I have a following code structure, how can I run this code on background thread and execute all the methods serially in FIFO.
How to wait for function to executes all its statements and then move to next function?
func downloadImagesAndProcess(){
// i need these methods to execute one by one i.e when saveimages completes fully only then call resizeimages
saveImages()
resizeImages()
shareImgs()
}
func saveImages(){
// long async tasks
for (index, image) in (self.images.enumerated())! {
KingfisherManager.shared.retrieveImage(with: URL(string:image.imageFile)!) { result in
switch result {
case .success(let value):
self.saveImageDocumentDirectory(image: value.image, imageName: imgNameStr)
case .failure(let error):
print(error) // The error happens
}
}
}
}
func resizeImages(){
// long running tasks
}
func shareimgs(){
//share
}
I need these methods to execute one by one i.e. when saveImages completes fully only then call resizeImages
How to wait for function to executes all its statements and then move to next function?
The easiest thing to do is call the next method inside the completion of the previous one
func saveImages(){
let group = DispatchGroup()
for (index, image) in (self.images.enumerated())! {
group.enter()
KingfisherManager.shared.retrieveImage(with: URL(string:image.imageFile)!) { result in
switch result {
case .success(let value):
self.saveImageDocumentDirectory(image: value.image, imageName: imgNameStr)
case .failure(let error):
print(error) // The error happens
}
group.leave()
}
}
group.notify(queue: .main) {
// do your stuff, check if every image has been downloaded
self.resizeImages() // this will be called after the completion of the current task
}
}
Then in the resizeImages I guess there's another completion handler, inside that you'll call shareImgs