UICollectionView reloadData() 不会更新集合视图中的单元格 [英] UICollectionView reloadData() does not update cells in the collection view
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问题描述
这是我要实现的目标的高级描述；1. 获取数据2.将获取的数据保存在一个数组对象中3. 用数组的大小更新集合视图
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
这是我的代码
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)
}
}
在日志中我可以看到以下语句:
In the log I could see the following statements:
在方法0中
数组大小为 3
在我看来看不到任何单元格.
and could not see any cell from my view.
有人可以告诉我我做错了什么吗?提前致谢.
Can someone advise me what I've done wrong? Thanks in advance.
编辑 1现在我在注册自定义单元后获取数据.但是还是不行
EDIT 1 Now I'm fetching data after registering the customised cells. However, it still doesn't work
更新代码:
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)
}
}
编辑 2
以下代码是我的查询方法
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()
}
仅供参考:我知道我没有使用传递的用户凭据，这只是我不同查询方法的复制和粘贴错误
FYI: I know I'm not using passed user credential, it's just a copy and paste error from my different query method
推荐答案
DataSource 更改时，reloadData 不会更新视图中已显示的单元格.重新加载可见项目将完成这项工作.
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
})
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