问题
I have tried to debug this but to no avail.
Basically when I segue from the first view controller to the second view controller the screen goes black momentarily. The code performs as I want it to but the screen going black is a bit of a pain for me.
Here is the code:
The segue from the first page:
func mapView(_ mapView: MGLMapView, tapOnCalloutFor annotation: MGLAnnotation) {
self.performSegue(withIdentifier: "goToSecond", sender: self)
}
second view controller:
override func viewDidLoad() {
super.viewDidLoad()
self.loadDataFromFirebase()
}
first function:
func loadDataFromFirebase() {
let db = Firestore.firestore()
db.collection(restaurauntName).getDocuments { (snapshot, err) in
if let err = err {
print("Error getting documents: \(err)")
return
} else {
for document in snapshot!.documents {
let name = document.get("Name") as! String
let description = document.get("Description") as! String
self.names.append(name)
self.descriptions.append(description)
}
self.setupImages() //safe to do this here as the firebase data is valid
self.collectionView?.reloadData()
}
}
}
this function sets up the page layout
func setupImages(){
self.pages = [
Page(imageName: self.imagesOne, headerText: names[0], bodyText: descriptions[0]),
Page(imageName: self.imagesTwo, headerText: names[1], bodyText: descriptions[1]),
Page(imageName: self.imagesThree, headerText: names[2], bodyText: descriptions[2]),
Page(imageName: self.imagesFour, headerText: names[3], bodyText: descriptions[3]),
Page(imageName: self.imagesFive, headerText: names[4], bodyText: descriptions[4]),
]
self.collectionView?.backgroundColor = .white
self.collectionView?.register(PageCell.self, forCellWithReuseIdentifier: "cellId")
self.collectionView?.isPagingEnabled = true
}
This sets up the page control
lazy var pageControl: UIPageControl = {
let pc = UIPageControl()
pc.currentPage = 0
pc.numberOfPages = 5
pc.currentPageIndicatorTintColor = .red
pc.pageIndicatorTintColor = .gray
return pc
}()
swiping controller extension:
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return 0
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return pages.count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cellId", for: indexPath) as! PageCell
let page = pages[indexPath.item]
cell.page = page
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: view.frame.width, height: view.frame.height)
}
Please let me know if I have to add anything else! any help is welcome
here is a youtube clip of the problem:
https://www.youtube.com/watch?v=vQGiw3Jd9pM
I have since found that when I comment out the firebase method the problem goes away.
回答1:
I have solved the problem! the problem was the order in which the functions were being called.
I realised not that the page was being set up too fast for firebase so I now call the function earlier! in the view will appear
override func viewWillAppear(_ animated: Bool) {
print("Done")
super.viewWillAppear(animated)
self.loadDataFromFirebase()
}
Thanks to all who helped!
回答2:
it seems your loadDataFromFirebase() method is taking a long time to execute on the main thread causing it to hung. Move your fetch to a background thread and update your UI once the data has been fetched in the meantime display a loading indicator or something of the sorts. Try:
func loadDataFromFirebase() {
DispatchQueue.global(qos: .userInitiated).async { [weak self] in
// Fetch and convert data
let db = Firestore.firestore()
...
DispatchQueue.main.async {
// Update your UI components with the data here
self.setupImages()
self.collectionView?.reloadData()
}
}
}
来源:https://stackoverflow.com/questions/59938683/screen-goes-black-after-segue