问题
Here's high level description of what I'm trying to achieve; 1. fetch data 2. save the fetched data in an array object 3. update collection view with the size of the array
Here's my code
class ItemcollectionViewController:UICollectionViewController, UICollectionViewDelegateFlowLayout {
let cellId = "CellId"
var categories = [Category]()
let viewOptionVar:ViewOptionBar = {
let vOV = ViewOptionBar()
vOV.translatesAutoresizingMaskIntoConstraints = false
return vOV
}()
private func fetchData() {
let categoryController = CategoryController()
categoryController.getAllCategory(username: "blah", password: "password") {(returnedCategories, error) -> Void in
if error != nil {
print(error)
return
}
self.categories = returnedCategories!
print("size of the array is \(self.categories.count)")
OperationQueue.main.addOperation{self.collectionView?.reloadData()}
}
}
override func viewDidLoad() {
super.viewDidLoad()
fetchData()
collectionView?.backgroundColor = UIColor.white
collectionView?.register(ItemCell.self, forCellWithReuseIdentifier: cellId)
collectionView?.contentInset = UIEdgeInsetsMake(50, 0, self.view.frame.height, self.view.frame.width)
collectionView?.scrollIndicatorInsets = UIEdgeInsetsMake(50, 0, 0, self.view.frame.width)
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
print("in the method \(self.categories.count)")
return self.categories.count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! ItemCell
cell.category = categories[indexPath.item]
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: 111, height: 111)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return 0
}
private func setupViweOptionBar() {
view.addSubview(viewOptionVar)
view.addConstraintsWithFormat(format: "H:|[v0]|", views: viewOptionVar)
view.addConstraintsWithFormat(format: "V:|[v0(50)]", views: viewOptionVar)
}
}
In the log I could see the following statements:
in the method 0
size of the array is 3
and could not see any cell from my view.
Can someone advise me what I've done wrong? Thanks in advance.
EDIT 1 Now I'm fetching data after registering the customised cells. However, it still doesn't work
updated code:
class ItemcollectionViewController:UICollectionViewController, UICollectionViewDelegateFlowLayout {
let cellId = "CellId"
var categories = [Category]()
let viewOptionVar:ViewOptionBar = {
let vOV = ViewOptionBar()
vOV.translatesAutoresizingMaskIntoConstraints = false
return vOV
}()
private func fetchData() {
let categoryController = CategoryController()
categoryController.getAllCategory(username: "blah", password: "password") {(returnedCategories, error) -> Void in
if error != nil {
print(error)
return
}
self.categories = returnedCategories!
print("size of the array is \(self.categories.count)")
}
}
override func viewDidLoad() {
super.viewDidLoad()
collectionView?.backgroundColor = UIColor.white
collectionView?.register(ItemCell.self, forCellWithReuseIdentifier: cellId)
collectionView?.contentInset = UIEdgeInsetsMake(50, 0, self.view.frame.height, self.view.frame.width)
collectionView?.scrollIndicatorInsets = UIEdgeInsetsMake(50, 0, 0, self.view.frame.width)
collectionView?.dataSource = self
collectionView?.delegate = self
fetchData()
DispatchQueue.main.async{self.collectionView?.reloadData()}
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
print("in the method \(self.categories.count)")
return self.categories.count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! ItemCell
cell.category = categories[indexPath.item]
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: 111, height: 111)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return 0
}
private func setupViweOptionBar() {
view.addSubview(viewOptionVar)
view.addConstraintsWithFormat(format: "H:|[v0]|", views: viewOptionVar)
view.addConstraintsWithFormat(format: "V:|[v0(50)]", views: viewOptionVar)
}
}
EDIT 2
The following code is my querying method
func getAllCategory(username:String, password:String, callback: @escaping ([Category]?, String?) -> Void){
var categories = [Category]()
let fetchCategories = URL(string: userURL + "all")
URLSession.shared.dataTask(with: fetchCategories!, completionHandler: { (data, response, error) in
if let err = error {
print(err)
return
}
do {
let jsonCategoryObj = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as! [[String: AnyObject]]
for categoryDictionary in jsonCategoryObj {
let category = Category()
category.categoryId = categoryDictionary["categoryId"] as? String
category.categoryName = categoryDictionary["categoryName"] as? String
category.categoryDescription = categoryDictionary["categoryDescription"] as? String
let categoryRegisteredDateString = categoryDictionary["categoryRegisteredDate"] as? String
let df = DateFormatter()
df.dateFormat = self.shapeDateFormat
let categoryRegisteredDate = df.date(from: categoryRegisteredDateString!)!
category.categoryRegisteredDate = categoryRegisteredDate
categories.append(category)
}
callback(categories, nil)
}catch let jsonError {
callback(nil, String(describing: jsonError))
}
}).resume()
}
FYI: I know I'm not using passed user credential, it's just a copy and paste error from my different query method
回答1:
I'm not sure how this resolved this issue. But I just added
print("size of the array is \(self.categories?.count)")
just next to
OperationQueue.main.addOperation{self.collectionView?.reloadData()}
and it magically works.. even thought when I go back and come back to the screen, it does not show anything.
I'll investigate it more and try to find out why this is happening
Updated
Using
DispatchQueue.main.sync
instead of
DispatchQueue.main.async
resolved the problem.
回答2:
When the DataSource changes, reloadData does not update the cell that has been displayed in the view. Reload visible items will do this job.
self.collectionView.reloadData()
self.collectionView.performBatchUpdates({ [weak self] in
let visibleItems = self?.collectionView.indexPathsForVisibleItems ?? []
self?.collectionView.reloadItems(at: visibleItems)
}, completion: { (_) in
})
回答3:
DispatchQueue.main.async{self.collectionView?.reloadData()}
collectionView?.backgroundColor = UIColor.white
collectionView?.register(ItemCell.self, forCellWithReuseIdentifier: cellId)
You are reloading data before you even have registered your cell.
Register your cell and datasource and delegate methods FIRST, and reload data LAST.
EDIT:
I see you edited your post.
But again, you are fetchData() before you even have registered your cell. So, again, move the fetchData method AFTER you have registered all cells , datasources and delegates.
来源：https://stackoverflow.com/questions/42241629/uicollectionview-reloaddata-does-not-update-cells-in-the-collection-view