I'm trying to implement a tableView that has 4 different possible prototype cells. They all inherit from base UITableViewCell class and implement its protocol.
For two of the cells there's asynchronous data fetching but one in particular has been giving me fits. The flow is as follows:
1) Dequeue reusable cell
2) Call configure
func configure(someArguments: ) {
//some checks
process(withArguments: ) { [weak self in] in
if let weakSelf = self {
weakSelf.reloadDelegate.reload(forID: id)
}
}
}
3) If the async data is in the cache, configure the cell using the image/data/stuff available and be happy
4) If the async data is NOT in the cache, fetch it, cache it, and call the completion
func process(withArguments: completion:) {
if let async_data = cache.exists(forID: async_data.id) {
//set labels, add views, etc
} else {
fetch_async_data() {
//add to cache
//call completion
}
}
}
5) If the completion is called, reload the row in question by passing the index path up to the UITableViewController and calling reloadRows(at:with:)
func reload(forID: ) {
tableView.beginUpdates()
tableView.reloadRows(at: indexPath_matching_forID with: .automatic)
tableView.endUpdates()
}
Now, my understanding is that reloadRows(at:with:) will trigger another dataSource/delegate cycle and thus result in a fresh resuable cell being dequeued, and the configure method being called again, thereby making step #3 happy (the async data will now be in the cache since we just fetched it).
Except...that's not always happening. If there are cells in my initial fetch that require reloading, it works - they get the data and display it. Sometimes, though, scrolling down to another cell that requires fetching DOES NOT get the right data...or more specifically, it doesn't trigger a reload that populates the cell with the right data. I CAN see the cache being updated with the fresh data, but it's not...showing up.
If, however, I scroll completely past the bad cell, and then scroll back up, the correct data is used. So, what the hell reloadRows?!
I've tried wrapping various things in DispatchQueue.main.async to no avail.
reloadData works, ish, but is expensive because of potentially many async requests firing on a full reload (plus it causes some excessive flickering as cells come back)
Any help would be appreciated!
Reused cells are not "fresh". Clear the cell while waiting for content.
func process(withArguments: completion:) {
if let async_data = cache.exists(forID: async_data.id) {
//set labels, add views, etc
} else {
fetch_async_data() {
// ** reset the content of the cell, clear labels etc **
//add to cache
//call completion
}
}
}
Related
I have a horizontal scrolling collection view inside a UITableView cell, achieving the view same as that of Netflix.
Currently, I am loading URL data in my view controller containing table view and passing the array of data in UITableViewCell which contains the collectionView, and then rendering collection view cells.
But I'm feeling lack of controls using this method. For e.g, UI management, hiding, showing views depending on URL data load and error, etc.
I tried loading URL data inside table view cell and that works
perfectly fine for me but I don't think that's appropriate to do, as
only controllers should control everything.
The closure I'm using to load data in my controller is -
private func fetchData() {
let id = UserDefaults.standard.getUserId()
Service.shared.fetch(userId: id) { (data, error) in
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.5, execute: {
guard error == nil else {
print(error?.localizedDescription ?? "Error")
return
}
let result = data?.count != 0 ? "Success" : "Failure"
switch result {
case ResultType.Failure.rawValue:
print("Failure")
case ResultType.Success.rawValue:
if let data = data {
self.data = data
}
default: break
}
})
}
}
Back to the Question, Is it fine loading the data inside
UITableViewCell in order to hide/show or animate UICollectionView inside that UITableViewCell?
Moreover, Assume a scenario where I have to load 4-5 URL data and render them in each custom table view cell which may or may not contain a collection view.
Complicated!
You can load data in a view, but it wouldn’t be a good architecture. It hampers reusabilty and mixes responsibilities. Also, table view cells will be reused, which will eventually lead to weird data loading behavior and probably bugs.
I suggest extracting data loading into a custom class, and using that class in the view controller. This way your data loading is decoupled from the controller and the view, giving the most flexibility.
I searched a lot through Google and SO, so please forgive me, if this question has already been answered!
The problem:
I have a UICollectionView with n UICollectionViewCells. Each cell contains a UIView from a XIB file. The Views are used for data entry, so all cells have a unique reuseIdentifier. Each View has also a unique restorationIdentifier. Everything works in normal usage, but not when it comes to state restoration:
The first 3 or 4 cells are getting restored properly because they are visible on the screen on startup, but the remaining cells, which are not visble, are not getting restored.
Current solution:
So I've discovered so far that a View is only restored if it's added to userinterface at startup.
My current working solution is to set the height of all cells to 1 in the process of restoring. Now every cell is loaded and all views are restored.
When applicationFinishedRestoringState() is called, I reload the CollectionView with the correct height.
Now my question is: I'm not happy with this solution, is there a more clean way to achieve restoring of all the UIViews?
I think you are getting a bit confused between your data model and your views. When first initialised, your table view is constructed from a data model, pulling in stored values in order to populate whatever is in each cell. However, your user does not interact directly with the data model, but with the view on the screen. If the user changes something in the table view, you need to signal that change back up to the view controller so that it can record the change to the data model. This means in turn that if the view needs to be recreated the view controller has the information it needs to rebuild whatever was in the table when your app entered the background.
I have put together a simple gitHub repository here: https://github.com/mpj-chandler/StateManagementDemo
This comprises a CustomTableViewController class which manages a standard UITableView populated with CustomTableViewCells. The custom cells contain three switch buttons, allowing the state of each cell to be represented by an array of Boolean values.
I created a delegate protocol for the cells such that if any of the switches is tripped, a signal is sent back to the view controller:
protocol CustomTableViewCellDelegate {
func stateDidChange(sender: CustomTableViewCell) -> Void
}
// Code in CustomTableViewCell.swift:
#objc fileprivate func switched(sender: UISwitch) -> Void {
guard let index : Int = switches.index(of: sender) else { return }
state[index] = sender.isOn
}
// The cell's state is an observed parameter with the following didSet method:
fileprivate var state : [Bool] = Array(repeating: false, count: 3) {
didSet {
if state != oldValue, let _ = delegate {
delegate!.stateDidChange(sender: self)
}
}
}
CustomTableViewController is registered to the CustomTableViewCellDelegate protocol, so that it can record the change in the model as follows:
// Code in CustomTableViewController.swift
//# MARK:- CustomTableViewCellDelegate methods
internal func stateDidChange(sender: CustomTableViewCell) -> Void {
guard let indexPath : IndexPath = tableView.indexPath(for: sender) else { return }
guard indexPath.row < model.count else { print("Error in \(#function) - cell index larger than model size!") ; return }
print("CHANGING MODEL ROW [\(indexPath.row)] TO: \(sender.getState())")
model[indexPath.row] = sender.getState()
}
You can see here that the function is set up to output model changes to the console.
If you run the project in simulator and exit to the home screen and go back again you will see the state of the tableView cells is preserved, because the model reflects the changes that were made before the app entered the background.
Hope that helps.
I'm looking for any possible way of passing the result of an networking update to a button in a UITableViewCell as a closure.
I have some UITableViewCells that are products. In these cells, I have an 'Add to Cart' button. I set a buttonTap closure in my UITableViewCell cellforRowAtIndexPath method, setup a touch handler within the cell for the button, and when that handler is called, execute the buttonTap closure. I handle my cart updating on a cart object which lives on the main controller.
The result of the cart update action returns true if they can add more items to their cart. Then, I update the button accordingly. I like this approach because I don't have to deal with delegates and I can keep all of the cart logic itself far far away from the cell; the cell just knows how to make a button enabled/disabled/loading/etc.
/// Buttom tap callback callback.
public typealias Selection = () -> Bool
class MealTableViewCell: UITableViewCell {
var buttonTap: Selection?
// Runs when tapping the button
func didTapAdd() {
if let buttonBlock = buttonTap {
self.button.isLoading = true
// Simulate loading
DispatchQueue.main.asyncAfter(deadline: .now() + 0.4) {
self.button.enabled = buttonBlock()
self.button.isLoading = false
}
}
}
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = .... (fetch cell)
cell.buttonTap = {
// returns true if the user can add more items to their cart
return self.cart.update(product: product, quantity: 1)
}
}
My question is that currently, my cart is all local with no API calls. I'm currently switching the cart over to an API driven one, with network calls to add and remove items. That means I can no longer return a BOOL, or return at all, from my cart.update(product:,quantity:) method as it is now an async call.
So, I can do something like rewrite that method signature to be
self.cart.update(product: product, quantity: 1, success: { canAddMore in
// API call succeeded
}, failure: { error in
// fall failed
})
The question is that how can I pass canAddMore to the tableViewCell? If I redefine what Selection means to take in a block that takes a bool as a param, I can't pass that param in from the controller as it would only be passed in when the block is executed on the cell itself.
How can I do something like
cell.buttonTap = {
cell.buttonTap = {
self.cart.update(product: product, quantity: 1), success: { canAddMore in
// !!!! What can I call here to pass canAddMore to the cell.
}, failure: { error in
}
}
}
canAddMore can be any value really, a BOOL is just this example. My big goal is to avoid coupling any knowledge of the cell's loading and buttons to the controller itself. If I use delegates, I would have to have a two way delegate makes the cell a delegate of the controller, and I've always felt that's the sort of wrong direction to approach this. I'm not positive it's really possible to pass the result of a closure back to the cell, but I am hoping there is!
EDIT: The big question I'm really trying to answer is if it is at all possible to pass data back to the cell (or any object) that originally called closure through that closure. There's a million ways to do data modifications in a table view, but that's sort of the main thing I'm trying to address.
I'm also "looking" to avoid storing the canAddMore state (e.g. the quantity remaining for that product) in the main 'products' array that powers the tableview. The initial state is set there, returned from a /products endpoint, but after that, inventory being available or not is returned by the carts API action.
I don't think you want to do what you think you want to do :)
In a nutshell, instead of trying to "talk back" to the cell that called the closure, you probably want to track the "canAddMore" state of each product in your Products data array, and then update the table row(s) when the state changes. So...
User taps "Add to Cart"
Give visual feedback in that row to show that you are processing the tap (gray out the button, or show a spinner, whatever looks good)
Call back to the closure to start the Add-to-cart API call
When the API call returns, update your local Products data to indicate the "canAddMore" state
reload the row(s) in the table to update the Button (make it active, inactive, change the title, whatever)
You almost certainly need to be doing something similar anyway, so the Buttons in each row will be updated when the user scrolls and the cells are reused.
A general approach is to update the cell's content with tableView.reloadRows(at: [indexPath], with: true) in your callback. This will call func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell for the specified cell. Don't forget that this has to be done in the main queue.
I have a tableView inside a collectionViewCell and I get an error when I try to reload the data.
*** Assertion failure in -[UITableView _endCellAnimationsWithContext:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3600.6.21/UITableView.m:1610
I tried using Dispatch.main.async and it seems to get rid of the problem. The only thing is that it doesn't reload the data and nothing changes in the tableView
func cleanItems(completion: #escaping (Bool) -> Void) {
Dispatch.main.async {
cell.tableView.beginUpdates()
// Make changes in the Data Source
cell.tableView.deleteRows(at: selectedItems, with: .fade)
cell.tableView.endUpdates()
// Reloading sections accordingly depending on what the user has deleted
// Do I need to reload data here again? It used to work without Dispatch, but it wasn't stable
cell.tableView.reloadData()
// Updating items with if statements to reload data in Firebase
completion(true)
}
}
This doesn't reload the data at all and nothing seems to change. The good thing is that I don't get a random crash, which was the case before implementing Dispatch.main.async
I've retrieved the numberOfRows in each section to see how many rows there are after ending updates.
print(cell.tableView.numberOfRows(inSection: 1))
and I get the same number of rows that are in the current view.
This is crucial, because if the tableView sections are all zero, the collectionViewCell should disappear. And we never get here in the completion block as it says that the numberOfRows has never changed. Leaving us with a non updated tableView.
I solved this by moving Dispatch.main.async outside the function call.
Dispatch.main.async {
cleanItems(completion: { (success) in
etc.
})
}
I added 2 UIButton in my custom UITableViewCell.
When pressed something is done with the displayed object(in this case a User). Now I want the row/cell to disappear. My Idea was to reload the screen via triggering the viewDidLoad() and viewDidAppear() functions,
since i use PFQueries to obtain user data and display them in my table view.
What happens is, that other than deleting that row since my query shouldn't find the data, it just adds the same things again.
Is there a better way to solve this? I want to delete the row and redo my Query.
To delete a row from a table, you can use a function like this:
// Add this function to your ViewController
func tableDeleteRow(indexPath: NSIndexPath) {
// IMPLEMENT ME:
// first, remove the item from the data that drives the tableView.
// This is what I do. Yours will be different.
// self.tableData.removeAtIndex(indexPath.row)
// tell the table to delete the row
dispatch_async(dispatch_get_main_queue()) {
// Code
print("remove from table")
self.tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
}
}
If you are looking to reload the entire table and redo the data you got from the server, do this:
// This is pseudo code.
func tableRefresh() {
// this is a pseudo code function.
// replace it with your own.
get_data_from_server() {
(data, response, error) in
// do something with data
dispatch_async(dispatch_get_main_queue()) {
print("refresh table")
self.tableView.reloadData()
}
}
}