I have Collection view forming of 3 cells. I am displaying images on them, however, as fetching the image data from the server takes a few seconds, I use nsuserdefaults and cache.
let imagesFromUserDefaults
var dataIsFetched = false
viewDidLoad() {
let imagesFromUserDefaults = // Data from user defaults
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = self.collectionView.dequeueReusableCellWithReuseIdentifier("ACollectionViewCell", forIndexPath: indexPath) as! ACollectionViewCell
let activityView = UIActivityIndicatorView(activityIndicatorStyle: .Gray)
activityView.hidesWhenStopped = true
if dataIsFetched == false {
activityView.center = CGPointMake( cell.contentView.frame.size.width / 2, cell.contentView.frame.size.height / 2)
cell.contentView.addSubview(activityView)
activityView.startAnimating()
cell.img = // set image - works
} else {
// Data is fetched from the Server
activityView.stopAnimating()
cell.img = // set image - works
}
func fetchDataFromServer() {
// onSuccessResponse: Store into Array
dataIsFetched = true
collectionView.reloadData()
}
However, after the server data is loaded, even though the images change, the activity indicator doesn't go away. So if cells have the same indexPath.row (as proved by images as well), why doesn't it happen with activity indicator?
Also, is it more logical to place this behaviour to CollectionViewCell class? What is the proper way of handling
Edit:
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
if initialLoad {
count = self.defaults.count
} else {
count = self.fetched[0].count
}
print("number of cells \(count)")
if count < 4 {
return count
}
return 0
}
You need to set
let activityView = UIActivityIndicatorView(activityIndicatorStyle: .Gray)
activityView.hidesWhenStopped = true
Also you can set activityView.center = cell.center for a cleaner code.
You know, collect view cells are reusable, the 3 cells displayed in the collection view may share the same cell instance. So every time you call the cellForItemAtIndexPath method, you may get the same cell instance, and you repeatedly add an active indicator to the cell but never remove it. That's not good. Imagine what will you to indicate if an image is fetched with YES/NO, that'll be easy, if the image is fetched, you display YES in the cell, otherwise NO. So the indicator is here to do the same thing, the indicator's YES is animating and NO is not animating, don't get tricked because it's spinning, it's not for tracking the whole fetching process. All you need to do is to add the indicator in the prototype cell, and maintain the states of you images, fetched or not. And update the indicator base on the state:
var isImageFetched = yourImagesStates[indexPath.row];
if isImageFetched == true {
cell.indicator.stopAnimating()
cell.img = image
} else {
cell.indicator.startAnimating()
}
hope it'll help.
Related
First let me say this seems to be a common question on SO and I've read through every post I could find from Swift to Obj-C. I tried a bunch of different things over the last 9 hrs but my problem still exists.
I have a vc (vc1) with a collectionView in it. Inside the collectionView I have a custom cell with a label and an imageView inside of it. Inside cellForItem I have a property that is also inside the the custom cell and when the property gets set from datasource[indePath.item] there is a property observer inside the cell that sets data for the label and imageView.
There is a button in vc1 that pushes on vc2, if a user chooses something from vc2 it gets passed back to vc1 via a delegate. vc2 gets popped.
The correct data always gets passed back (I checked multiple times in the debugger).
The problem is if vc1 has an existing cell in it, when the new data is added to the data source, after I reload the collectionView, the label data from that first cell now shows on the label in new cell and the data from the new cell now shows on the label from old cell.
I've tried everything from prepareToReuse to removing the label but for some reason only the cell's label data gets confused. The odd thing is sometimes the label updates correctly and other times it doesn't? The imageView ALWAYS shows the correct image and I never have any problems even when the label data is incorrect. The 2 model objects that are inside the datasource are always in their correct index position with the correct information.
What could be the problem?
vc1: UIViewController, CollectionViewDataSource & Delegate {
var datasource = [MyModel]() // has 1 item in it from viewDidLoad
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: customCell, for: indexPath) as! CustomCell
cell.priceLabel.text = ""
cell.cleanUpElements()
cell.myModel = dataSource[indexPath.item]
return cell
}
// delegate method from vc2
func appendNewDataFromVC2(myModel: MyModel) {
// show spinner
datasource.append(myModel) // now has 2 items in it
// now that new data is added I have to make a dip to fb for some additional information
firebaseRef.observeSingleEvent(of: .value, with: { (snapshot) in
if let dict = snapshot.value as? [String: Any] else { }
for myModel in self.datasource {
myModel.someValue = dict["someValue"] as? String
}
// I added the gcd timer just to give the loop time to finish just to see if it made a difference
DispatchQueue.main.asyncAfter(deadline: .now() + 2, execute: {
self.datasource.sort { return $0.postDate > $1.postDate } // Even though this sorts correctly I also tried commenting this out but no difference
self.collectionView.reloadData()
// I also tried to update the layout
self.collectionView.layoutIfNeeded()
// remove spinner
}
})
}
}
CustomCell Below. This is a much more simplified version of what's inside the myModel property observer. The data that shows in the label is dependent on other data and there are a few conditionals that determine it. Adding all of that inside cellForItem would create a bunch of code that's why I didn't update the data it in there (or add it here) and choose to do it inside the cell instead. But as I said earlier, when I check the data it is always 100% correct. The property observer always works correctly.
CustomCell: UICollectionViewCell {
let imageView: UIImageView = {
let iv = UIImageView()
iv.translatesAutoresizingMaskIntoConstraints = false
return iv
}()
let priceLabel: UILabel = {
let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
return label
}()
var someBoolProperty = false
var myModel: MyModel? {
didSet {
someBoolProperty = true
// I read an answer that said try to update the label on the main thread but no difference. I tried with and without the DispatchQueue
DispatchQueue.main.async { [weak self] in
self?.priceLabel.text = myModel.price!
self?.priceLabel.layoutIfNeeded() // tried with and without this
}
let url = URL(string: myModel.urlStr!)
imageView.sd_setImage(with: url!, placeholderImage: UIImage(named: "placeholder"))
// set imageView and priceLabel anchors
addSubview(imageView)
addSubview(priceLabel)
self.layoutIfNeeded() // tried with and without this
}
}
override func prepareForReuse() {
super.prepareForReuse()
// even though Apple recommends not to clean up ui elements in here, I still tried it to no success
priceLabel.text = ""
priceLabel.layoutIfNeeded() // tried with and without this
self.layoutIfNeeded() // tried with and without this
// I also tried removing the label with and without the 3 lines above
for view in self.subviews {
if view.isKind(of: UILabel.self) {
view.removeFromSuperview()
}
}
}
func cleanUpElements() {
priceLabel.text = ""
imageView.image = nil
}
}
I added 1 breakpoint for everywhere I added priceLabel.text = "" (3 total) and once the collectionView reloads the break points always get hit 6 times (3 times for the 2 objects in the datasource).The 1st time in prepareForReuse, the 2nd time in cellForItem, and the 3rd time in cleanUpElements()
Turns out I had to reset a property inside the cell. Even though the cells were being reused and the priceLabel.text was getting cleared, the property was still maintaining it's old bool value. Once I reset it via cellForItem the problem went away.
10 hrs for that, smh
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: customCell, for: indexPath) as! CustomCell
cell.someBoolProperty = false
cell.priceLabel.text = ""
cell.cleanUpElements()
cell.myModel = dataSource[indexPath.item]
return cell
}
In my swift app I have a UITableView with one static cell and many dynamic cells.
Static cell contains different fields, such as labels, map (taken from MapKit) and a button, that indicates whether user voted up or not.
Now, when user presses the button, I want to change its color, possibly without refreshing anything else.
So far my code looks like this:
var currentUserVote:Int = 0
func tableView(_ tview: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
if (indexPath as NSIndexPath).row == 0 {
let cell = tview.dequeueReusableCell(withIdentifier: "cellStatic") as! VideoDetailsCell
fetchScore(cell.score)
let voteUpImage = UIImage(named: "voteUp");
let tintedVoteUpImage = voteUpImage?.withRenderingMode(UIImageRenderingMode.alwaysTemplate)
cell.voteUpButton.setImage(tintedVoteUpImage, for: UIControlState())
checkUsersVote() { responseObject in
if(responseObject == 1) {
cell.voteUpButton.tintColor = orangeColor
} else if (responseObject == -1){
cell.voteUpButton.tintColor = greyColor
} else {
cell.voteUpButton.tintColor = greyColor
}
self.currentUserVote = responseObject
}
//map handling:
let regionRadius: CLLocationDistance = 1000
let initialLocation = CLLocation(latitude: latitude, longitude: longitude)
centerMapOnLocation(initialLocation, map: cell.mapView, radius: regionRadius)
//cell.mapView.isScrollEnabled = false
cell.mapView.delegate = self
.
.
.
return cell
} else {
//handle dynamic cells
}
}
So in the method above I'm checking if user voted already and based on that I'm setting different color on the button. I'm also centering the map on a specific point.
Now, since it's a static cell, I connected IBAction outlet to that button:
#IBAction func voteUpButtonAction(_ sender: AnyObject) {
if(currentUserVote == 1) {
self.vote(0)
}else if (currentUserVote == -1){
self.vote(1)
} else {
self.vote(1)
}
}
and the vote method works as follows:
func vote(_ vote: Int){
let indexPath = IndexPath(row: 0, section: 0)
let cell = tview.dequeueReusableCell(withIdentifier: "cellStatic") as! VideoDetailsCell
switch(vote) {
case 1:
cell.voteUpButton.tintColor = orangeColor
case 0:
cell.voteUpButton.tintColor = greyColor
case -1:
cell.voteUpButton.tintColor = greyColor
default:
cell.voteUpButton.tintColor = greyColor
}
tview.beginUpdates()
tview.reloadRows(at: [indexPath], with: .automatic)
tview.endUpdates()
currentUserVote = vote
//sending vote to my backend
}
My problem is, that when user taps the button, he invokes the method vote, then - based on the vote, the button changes color, but immediately after that method cellForRow is called and it changes the color of the button again. Also, it refreshes the map that's inside of it.
What I want to achieve is that when user taps the button, it should immediately change its color and that's it. Map stays untouched and the button is not changed again from cellForRow.
Is there a way of refreshing only that particular button without calling again cellForRow?
First of all, you confuse static and dynamic cells. You can use static cells only in the UITableViewController and you can't use static and dynamic cell at the same time.
I strongly recommend you not to use cell for storing map and button. All elements from the cell will be released after scrolling it beyond the screen.
I can advise you use TableViewHeaderView for this task. In this case you will be able set button and map view as #IBOutlet.
(See more about adding tableview headerView. You can also set it from interface builder.)
Another way is change tableView.contentInset and set your view with map and button as subview to tableView. This method is used when you need create Stretchy Headers.
It should be quite easy, simply do it in your button handler. The sender argument there is the button object that caused the action. When you were connecting it from IB there was a dropdown to select sender type, you may have missed it and the whole thing would have been obvious with UIButton type there.
Simply change your handler like this :
#IBAction func voteUpButtonAction(_ sender: UIButton) {
if(currentUserVote == 1) {
self.vote(0)
}else if (currentUserVote == -1){
self.vote(1)
} else {
self.vote(1)
}
sender.backgroundColor = yourFavouriteColor
}
Another approach would be to create an IBOutlet for your button, since its from a static cell, and then you would be able to reference it from any place in your view controller.
In this call:
func tableView(_ tview: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell
I see it calls checkUsersVote() which I'm guessing should get the updated value set in the vote() call. Could the problem be that you aren't doing this
currentUserVote = vote
until after reloadRows() is called?
I know this question has been asked many times.
I'm using a UICollectionView with custom cells which have a few properties, most important being an array of UISwitch's and and array of UILabel's. As you can guess, when I scroll, the labels overlap and the switches change state. I have implemented the method of UICollectionViewCell prepareForReuse in which I empty these arrays and reset the main label text.
I have tried to combine solutions from different answers and I have reached a point where my labels are preserved, but the state of my switches in the cells isn't. My next step was to create an array to preserve the state before removing the switches and then set the on property of a newly created switch to a value of this array at an index. This works, until after I scroll very fast and switches in cells which were not selected previously become selected(or unselected). This is creating a huge problem for me.
This is my collectionView cellForItemAtIndexPath method:
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier("pitanjeCell", forIndexPath: indexPath) as! PitanjeCell
// remove views previously created and create array to preserve the state of switches
var selectedSwitches: [Bool] = []
for item: UIView in cell.contentView.subviews {
if (item.isKindOfClass(UILabel) && !item.isEqual(cell.tekstPitanjaLabel)){
item.removeFromSuperview()
}
if (item.isKindOfClass(UISwitch)){
selectedSwitches.append((item as! UISwitch).on)
item.removeFromSuperview()
}
}
// get relevant data needed to place cells programmatically
cell.tekstPitanjaLabel.text = _pitanja[indexPath.row].getText()
let numberOfLines: CGFloat = CGFloat(cell.tekstPitanjaLabel.numberOfLines)
cell.setOdgovori(_pitanja[indexPath.row].getOdgovori() as! [Odgovor])
var currIndex: CGFloat = 1
let floatCount: CGFloat = CGFloat(_pitanja.count)
let switchConstant: CGFloat = 0.8
let switchWidth: CGFloat = cell.frame.size.width * 0.18
let heightConstant: CGFloat = (cell.frame.size.height / (floatCount + 2) + (numberOfLines * 4))
let labelWidth: CGFloat = cell.frame.size.width * 0.9
for item in _pitanja[indexPath.row].getOdgovori() {
// create a switch
let odgovorSwitch: UISwitch = UISwitch(frame: CGRectMake((self.view.frame.size.width - (switchWidth * 2)), currIndex * heightConstant , switchWidth, 10))
odgovorSwitch.transform = CGAffineTransformMakeScale(switchConstant, switchConstant)
let switchValue: Bool = selectedSwitches.count > 0 ? selectedSwitches[Int(currIndex) - 1] : false
odgovorSwitch.setOn(switchValue, animated: false)
// cast current item to relevant class
let obj: Odgovor = item as! Odgovor
// create a label
let odgovorLabel: UILabel = UILabel(frame: CGRectMake((self.view.frame.size.width / 12), currIndex * heightConstant , labelWidth, 20))
odgovorLabel.text = obj.getText();
odgovorLabel.lineBreakMode = NSLineBreakMode.ByWordWrapping
odgovorLabel.font = UIFont(name: (odgovorLabel.font?.fontName)!, size: 15)
// add to cell
cell.addSwitch(odgovorSwitch)
cell.addLabel(odgovorLabel)
currIndex++
}
return cell
}
My custom cell also implements methods addSwitch and addLabel which add the element to the contentView as a subview.
Is there any way I can consistently preserve the state of switches when scrolling?
EDIT: As per #Victor Sigler suggestion, I created a bydimensional array like this:
var _switchStates: [[Bool]]!
I initialized it like this:
let odgovori: Int = _pitanja[0].getOdgovori().count
_switchStates = [[Bool]](count: _pitanja.count, repeatedValue: [Bool](count: odgovori, repeatedValue: false))
And I changed my method like this:
for item: UIView in cell.contentView.subviews {
if (item.isKindOfClass(UILabel) && !item.isEqual(cell.tekstPitanjaLabel)){
item.removeFromSuperview()
}
if (item.isKindOfClass(UISwitch)){
_switchStates[indexPath.row][current] = (item as! UISwitch).on
current++
selectedSwitches.append((item as! UISwitch).on)
item.removeFromSuperview()
}
}
And in the end:
let switchValue: Bool = _switchStates.count > 0 ? _switchStates[indexPath.row][Int(currIndex) - 1] : false
First of all as you said in your question regarding the default behavior of the cell in the UICollectionView you need to save the state of each cell, in your case with the UISwitch, but you need to preserve the state in a local property, not in the cellForRowAtIndexPath method because this method is calles every time a cell is going to be reused.
So first declare the array where you going to save the state of the UISwitch's outside this function, something like this:
var selectedSwitches: [Bool] = []
Or you can declare it and then in your viewDidLoad instantiate it, it's up to you, I recommend you instantiate it in your viewDidLoad and only declare it as a property like this:
var selectedSwitches: [Bool]!
Then you can do whatever you want with the state of your UISwitch's always of course preserving when change to on or off.
I hope this help you.
I have done it!
In the end I implemented this:
func collectionView(collectionView: UICollectionView, didEndDisplayingCell cell: UICollectionViewCell, forItemAtIndexPath indexPath: NSIndexPath) {
var current: Int = 0
var cell = cell as! PitanjeCell
for item: UISwitch in cell.getOdgovoriButtons() {
if(current == _switchStates[0].count) { break;}
_switchStates[indexPath.row][current] = (item).on
current++
}
}
In this function I saved the state.
This in combo with prepareForReuse:
public override func prepareForReuse() {
self.tekstPitanjaLabel.text = nil
self._odgovoriButtons.removeAll()
self._odgovoriLabels.removeAll()
self._odgovori.removeAll()
super.prepareForReuse()
}
Finally did it!
I am building a tvos application. i have a strange bug where UICollectionView lose focus of the previously selected cell when i navigate back to that particular view. The scenario is some thing this like this.
I have two UIViewControllers A and B. A has a UITableView and it has three prototype cells in it. Each cell has a horizontal scrolling UICollectionView inside it. When i click on any of UICollectionViewCell it navigates to the B (detail page). I am presenting B modally.
Now when i press Menu button on Siri remote view A appears again (in other words view B is removed from View hierarchy) but the current selected cell is different then the previously selected. I have tried to use remembersLastFocusedIndexPath with both true and false values and also tried by implementing
func indexPathForPreferredFocusedViewInCollectionView(collectionView: UICollectionView) -> NSIndexPath?
but the control neves comes to this function when i navigate back to view A. I am also reloading every thing in viewWillAppear function.
Can any one help me in this. Thanks
The property remembersLastFocusedIndexPath should be set to true for the collectionView and false for the tableView.
Also, Are you reloading the UITableView in viewWillAppear i.e Is the table data being refreshed when the B is popped and A appears?
If Yes, then lastFocusedIndexPath will be nil on reload.
We faced the same issue. We solved it by not reloading the contents when B is popped.
Maintain a flag say didPush. Set this flag to true when B is pushed. When A appears check whether the flag is set and only then fetch data and reload table.
This worked for us.
I don't remember exactly, but I know there was a known issue for remembersLastFocusedIndexPath where it wasn't working as intended.
This is one workaround, although take it with a grand of salt as it does seem slightly hacky and it uses the common (but potentially unstable) approach of overriding the preferredFocusedView property.
private var viewToFocus: UIView?
override var preferredFocusView: UIView? {
get {
return self.viewToFocus
}
}
Save locally the indexPath of the last cell in View A when presenting View B
// [1] Saving and scrolling to the correct indexPath:
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
...
collectionView.scrollToItemAtIndexPath(indexPath:, atScrollPosition:, animated:)
}
// [2] Create a dispatchTime using GCD before setting the cell at indexPath as the preferredFocusView:
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(animated)
...
let dispatchTime: dispatch_time_t = dispatch_time(DISPATCH_TIME_NOW, Int64(CGFloat.min * CGFloat(NSEC_PER_SEC)))
dispatch_after(dispatchTime, dispatch_get_main_queue(), {
self.viewToFocus = collectionView.cellForItemAtIndexPath(indexPath:)
// [3] Request an update
self.setNeedsFocusUpdate()
// [4] Force a focus update
self.updateFocusIfNeeded()
}
}
The reason we split the two methods into both viewWillAppear and viewDidAppear is that it eliminates a bit of the animation jump. If anyone else could jump in with suggestions to improve or even alternate solutions, I'd also be interested!
In Swift
If you want to focus collection view Cell then
You can use collectionview Delegate method, method name is
func collectionView(collectionView: UICollectionView, didUpdateFocusInContext context: UICollectionViewFocusUpdateContext, withAnimationCoordinator coordinator: UIFocusAnimationCoordinator)
{
}
You can use this method like this...
func collectionView(collectionView: UICollectionView, didUpdateFocusInContext context: UICollectionViewFocusUpdateContext, withAnimationCoordinator coordinator: UIFocusAnimationCoordinator) {
if let previousIndexPath = context.previouslyFocusedIndexPath,
let cell = collectionView.cellForItemAtIndexPath(previousIndexPath) {
cell.contentView.layer.borderWidth = 0.0
cell.contentView.layer.shadowRadius = 0.0
cell.contentView.layer.shadowOpacity = 0
}
if let indexPath = context.nextFocusedIndexPath,
let cell = collectionView.cellForItemAtIndexPath(indexPath) {
cell.contentView.layer.borderWidth = 8.0
cell.contentView.layer.borderColor = UIColor.blackColor().CGColor
cell.contentView.layer.shadowColor = UIColor.blackColor().CGColor
cell.contentView.layer.shadowRadius = 10.0
cell.contentView.layer.shadowOpacity = 0.9
cell.contentView.layer.shadowOffset = CGSize(width: 0, height: 0)
collectionView.scrollToItemAtIndexPath(indexPath, atScrollPosition: [.CenteredHorizontally, .CenteredVertically], animated: true)
}
}
In my cellForRowAtIndexPath method I set the cornerRadius of the layer on my image:
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("feedCell")!
if self.pictunes?.count > 0 {
// There are some pictunes to show; Create and update the posts
if self.pictuneImages.count > indexPath.row {
// We have an image for the user who made the current pictune
if let pictunerImageView = cell.contentView.viewWithTag(2) as? UIImageView {
pictunerImageView.layer.cornerRadius = 17.5 // Cut it to a circle
pictunerImageView.image = self.pictunerImages[0]
}
// We also have an image for the pictune at the current post
if let pictuneImageView = cell.contentView.viewWithTag(1) as? UIImageView {
pictuneImageView.image = self.pictuneImages[indexPath.row]
}
}
return cell
} else {
// No pictunes have loaded yet; We probably need more time
// to load the image and audio assets for some of them
cell.textLabel!.text = "No Pictunes Available Yet"
return cell
}
}
But when I scroll I see this nasty background effect:
How should I get rid of this effect? Clearing the background context didn't help at all. Thanks!
Set:
pictunerImageView.layer.masksToBounds = true
after:
pictunerImageView.layer.cornerRadius = 17.5
You could also change this to:
pictunerImageView.layer.cornerRadius = pictunerImageView.frame.size.height *0.5
In case you ever want to change the size but still want it to be a circle.