {
let watchExtension = WKExtension.shared()
// Schedule the background refresh task.
watchExtension.scheduleBackgroundRefresh(withPreferredDate: Date().addingTimeInterval(15.0*60.0), userInfo: nil) { (error) in
// Check for errors.
if let error = error {
print("ExtensionDelegate: \(error.localizedDescription)")
return
}
print("ExtensionDelegate: Background Task scheduled successfuly")
}
}
Add a WKInterfaceMap to the main view and run once on the simulator. Close the app using the crown and stop it from XCode. Wait for at least 15 minutes and open the app again directly from the simulator.
The map renders then as in the image below.
I'm developing a photo editing extension for iOS, bundled in a container app that provides the same photo editing functionality.
In order to reuse code, I have a view controller class that adopts the required PHContentEditingController protocol, and I subclassed it for use both as the main interface of the app extension, and as the "working screen" of the container app.
On the editing extension, the controller's methods are called by the Photos app's editing session as described in Apple's documentation and various tutorials you can find around the web.
On the container app, on the other hand, I first obtain a PHAsset instance by means of the UIImagePickerController class, and directly start the editing session manually on my "work" view controller like this:
// 'work' is my view controller which adopts
// `PHContentEditingController`. 'workNavigation'
// embeds it.
let options = PHContentEditingInputRequestOptions()
options.canHandleAdjustmentData = { (adjustmentData) in
return work.canHandle(adjustmentData)
}
asset.requestContentEditingInput(with: options, completionHandler: { [weak self] (input, options) in
// (Called on the Main thread on iOS 10.0 and above)
guard let this = self else {
return
}
guard let editingInput = input else {
return
}
work.asset = asset
work.startContentEditing(with: editingInput, placeholderImage: editingInput.displaySizeImage!)
this.present(workNavigation, animated: true, completion: nil)
})
When the user finishes editing, the work view controller calls finishContentEditing(completionHandler: on itself to finish the session:
self.finishContentEditing(completionHandler: {(output) in
// nil output results in "Revert" prompt.
// non-nil output results in "Modify" prompt.
let library = PHPhotoLibrary.shared()
library.performChanges({
let request = PHAssetChangeRequest(for: self.asset)
request.contentEditingOutput = output
}, completionHandler: {(didSave, error) in
if let error = error {
// handle error...
} else if didSave {
// proceed after saving...
} else {
// proceed after cancellation...
}
})
})
Within the editing session, the user can 'clear' the previous edits passed as adjustment data, effectively reverting the image to its original state.
I've noticed that, if I finish the editing by calling the completion handler passed to finishContentEditing(completionHandler:) with nil as its argument (instead of a valid PHContentEditingOutput object), the Photos framework will prompt the user to "revert" the image instead of "modifying" it:
func finishContentEditing(completionHandler: #escaping (PHContentEditingOutput?) -> Void) {
guard let editingInput = self.editingInput, let inputURL = editingInput.fullSizeImageURL else {
return completionHandler(nil)
}
if editingInput.adjustmentData != nil && hasUnsavedEdits == false {
// We began with non-nil adjustment data but now have
// no outstanding edits - means REVERT:
return completionHandler(nil)
}
// (...proceed with writing output to url...)
However, this only works when running from the container app. If I try the same trick from the extension (i.e., load an image that contains previous edits, reset them, and tap 'Done') I get the dreaded "Unable to Save Changes" message...
What is the correct way to revert previous edits to an image from within a photo editing extension?
Months later, still no answer, so I begrudgingly adopted this workaround (which is still preferable to an error alert):
When the user taps "Done" from the Photos extension UI and the image has no edits applied to it (either because the user reset previous edits, or didn't apply any changes to a brand new image), perform the following actions from within finishContentEditing(completionHandler:):
Create adjustment data that amounts to no visible changes at all ("null effect") and archive it as Data.
Create a PHAdjustmentData instance with the "null effect" data from above, with the formatVersion and formatIdentifier properly set.
Create a PHContentEditingOutput instance from the editing input passed at the beginning of the session (as usual), and set the adjustment data created above.
Read the unmodified image from the inputURL property of the editing input, and write it unmodified to the url specified by the PHContentEditingOutput instance's renderedContentURL property.
Call the completionHandler block, passing the editing output instance (as normal).
The result: The image is saved in its original state (no effects applied), and no alerts or errors occur.
The drawback: The library asset remains in the 'edited' state (because we passed non-nil editing output and adjustment data, there was no other choice), so the next time the user tries to edit it from Photos.app, the red 'Revert' button will be present:
However, choosing 'revert' results in no visible changes to the image data (duh!), which can be confusing to the user.
—-
Update
I checked what the built-in “Markup” extension does:
...and it is consistent with my workaround above, so I guess this is the best that can be done.
I'm using this GitHub project's controller for displaying user's Photo Gallery inside of UICollectionView. Everything is okay there, but except one: If I run it for the first time, it asks me about permissions. I accept it, but after that I cannot get my images from the gallery. It displays nothing.
But when I close my app and run again it can get my photos from the gallery. So, this problem appears just on the first launch.
Can anyone help me, how can I solve it?
UPDATE
I suppose, that this observer works incorrect:
func photoLibraryDidChange(changeInstance: PHChange) {
let changeDetails = changeInstance.changeDetailsForFetchResult(images)
self.images = changeDetails!.fetchResultAfterChanges
dispatch_async(dispatch_get_main_queue()) {
// Loop through the visible cell indices
let indexPaths = self.imagesCollectionView.indexPathsForVisibleItems()
for indexPath in indexPaths as [NSIndexPath]! {
if changeDetails!.changedIndexes!.containsIndex(indexPath.item) {
let cell = self.imagesCollectionView?.cellForItemAtIndexPath(indexPath) as! ImagesCollectionViewCell
cell.imageAsset = changeDetails!.fetchResultAfterChanges[indexPath.item] as? PHAsset
}
}
}
}
So, I give permissions, but it doesn't show me my photos. For this I need to relaunch my app
If you want any code - I can share it. But I'm using the above github controller which I've attached above.
Since it works correctly when you relaunch the app it sounds like you are probably asking for permissions at the same time you are displaying the view controller/collection view. The problem is that the collection view doesn't know to reload once the user has selected to give your app access to their photos. In the PHPhotoLibrary.requestAuthorization call back you need to tell your view controller/collection view to reload once they have Authorized your app. Small example below:
PHPhotoLibrary.requestAuthorization { status in
switch status {
case .Authorized:
/* RELOAD COLLECTION VIEW HERE */
case .Restricted:
<#your code#>
case .Denied:
<#your code#>
default:
// place for .NotDetermined - in this callback status is already determined so should never get here
break
}
}
So I'm looking at the Photos API and Apple's sample code here
https://developer.apple.com/library/ios/samplecode/UsingPhotosFramework/Introduction/Intro.html
and its conversion to swift here
https://github.com/ooper-shlab/SamplePhotosApp-Swift
I have integrated the code into my project so that a collectionView is successfully updating itself form the library as I take photos. There is one quirk: Sometimes cells are blank, and it seems to be connected to stopCachingImagesForAllAssets which Apple calls each time the library is updated at the end of photoLibraryDidChange delegate method.
I can remove the line and it fixes the problem, but surely there is a reason Apple put it there in the first place? I am concerned with memory usage.
// MARK: - PHPhotoLibraryChangeObserver
func photoLibraryDidChange(changeInstance: PHChange) {
// Check if there are changes to the assets we are showing.
guard let
assetsFetchResults = self.assetsFetchResults,
collectionChanges = changeInstance.changeDetailsForFetchResult(assetsFetchResults)
else {return}
/*
Change notifications may be made on a background queue. Re-dispatch to the
main queue before acting on the change as we'll be updating the UI.
*/
dispatch_async(dispatch_get_main_queue()) {
// Get the new fetch result.
self.assetsFetchResults = collectionChanges.fetchResultAfterChanges
let collectionView = self.pictureCollectionView!
if !collectionChanges.hasIncrementalChanges || collectionChanges.hasMoves {
// Reload the collection view if the incremental diffs are not available
collectionView.reloadData()
} else {
/*
Tell the collection view to animate insertions and deletions if we
have incremental diffs.
*/
collectionView.performBatchUpdates({
if let removedIndexes = collectionChanges.removedIndexes
where removedIndexes.count > 0 {
collectionView.deleteItemsAtIndexPaths(removedIndexes.aapl_indexPathsFromIndexesWithSection(0))
}
if let insertedIndexes = collectionChanges.insertedIndexes
where insertedIndexes.count > 0 {
collectionView.insertItemsAtIndexPaths(insertedIndexes.aapl_indexPathsFromIndexesWithSection(0))
}
if let changedIndexes = collectionChanges.changedIndexes
where changedIndexes.count > 0 {
collectionView.reloadItemsAtIndexPaths(changedIndexes.aapl_indexPathsFromIndexesWithSection(0))
}
}, completion: nil)
}
self.resetCachedAssets() //perhaps prevents memory warning but causes the empty cells
}
}
//MARK: - Asset Caching
private func resetCachedAssets() {
self.imageManager?.stopCachingImagesForAllAssets()
self.previousPreheatRect = CGRectZero
}
I was having the same result.
Here's what fixed the issue for me:
Since performBatchUpdates is asynchronous, the resetCachedAssets gets executed possibly while the delete/insert/reload is happening, or even between those.
That didn't sound nice to me. So I moved the line:
self.resetCachedAssets()
to the first line of the dispatch_async block.
I hope this helps you too.
Does any body know what I need to check if app freezes after some time? I mean, I can see the app in the iPhone screen but no view responds.
I did some google and i found that, i've blocked the main thread somehow.
But my question is how to identify which method causes blocking of main thread? is there any way to identify?
Launch your app and wait for it to freeze. Then press the "pause" button in Xcode. The left pane should show you what method is currently running.
Generally, it is highly recommended to perform on the main thread all animations method and interface manipulation, and to put in background tasks like download data from your server, etc...
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//here everything you want to perform in background
dispatch_async(dispatch_get_main_queue(), ^{
//call back to main queue to update user interface
});
});
Source : http://www.raywenderlich.com/31166/25-ios-app-performance-tips-tricks
Set a break point from where the freeze occurs and find which line cause that.
Chances may be,Loading of large data,disable the controls,overload in main thread,Just find out where that occurs using breakpoints and rectify based on that.
I believe it should be possible to periodically check to see if the main thread is blocked or frozen. You could create an object to do this like so:
final class FreezeObserver {
private let frequencySeconds: Double = 10
private let acceptableFreezeLength: Double = 0.5
func start() {
DispatchQueue.global(qos: .background).async {
let timer = Timer(timeInterval: self.frequencySeconds, repeats: true) { _ in
var isFrozen = true
DispatchQueue.main.async {
isFrozen = false
}
DispatchQueue.global(qos: .background).asyncAfter(deadline: .now() + self.acceptableFreezeLength) {
guard isFrozen else { return }
print("your app is frozen, so crash or whatever")
}
}
let runLoop = RunLoop.current
runLoop.add(timer, forMode: .default)
runLoop.run()
}
}
}
Update October 2021:
Sentry now offers freeze observation, if you don't wanna roll this yourself.
I reached an error similar to this, but it was for different reasons. I had a button that performed a segue to another ViewController that contained a TableView, but it looked like the application froze whenever the segue was performed.
My issue was that I was infinitely calling reloadData() due to a couple of didSet observers in one of my variables. Once I relocated this call elsewhere, the issue was fixed.
Most Of the Time this happened to me when a design change is being called for INFINITE time. Which function can do that? well it is this one:
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
}
Solution is to add condition where the function inside of viewDidLayoutSubviews get calls only 1 time.
It could be that another view is not properly dismissed and it's blocking user interaction! Check the UI Debugger, and look at the top layer, to see if there is any strange thing there.