Let's say I am making scrollable pages with a UICollectionView. The pages are all different and are populated by a pages array like the one below:
let pages = [GreenPage(), YellowPage(), OrangePage(), YellowPage(), GreenPage()]
So, to clarify, there would be a page that's green, then followed by yellow, then orange ...
Now, let's say I want to make it so that when one is tapped, it runs a function called tapped() which occurs in each GreenPage(), YellowPage(), and OrangePage().
Now, the only way I see to do this would be the following:
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
if let greenPage = collectionView.cellForItem(at: indexPath) as! GreenPage {
greenPage.tapped()
} else if let yellowPage = collectionView.cellForItem(at: indexPath) as! YellowPage {
yellowPage.tapped()
} else if let orangePage = collectionView.cellForItem(at: indexPath) as! OrangePage {
orangePage.tapped()
}
}
This seems super redundant. Is there another way to do this assuming the tapped function for each class does the same thing?
This is a good example for a protocol. Create it
protocol Tappable {
func tapped()
}
adopt the protocol
class GreenPage : Tappable { ...
class YellowPage : Tappable { ...
class OrangePage : Tappable { ...
This reduces the code in didSelectItemAt considerably
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
(collectionView.cellForItem(at: indexPath) as? Tappable)?.tapped()
}
This is a great time to use protocols. If they all conform to a protocol that has tapped() as a requirement. You then say the array of pages is an array of tour protocol with this:
let pages: [YourProtocol] = [...]
It then your usage be getting the cell and calling tapped()
For more on protocols read this
Also sorry for formatting, I’m on my phone.
Related
I need to store a view to use as a UICollectionView header. I don't want it to cycle out of memory though, because it needs to keep its state/data, etc.
With a table view you can just do tableView.tableHeaderView = view.
Here's what I'm trying:
func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
switch kind {
case MagazineLayout.SupplementaryViewKind.sectionHeader:
if let t = headerView { //headerView is an instance var
return t
} else {
let view = collectionView.dequeueReusableSupplementaryView(ofKind: MagazineLayout.SupplementaryViewKind.sectionHeader, withReuseIdentifier: "MyHeaderView", for: indexPath) as! MyHeaderView
view.titleLabel.text = "test"
view.switch.addAction(for: .valueChanged, { [weak self] in
self?.switchValueChanged()
})
headerView = view
return view
}
...
}
I don't want to re-create it every time the user scrolls it away and then back, so I'm trying to store a reference to it. This isn't working though. Hard to explain but the view it displays is cut off and the switch isn't responsive. If I comment out the "if" part and just create a new one every time, it looks correct but state is lost (i.e. the switch gets turned off) What's the best way to do this?
Since you're keeping the reference and not letting it deallocate when it scrolls out of the view, remove the register and dequeuing entirely. It worked fine for me, here's how:
let view = MyHeaderView()
override func viewDidLoad() {
super.viewDidLoad()
view.titleLabel.text = "test"
view.switch.addAction(for: .valueChanged, { [weak self] in
self?.switchValueChanged()
})
}
func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
switch kind {
case MagazineLayout.SupplementaryViewKind.sectionHeader:
return view
//...
}
}
Using protocol / delegate & retrieve the data from didSelectItemAt (collectionViews).
// This class have the data
// WhereDataIs: UICollectionViewController
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
//Pass some data from the didSelect to a delegate
let test = things[indexPath.item]
guard let bingo = test.aThing else { return }
print("bingo: ", bingo)
That bingo is printing the value that I need. So pretty good right there.
Now, I can't use the method of the protocol inside of that function, that's bad execution so the compiler or Xcode says hey, you will declare the method as a regular method, not the nested way.
//Bridge
protocol xDelegate {
func x(for headerCell: HeaderCell)
}
//This is the class that need the data
//class HeaderCell: UICollectionViewCell
var xDelegate: xDelegate?
//it's init()
override init(frame: CGRect) {
super.init(frame: frame)
let sally = WhereDataIs()
self.xDelegate = sally
xDelegate?.x(for: self)
}
// This extension is added at the end of the class WhereDataIs()
// Inside of this class is it's delegate.
var xDelegate: xDelegate? = nil
extension WhereDataIs: xDelegate {
func x(for headerCell: HeaderCell) {
//Smith value will work because it's dummy
headerCell.lbl.text = "Smith"
// What I really need is instead of "Smith" is the value of didselectItemAt called bingo.
headerCell.lbl.text = bingo
}
}
Hat's off for anyone who would like to guide me in this.
Not using delegates, but it will work
Solved by:
1) go to the controller of the collectionView. make a new variable to store the items.
// Pass the item object into the xController so that it can be accessed later.
//(didSelectItemAt)
xController.newVar = item
//xController class: UICollectionView...
// MARK: - Properties
var newVar: Thing?
Finally in that class, you should have the the method viewForSupplementaryElementOfKind in which you register the HeaderCell and then just add...
let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: headerId, for: indexPath) as! HeaderCell
header.lbl.text = newVar.whatEverYourDataIs
Little generic but it works. :)
I think you can just add this to the end of your current code in didSelectItemAt indexPath:
guard let header = collectionView.supplementaryView(forElementKind: "yourElementKind", at: indexPath) as? HeaderCell else { return }
header.lbl.text = bingo
collectionView.reloadData()
Edit: Keep everything else for now to ensure you get a good result first.
Let me know if this works, happy to check back.
I have an app which has two tabs. In the first BookVC tab, I use UICollectionViewController to show books and in didSelectItemAtIndexPath i call a function that push the BookDetailVC.
And in Bookmark tab, i want to show all books which was bookmarked and when user select certain book, i want to push BookDetailVC. I know it can be achieved by writing the same code as in BookVC. But i don't want to repeat the same code.
I'd tried to make BookmarkVC subclass of BookVC and ended up as showing the same book in both BookVC and BookmarkVC since i'm using the same one instance of UICollectionView from BookVC. Is there any way to override UICollectionView of BookVC or any other approach to solve. Sorry for my bad english. Thanks.
You are taking the wrong approach. The way you describe your bookmarks and your books View controller, it seems to me that they are identical, the only thing that changes is the content.
So, since collection views use data sources all you have to do is change the Data source based on whether you wanna show all books, or only the bookmarked ones.
Added code:
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let viewController = storyboard.instantiateViewController(withIdentifier :"secondViewController") as! UIViewController
self.present(viewController, animated: true)
I think you are doing wrong use just need to reload collection view based on which button is clicked take boolean
isBookMarkCliked:Bool
For Better Readablity create Model For Book
like
class Book {
var title: String
var author: String
var isBookMarked:Bool
init(title: String, author: String, isBookMarked:Bool) {
self.title = title
self.author = author
self.isBookMarked = isBookMarked
}
}
and declare two array globally with Book Model
arrForBooks:[Book] = []
arrForBookMarkedBooks:[Book] = []
Create CollectionViewDelegate methods using extension
extension YourClassVC: UICollectionViewDataSource,UICollectionViewDelegate
{
//MARK: UICollectionViewDataSource
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
{
if isBookMarkClicked
{
return arrForBookMarkedBooks.count
}
return arrForBooks.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
{
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CellIdentifier", for: indexPath) as! YourCellClass
var currentBook:Book = nil
if isBookMarkClicked
currentBook = arrForStoreDetails[indexPath.row]
else
currentBook = arrForBookMarkedBooks[indexPath.row]
//Set data to cell from currentBook
return cell
}
//MARK: UICollectionViewDelegateFlowLayout
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
collectionView.deselectItem(at: indexPath, animated: false)
//Your code to push BookDetailVC
}
}
I'm following a tutorial for making an Instagram-esque app, and the tutorial goes through how to display all data (image, author, likes, etc) all in one collection view. I'm trying to do it a little bit differently so only the images are displayed in the collection view, then if an image is tapped, the user is taken to a different view controller where the image plus all the other data is displayed.
So in my view controller with the collection view (FeedViewController), I have my array of posts declared outside the class (Post is the object with all the aforementioned data):
var posts = [Post]()
Then inside the FeedViewController class, my cellForItemAt indexPath looks like this:
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "postCell", for: indexPath) as! PostCell
// creating the cell
cell.postImage.downloadImage(from: posts[indexPath.row].pathToImage)
photoDetailController.authorNameLabel.text = posts[indexPath.row].author
photoDetailController.likeLabel.text = "\(posts[indexPath.row].likes!) Likes"
photoDetailController.photoDetailImageView.downloadImage(from: posts[indexPath.row].pathToImage)
return cell
}
And then I also obviously have a function to fetch the data which I can post if necessary, but I think the problem is because PhotoDetailController doesn't know the indexPath (although I may be wrong).
When I run the app and try to view the FeedViewController I get a crash fatal error: unexpectedly found nil while unwrapping an Optional value, highlighting photoDetailController.authorNameLabel line.
Am I correct in assuming the problem is because the indexPath is available only in the collection view data sources within FeedViewController? If so, how can I pass that indexPath to PhotoDetailController so my code works correctly?
Thanks for any advice!
EDIT: Edited my didSelectItem method:
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let photoDetailController = self.storyboard?.instantiateViewController(withIdentifier: "photoDetail") as! PhotoDetailController
photoDetailController.selectedPost = posts[indexPath.row]
self.navigationController?.pushViewController(photoDetailController, animated: true)
}
and cellForItemAt:
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "postCell", for: indexPath) as! PostCell
cell.postImage.downloadImage(from: posts[indexPath.row].pathToImage)
return cell
}
And in PhotoDetailController:
var selectedPost: Post! inside the class, then:
override func viewDidLoad() {
super.viewDidLoad()
self.authorNameLabel.text = selectedPost[indexPath.row].author
self.likeLabel.text = "\(selectedPost[indexPath.row].likes!) Likes"
self.photoDetailImageView.downloadImage(from: selectedPost[indexPath.row].pathToImage)
}
But still getting error use of unresolved identifier "indexPath
EDIT 2: Storyboard
You are getting this nil crash because this photoDetailController is not yet loaded so all its outlet are nil also the way currently you are doing is also wrong.
You need to add the controller code in didSelectItemAt method and perform the navigation.
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let photoDetailController = self.storyboard?.instantiateViewController(withIdentifier: "YourIdentifier") as! PhotoDetailController
photoDetailController.selectedPost = posts[indexPath.row]
self.navigationController?.pushViewController(photoDetailController, animated: true)
}
Now simply create one instance property of type Post with name selectedPost in PhotoDetailController and set all the detail from this selectedPost object in viewDidLoad of PhotoDetailController.
Edit: Set your viewDidLoad like this in PhotoDetailController
override func viewDidLoad() {
super.viewDidLoad()
self.authorNameLabel.text = selectedPost.author
self.likeLabel.text = "\(selectedPost.likes!) Likes"
self.photoDetailImageView.downloadImage(from: selectedPost.pathToImage)
}
I have a collection view that scrolls horizontally and each cell pushes to a detail view upon a tap. When I load the app, I have it print the object at index. At first it will load the one cell it is supposed to. But when I scroll over one space it prints off two new ids, and then begins to associate the data of the last loaded cell with the one currently on the screen, which is off by one spot now. I have no clue how to resolve this, my best guess is there is some way to better keep up with the current index or there is something in the viewDidAppear maybe I am missing. Here is some code:
open var currentIndex: Int {
guard (self.collectionView) != nil else { return 0 }
return Int()
}
public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ExpandCell", for: indexPath) as! ExpandingCollectionViewCell
let object = self.imageFilesArray[(indexPath).row] as! PFObject
cell.nameLabel.text = object["Name"] as! String
whatObject = String(describing: object.objectId)
print(whatObject)
return cell
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let object = self.imageFilesArray[(indexPath as NSIndexPath).row]
guard let cell = collectionView.cellForItem(at: indexPath) as? ExpandingCollectionViewCell else { return }
let storyBoard : UIStoryboard = UIStoryboard(name: "Main", bundle:nil)
let nextViewController = storyBoard.instantiateViewController(withIdentifier: "EventDetailViewController") as! EventDetailViewController
nextViewController.lblName = nameData
nextViewController.whatObj = self.whatObject
self.present(nextViewController, animated:false, completion:nil)
}
Does anyone know a better way to set the current index so I am always pushing the correct data to the next page?
The data source that is setting the elements of the cell can keep count of index that can also be set as a property and can be used to retrieve back from the cell to get correct current index.
EventDetailViewController is your UICollectionViewController subclass I assume.
If this is correct then you need to implement on it:
A method that tells the collection how many items there are in the datasource.
//1
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1 // you only have 1 section
}
//2
override func collectionView(_ collectionView: UICollectionView,
numberOfItemsInSection section: Int) -> Int {
return array.count// this is the number of models you have to display... they will all live in one section
}
A method that tells the collection which cellView subclass to use for that given row.
-A method that populates the cell with it's datasource.
Follow this tutorial from which I extracted part of the code, they convey this core concepts pretty clearly.
Reusing, as per Apple's docs happens for a number of cells decided by UIKit, when you scroll up a little bit 2 or N cells can be dequed for reusing.
In summary, with this three methods you can offset your collection into skipping the one record that you want to avoid.
Happy coding!