I searched a lot but I can't find a good explanation of using a determinate circular progress indicator.
I have a Helper-Class that converts a PDF to an image. I have more than 400 pages so I decided to make these things asynchron with the following code:
DispatchQueue.concurrentPerform(iterations: pdfDocument.numberOfPages) { i in
… do the work …
view.incrementProgressIndicator()
}
Insight the view, where the ProgressIndicator lives, the called function looks the following:
func incrementProgressIndicator() {
self.progressIndicator.increment(by: 1)
}
For sure, Swift says: "UI API called on a background thread".
I tried to surround the code of incrementing with:
DispatchQueue.main.async {
self.progressIndicator.increment(by: 1)
}
But now, all the work of indicating is done after the conversion of PDF is completed.
Can someone tell my how this can be done? I can't find a working tutorial for my issue.
Thank you for your help!
I found the solution for my issue. I replace the
DispatchQueue.concurrentPerform(iterations: pdfDocument.numberOfPages) { i in
… do the work …
view.incrementProgressIndicator()
}
with the following code:
for i in 0..<pdfDocument.numberOfPages {
DispatchQueue.global(qos: .background).async {
let pdfPage = pdfDocument.page(at: i + 1)!
if let result = self.convertPageToImage(withPdfPage: pdfPage, sourceURL: sourceURL, destUrl: destinationURL, index: i) {
urls[i] = result
}
DispatchQueue.main.async {
if let delegate = self.delegate {
print("Ask for Increment")
delegate.incrementProgressIndicator()
}
}
}
}
Related
I am trying to create a Robotic Process Automation tool for Macos using Swift. Users create an Automation that is an array of Step objects and then play it. One of the subclasses of Step is Pause which is supposed to pause the execution for a given number of seconds.
For some reason, execution hangs when I use the DispatchQueue.main.asyncAfter() method in the Pause class. Usually the first run through the automation is fine, but when it goes to repeat, it eventually hangs for much longer. The error goes away when I use sleep() instead.
The other weird thing about this bug is when I open Xcode to try and see what is happening, the hang resolves and execution continues. I am wondering if the process enters background somehow and then the DispatchQueue.main.asyncAfter() doesn't work. I have tried to change the Info.plist "Application does not run in background" to YES, but this doesn't have any effect.
The problem with using sleep() is it blocks the UI thread so users can't stop the automation if they need to. I have tried lots of different variations of threading with DispatchQueue, but it always seems to hang somewhere on repeat execution. I have also tried using a Timer.scheduledTimer() instead of DispatchQueue but that hangs as well. I'm sure I'm missing something simple, but I can't figure it out.
Creating the Step Array and Starting Automation
class AutomationPlayer {
static let shared = AutomationPlayer()
var automation: Automation?
var stepArray: [Step] = []
func play() {
// Create array of steps
guard let steps = automation?.steps, let array = Array(steps) as? [Step] else {
return
}
// If the automation repeats, add more steps to array.
for _ in 0..<(automation?.numberOfRepeats ?? 1) {
for (index, step) in array.enumerated() {
stepArray.append(step)
}
}
// Add small delay to allow window to close before execution.
DispatchQueue.main.asyncAfter(deadline: .now() + 0.4) { [weak self] in
self?.execute(index: 0)
}
}
private func execute(index: Int) {
let step = stepArray[index]
executeStep(step: step) { [weak self] success, error in
guard error == nil else { return }
let newIndex = index + 1
if newIndex < self?.stepArray.count ?? 0 {
//Need a small delay between steps otherwise execution is getting messed up.
usleep(400000)
self?.execute(index: newIndex)
} else {
self?.stepArray = []
}
}
}
private func executeStep(step: Step?, completionHandler: #escaping (Bool, Error?) -> Void) -> Void {
step?.execute(completionHandler: { [weak self] success, error in
guard error == nil else {
completionHandler(false, error)
return
}
completionHandler(true, nil)
})
}
Pause Class
#objc(Pause)
public class Pause: Step {
override func execute(completionHandler: #escaping (Bool, Error?) -> Void) {
print("Pause for: \(self.time) seconds")
// This will eventually hang when the automation repeats itself
DispatchQueue.main.asyncAfter(deadline: .now() + Double(self.time)) {
completionHandler(true, nil)
})
// This will also hang
Timer.scheduledTimer(withTimeInterval: self.time, repeats: false) { timer in
completionHandler(true, nil)
}
// If I use this instead, the automation repeats just fine
sleep(UInt32(self.time))
completionHandler(true, nil)
}
}
So I think I figured it out. MacOS was putting my app into AppNap after a certain period of time which would cause the DispatchQueue.main.async() to stop working. For some reason, AppNap does not affect delays when you use sleep()
I found an answer here
This answer was a little older. I am using SwiftUI to build my mac app so I added this my #main struct
#main
struct Main_App: App {
#State var activity: NSObjectProtocol?
var body: some Scene {
WindowGroup("") {
MainWindow()
.onAppear {
activity = ProcessInfo().beginActivity(options: .userInitiated, reason: "Good Reason")
}
}
}
This seems to prevent the app from going into AppNap and the automation continues. It's pretty ugly, but it works.
I am writing a Safari app extension and want to fetch the URL for the active page in my view controller.
This means nested completion handlers to fetch the window, to fetch the tab, to fetch the page, to access its properties. Annoying but simple enough. It looks like this:
func doStuffWithURL() {
var url: URL?
SFSafariApplication.getActiveWindow { (window) in
window?.getActiveTab { (tab) in
tab?.getActivePage { (page) in
page?.getPropertiesWithCompletionHandler { (properties) in
url = properties?.url
}
}
}
}
// NOW DO STUFF WITH THE URL
NSLog("The URL is \(String(describing: url))")
}
The obvious problem is it does not work. Being completion handlers they will not be executed until the end of the function. The variable url will be nil, and the stuff will be done before any attempt is made to get the URL.
One way around this is to use a DispatchQueue. It works, but the code is truly ugly:
func doStuffWithURL() {
var url: URL?
let group = DispatchGroup()
group.enter()
SFSafariApplication.getActiveWindow { (window) in
if let window = window {
group.enter()
window.getActiveTab { (tab) in
if let tab = tab {
group.enter()
tab.getActivePage { (page) in
if let page = page {
group.enter()
page.getPropertiesWithCompletionHandler { (properties) in
url = properties?.url
group.leave()
}
}
group.leave()
}
}
group.leave()
}
}
group.leave()
}
// NOW DO STUFF WITH THE URL
group.notify(queue: .main) {
NSLog("The URL is \(String(describing: url))")
}
}
The if blocks are needed to know we are not dealing with a nil value. We need to be certain a completion handler will return, and therefore a .leave() call before we can call a .enter() to end up back at zero.
I cannot even bury all that ugliness away in some kind of getURLForPage() function or extension (adding some kind of SFSafariApplication.getPageProperties would be my preference) as obviously you cannot return from a function from within a .notify block.
Although I tried creating a function using queue.wait and a different DispatchQueue as described in the following answer to be able to use return…
https://stackoverflow.com/a/42484670/2081620
…not unsurprisingly to me it causes deadlock, as the .wait is still executing on the main queue.
Is there a better way of achieving this? The "stuff to do," incidentally, is to update the UI at a user request so needs to be on the main queue.
Edit: For the avoidance of doubt, this is not an iOS question. Whilst similar principles apply, Safari app extensions are a feature of Safari for macOS only.
Thanks to Larme's suggestions in the comments, I have come up with a solution that hides the ugliness, is reusable, and keep the code clean and standard.
The nested completion handlers can be replaced by an extension to the SFSafariApplication class so that only one is required in the main body of the code.
extension SFSafariApplication {
static func getActivePageProperties(_ completionHandler: #escaping (SFSafariPageProperties?) -> Void) {
self.getActiveWindow { (window) in
guard let window = window else { return completionHandler(nil) }
window.getActiveTab { (tab) in
guard let tab = tab else { return completionHandler(nil) }
tab.getActivePage { (page) in
guard let page = page else { return completionHandler(nil) }
page.getPropertiesWithCompletionHandler { (properties) in
return completionHandler(properties)
}
}
}
}
}
}
Then in the code it can be used as:
func doStuffWithURL() {
SFSafariApplication.getActivePageProperties { (properties) in
if let url = properties?.url {
// NOW DO STUFF WITH THE URL
NSLog("URL is \(url))")
} else {
// NOW DO STUFF WHERE THERE IS NO URL
NSLog("URL ERROR")
}
}
}
I'm using Alamofire and a serial DispatchQueue to try and upload one image at a time from an array of images. I would like to upload one at a time so I can update a single progress HUD as each upload goes through. My code looks something like this:
let serialQueue = DispatchQueue(label: "project.serialQueue")
for image in images {
serialQueue.async {
uploadImage(image: image, progress: { progress in
//update progress HUD
}, completion: { json, error in
//dismiss HUD
})
}
}
The problem is that my uploadImage() calls are all executing at once. I think this is because Alamofire requests are run asynchronously. Any ideas on how to best solve this?
Alamofire runs in his own background queue , so You can try
var counter = 0
func uploadImg(_ img:UIImage) {
uploadImage(image: img, progress: { progress in
//update progress HUD
}, completion: { json, error in
//dismiss HUD
self.counter += 1
if self.counter < images.count {
self.uploadImg(images[counter])
}
})
}
Call
uploadimg(images.first!)
I am trying to convert image snapshots into a video but I am facing UI Thread problems: my view controller is locked. I would like to know how to handle this because I did a lot of research and tried to detach the process into different DispatchQueues but none of them worked. So, it explains why I am not using any Queue on the code below:
class ScreenRecorder {
func renderPhotosAsVideo(callback: #escaping(_ success: Bool, _ url: URL)->()) {
var frames = [UIImage]()
for _ in 0..<100 {
let image = self.containerView.takeScreenshot()
if let imageData = UIImageJPEGRepresentation(image, 0.7), let compressedImage = UIImage(data: imageData) {
frames.append(compressedImage)
}
}
self.generateVideoUrl(frames: frames, complete: { (fileURL: URL) in
self.saveVideo(url: fileURL, complete: { saved in
print("animation video save complete")
callback(saved, fileURL)
})
})
}
}
extension UIView {
func takeScreenshot() -> UIImage {
let renderer = UIGraphicsImageRenderer(size: self.bounds.size)
let image = renderer.image { _ in
self.drawHierarchy(in: self.bounds, afterScreenUpdates: true)
}
return image
}
}
class ViewController {
let recorder = ScreenRecorder()
recorder.renderPhotoAsVideo { success, url in
if (success) {
print("ok")
} else {
self.alert(title: "Erro", message: "Nao foi possivel salvar o video", block: nil)
}
}
}
PS: I used this tutorial as reference -> http://www.mikitamanko.com/blog/2017/05/21/swift-how-to-record-a-screen-video-or-convert-images-to-videos/
It really looks like this is not possible, at least not the way you are trying to do it.
There are quite a few ways to render a UIViews content into an image, but all of them must be used from the main thread only. This applies also to the drawInHierarchy method you are using.
As you have to call it on the main thread and the method is just getting called so many times, I think this will never work in a performant way.
See profiling in Instruments:
Sources:
How to render view into image faster?
Safe way to render UIVIew to an image on background thread?
I'm trying to use Apple's AVMIDIPlayer object for playing a MIDI file. It seems easy enough in Swift, using the following code:
let midiFile:NSURL = NSURL(fileURLWithPath:"/path/to/midifile.mid")
var midiPlayer: AVMIDIPlayer?
do {
try midiPlayer = AVMIDIPlayer(contentsOf: midiFile as URL, soundBankURL: nil)
midiPlayer?.prepareToPlay()
} catch {
print("could not create MIDI player")
}
midiPlayer?.play {
print("finished playing")
}
And it plays for about 0.05 seconds. I presume I need to frame it in some kind of loop. I've tried a simple solution:
while stillGoing {
midiPlayer?.play {
let stillGoing = false
}
}
which works, but ramps up the CPU massively. Is there a better way?
Further to the first comment, I've tried making a class, and while it doesn't flag any errors, it doesn't work either.
class midiPlayer {
var player: AVMIDIPlayer?
func play(file: String) {
let myURL = URL(string: file)
do {
try self.player = AVMIDIPlayer.init(contentsOf: myURL!, soundBankURL: nil)
self.player?.prepareToPlay()
} catch {
print("could not create MIDI player")
}
self.player?.play()
}
func stop() {
self.player?.stop()
}
}
// main
let myPlayer = midiPlayer()
let midiFile = "/path/to/midifile.mid"
myPlayer.play(file: midiFile)
You were close with your loop. You just need to give the CPU time to go off and do other things instead of constantly checking to see if midiPlayer is finished yet. Add a call to usleep() in your loop. This one checks every tenth of a second:
let midiFile:NSURL = NSURL(fileURLWithPath:"/Users/steve/Desktop/Untitled.mid")
var midiPlayer: AVMIDIPlayer?
do {
try midiPlayer = AVMIDIPlayer(contentsOfURL: midiFile, soundBankURL: nil)
midiPlayer?.prepareToPlay()
} catch {
print("could not create MIDI player")
}
var stillGoing = true
while stillGoing {
midiPlayer?.play {
print("finished playing")
stillGoing = false
}
usleep(100000)
}
You need to ensure that the midiPlayer object exists until it's done playing. If the above code is just in a single function, midiPlayer will be destroyed when the function returns because there are no remaining references to it. Typically you would declare midiPlayer as a property of an object, like a subclassed controller.
Combining Brendan and Steve's answers, the key is sleep or usleep and sticking the play method outside the loop to avoid revving the CPU.
player?.play({return})
while player!.isPlaying {
sleep(1) // or usleep(10000)
}
The original stillGoing value works, but there is also an isPlaying method.
.play needs something between its brackets to avoid hanging forever after completion.
Many thanks.