I'm trying to use prefetching which was introduced in iOS 10. But unable to achieve it.
I do set the delegate and enable the prefetching. But when i set a breakpoint or console log at prefetch, it does not pass through the function ever.
I know on fast scroll, the prefetching is skipped. but even on slowest scroll, its never been called
var dataSource = [IndexPath: Any]()
override func viewDidLoad() {
if #available(iOS 10.0, *) {
mainCollectionView.isPrefetchingEnabled = true
mainCollectionView.prefetchDataSource = self
}
//Other stuffs
}
//This is not being called
func collectionView(_ collectionView: UICollectionView, prefetchItemsAt indexPaths: [IndexPath]) {
print("Prefectch")
for indexPath in indexPaths {
dataSource[indexPath] = fetchDataSource(indexPath)
}
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "MyCell", for: indexPath) as! MyCell
cell.dataSource = dataSource[indexPath] ?? fetchDataSource(indexPath)
return cell
}
Call
override func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
self.collectionView(collectionView, prefetchItemsAt: [indexPath])
}
To trigger the prefetch, and remove:
collectionViewLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
If you have it.
This was by me the case.
Related
I need to use moveItem(at:to:) delegate method in order to move my collection view cells.
When I implement the data source delegation methods it's working fine, but I need to set my data source as UICollectionViewDiffableDataSource and in this way the moveItem(at:to:) did not call.
Any solution to handle,
This way it's work when using delegations :
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 10
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! CustomCell
cell.textLabel.text = "Some value"
return cell
}
override func collectionView(_ collectionView: UICollectionView, canMoveItemAt indexPath: IndexPath) -> Bool {
true
}
override func collectionView(_ collectionView: UICollectionView, moveItemAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {
print("OK")
}
set data source in this way is not work
func setupDataSource() {
dataSource = UICollectionViewDiffableDataSource<Section, Person>(collectionView: collectionView, cellProvider: {
(collectionView: UICollectionView, indexPath: IndexPath, person: Person) -> UICollectionViewCell? in
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! CustomCell
cell.textLabel.text = "Some text"
return cell
})
}
For custom behavior create a subclass of UICollectionViewDiffableDataSource and override the methods there.
I am new to iOS and I want to implement a UICollectionView inside a UITableView which can have multiple select/unselect in section 1 of the UITableview. And in section 2, only a single selection is allowed. And save the selection sate event if I dismiss the Viewcontroller and when I open it again, it must show the last selected cell as highlight.
I searched for tutorials but all of them don't mention to select/unselect the state of collection cell or saving state after dismissing view controller.
Can someone help to implement it?
Thank in advance!
Here is my code I do till now:
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return clvData.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "clvCell", for: indexPath) as! demoCollectionViewCell
cell.title.text = clvData[indexPath.item] as? String
return cell
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let cell = collectionView.cellForItem(at: indexPath)
cell?.backgroundColor = .red
}
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
let cell = collectionView.cellForItem(at: indexPath)
cell?.backgroundColor = .white
}
you guys can also check my project here:
https://mega.nz/#!xRs0EQyQ
try this and let me know if you have any problem or if this solved your problem.
var arrSelectedIndex:[IndexPath] = []// store this array either in database by api or in local
var clvData:[String] = []// your data array
//get the arrSelectedIndex from default in viewDidLoad before reloading the table and collection.
override func viewDidLoad() {
super.viewDidLoad()
if let myArray = UserDefaults.standard.array(forKey: "selectedArray") as? [IndexPath] {
arrSelectedIndex = myArray
} else {
arrSelectedIndex = []
}
}
// and save the arrSelectedIndex in viewWillDisappear method
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
UserDefaults.standard.set(arrSelectedIndex, forKey: "selectedArray")
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return clvData.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "clvCell", for: indexPath) as! demoCollectionViewCell
cell.title.text = clvData[indexPath.item] as? String
if arrSelectedIndex.contains(indexPath) { // You need to check wether selected index array contain current index if yes then change the color
cell.backgroundColor = UIColor.red
}
else {
cell.backgroundColor = UIColor.white
}
return cell
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let cell = collectionView.cellForItem(at: indexPath)
cell?.backgroundColor = .red
if !arrSelectedIndex.contains(indexPath) {// if it does not contains the index then add it
arrSelectedIndex.append(indexPath)
}
}
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
let cell = collectionView.cellForItem(at: indexPath)
cell?.backgroundColor = .white
if let currIndex = arrSelectedIndex.firstIndex(of: indexPath) {// if it contains the index then delete from array
arrSelectedIndex.remove(at: currIndex)
}
}
I am developing appleTV application.
I have a UICollectionView inside a UICollectionView cell.
When the data is updated, the CollectionView placed in the ViewController is reloadData, and at the same time, the CollectionView in the CollectionView is also reloadData.
Then focus does not return to the original position in CollectionView.
The CollectionView placed in the ViewController is canFocusItemAt false.
What should I do?
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
if collectionView === self.collectionView {
return 10
} else {
return 10
}
}
func collectionView(_ collectionView: UICollectionView, canFocusItemAt indexPath: IndexPath) -> Bool {
if collectionView === self.collectionView {
return false
} else {
return true
}
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if collectionView === self.collectionView {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "aaaa", for: indexPath)
if let collectionView = cell.viewWithTag(20) as? UICollectionView {
collectionView.delegate = self
collectionView.dataSource = self
collectionView.reloadData()
}
return cell
} else {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "bbbb", for: indexPath)
return cell
}
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
self.collectionView.reloadData()
}
Have an issue where:
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath)
is called when an item is selected, but I cannot change any cell properties from this method.
I created a new project with a stripped down UICollectionViewController to change the background color of a cell when selected. It also doesn't work. Here it is:
import UIKit
private let reuseIdentifier = "Cell"
class CollectionViewController: UICollectionViewController {
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 5
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath)
cell.backgroundColor = UIColor.blue
return cell
}
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let cell = self.collectionView(self.collectionView, cellForItemAt: indexPath)
cell.backgroundColor = UIColor.green
}
}
The only thing I did in Storyboard is delete the standard View Controller and replace it with a UICollectionViewController, create a subclass of UICollectionViewController and set the controller in the storyboard as that class.
Also, I can confirm that the cell's index path is returned from this method when called from inside the didSelectItemAt method:
self.collectionView.indexPathsForSelectedItems
You are using the wrong API. Never call the delegate method collectionView(_ cellForItemAt:, use cellForItem(at:
if let cell = collectionView.cellForItem(at: indexPath) {
cell.backgroundColor = UIColor.green
}
But be aware that this change is not persistent. When the user scrolls the color will change back to blue.
You can achieve that as below,
ViewController
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ColoursViewCell", for: indexPath) as! ColoursViewCell
return cell
}
UICollectionViewCell
class ColoursViewCell: UICollectionViewCell {
#IBOutlet var photoImageView: UIImageView?
override var bounds: CGRect {
didSet {
self.layoutIfNeeded()
}
}
override var isSelected: Bool{
didSet{
if self.isSelected{
self.photoImageView?.backgroundColor = UIColor.random
}else{
self.photoImageView?.backgroundColor = UIColor.lightGray
}
}
}
}
you can have sample projects from this link I have in GitHub
https://github.com/hadanischal/RandomColors/tree/develop
I am using Swift4 and Xcode9.
I create my collectionView cells by using the delegate method below;
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "mediaItemCell", for: indexPath) as! MediaItemCollectionViewCell
cell.mediaItemCellImageView.image = mediaPlayer?.item(at: indexPath.row)?.image
return cell
}
Then, I want to replace the image of selected cell with a "stop" image. To achieve this, I have tried to use didSelectItemAt method;
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
if (mediaPlayer?.isPlaying == true) {
// stop the player
mediaPlayer?.stopPlayingMedia()
} else {
// change the image and start playing
let cell = collectionView.cellForItem(at: indexPath) as! MediaItemCollectionViewCell // CRASH
cell.mediaItemCellImageView.image = UIImage(named: "stop.png")
...
...
}
}
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
// restore the original image
let cell = collectionView.cellForItem(at: indexPath) as! MediaItemCollectionViewCell
cell.mediaItemCellImageView.image = mediaPlayer?.item(at: indexPath.row)?.image
// stop playing
mediaPlayer?.stopPlayingMedia()
}
Now, when I select the cell which is already selected (hence the original image has already been replaced with "stop.png") the code above works; i.e. the original image is restored, which is done by stopPlayingMedia() method.
When I select a cell different than the currently selected one, the App crashes. I tried to move the didSelectItemAt call out of the delegate method, but it did not work.
Surprisingly, the logical check if collectionView.cellForItem(at: indexPath) is MediaItemCollectionViewCell succeeds when I select the currently selected cell, and fails when I select another cell.
I want to change the image of the cell, hence need to cast the variable type but it fails. Why does to cast fail when I select a different cell than the currently selected one?
Thanks
Edit:
I use collectionView.reloadData() to restore all the images to originals (I mentioned this in the OP - when stopPlayingMedia() is invoked). It appears that, if I add a private var index:IndexItem? to my ViewController class and update its value within didSelectItemAt (to save the last selected cell) and use the code below, the code does not crash
extension ViewController:MediaPlayerControllerDelegate {
// this delegate method is invoked when stopPlayingMedia() is called
func mediaPlayerControllerDidFinishPlaying() {
// restore the UI
// collectionView.reloadData() -> this causes the crash, instead, I only restore one cell
let cell = collectionView.cellForItem(at: index!) as! MediaItemCollectionViewCell
cell.mediaItemCellImageView.image = mediaPlayer?.item(at: (index?.row)!)?.image
timeLabel.text = "00:00"
progressBar.progress = 0.0
}
}
I tried the following to create cell and changing the image inside cell on selection. Not crashing at all. Please check the implementation, It might help you.
import UIKit
class ViewController: UIViewController {
private var isPlayingModel = [false, false, false, false, false] // initially all are stop, not playing
#IBOutlet weak var collectionView: UICollectionView! {
didSet{
collectionView.delegate = self
collectionView.dataSource = self
}
}
}
extension ViewController: UICollectionViewDataSource {
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return isPlayingModel.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "mediaItemCell", for: indexPath) as! MediaItemCollectionViewCell
cell.imageVw.image = isPlayingModel[indexPath.row] ? #imageLiteral(resourceName: "start") : #imageLiteral(resourceName: "stop")
return cell
}
}
extension ViewController: UICollectionViewDelegate {
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
isPlayingModel[indexPath.row] = !isPlayingModel[indexPath.row]
let cell = collectionView.cellForItem(at: indexPath) as! MediaItemCollectionViewCell
cell.imageVw.image = isPlayingModel[indexPath.row] ? #imageLiteral(resourceName: "start") : #imageLiteral(resourceName: "stop")
}
}
extension ViewController: UICollectionViewDelegateFlowLayout {
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: view.frame.size.width, height: 60)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
return 4
}
}
class MediaItemCollectionViewCell: UICollectionViewCell {
#IBOutlet weak var imageVw: UIImageView!
}
Check the implementation here.
You are not passing indexPath correctly to load a cell, that's why it is crashing.Edit your didSelectItemAt: method as follows:
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let selectedCell = IndexPath(item: indexPath.item, section: indexPath.section)
let cell = collectionView.cellForItem(at: selectedCell) as! ACollectionViewCell
cell.imgView.image = UIImage(named: "3.jpg")
}
Collection view indexPath has element item, and not row
Try this and see: (let me know what does it print)
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
// restore the original image
if let cell = collectionView.cellForItem(at: indexPath) as? MediaItemCollectionViewCell {
if let cellImage = mediaPlayer?.item(at: indexPath.item)?.image { // Collection view indexPath has element `item`, and not `row`
cell.mediaItemCellImageView.image = cellImage
} else {
print("cellImage not found at indexPath - \(indexPath)")
}
} else {
print("collection view cell `MediaItemCollectionViewCell` not found at indexPath -\(indexPath) ")
}
// stop playing
mediaPlayer?.stopPlayingMedia()
}