TableView CellReuse - ios

Question

I have problems with my custom cell file in tableview. I managed to get it done using the out comment line shown below, but the performance was really bad when it had 10+ cells.
UsingdequeueReusableCell leads to this error:
'NSInternalInconsistencyException', reason: 'unable to dequeue a cell with identifier DiveNewsShort - must register a nib or a class for the identifier or connect a prototype cell in a storyboard'
which is strange, because I do register the nib in viewDidLoad(). I hope you can help me, I am getting frustrated by this.
class ProfilTableView: UITableViewController {
override func viewDidLoad() {
super.viewDidLoad()
tableView.register(UINib(nibName: "DiveNewsShort", bundle: nil), forCellReuseIdentifier: "DiveNewsShort")
tableView.register(DiveNewsShort.self, forCellReuseIdentifier: "DiveNewsShort")
}
public override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
// let cell = Bundle.main.loadNibNamed("DiveNewsShort", owner: self, options: nil)?.first as! DiveNewsShort
// This one works as expected
let cell = tableView.dequeueReusableCell(withIdentifier: "DiveNewsShort", for: indexPath) as! DiveNewsShort
// This one does not
return cell }
Update:
I managed to get rid of the error by adding the register function in the cellForRowAt function, but I don't think that this is a efficient way actually. It should work within the vieDidLoad shouldn't it?
public override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
tableView.register(UINib(nibName: "DiveNewsShort", bundle: nil), forCellReuseIdentifier: "DiveNewsShort")
let cell = tableView.dequeueReusableCell(withIdentifier: "DiveNewsShort", for: indexPath) as! DiveNewsShort
return cell }

Answer 1

You don't need this line:
tableView.register(DiveNewsShort.self, forCellReuseIdentifier: "DiveNewsShort")
You already have registered the nib file one line before.

Answer 2

There are three ways to register cells for reuse/dequeuing:
You are programmatically creating the cells, in which case you register the class in viewDidLoad.
You are using a NIB, in which case you register the NIB in viewDidLoad.
You are using storyboard cell prototypes, in which case you don't have to register anything. The storyboard does all of this for you.
Since you are using NIBs, you should remove the registering of the class and only register the NIB. And you should do this in viewDidLoad. This process is outlined in https://stackoverflow.com/a/28490468/1271826 as well as in Reinier's answer.
Looking at your MCVE, your problem was a result of a more fundamental mistake, where you had a UIViewController trying to use another view controller, which was a UITableViewController, to manage the table. But UITableViewController has its own UITableView and won't use the one that you have an #IBOutlet for, so you were registering the NIB for a table view you weren't seeing. There were a ton of other issues here (e.g. if you really want a view controller within a view controller, you have to do view controller containment calls, etc.), but the simplest solution was to excise this separate UITableViewController from the project and when this was fixed, it works precisely as we described. See https://github.com/robertmryan/Divers for a working version of your MCVE.
You also didn't hook up the outlets for the other two controls in your cell (the switch and slider). Thus, if you changed either of those two controls and then scrolled, the cells are reused and you see the changed UIKit control that was done for some other cell, but was subsequently reused. To fix that, your custom UITableViewCell subclass should have outlets for all controls, and cellForRowAt must set values for all of these outlets. You also need some mechanism for the cell to inform the view controller when the switch and slider have changed and update the model accordingly, so when cellForRowAt was later called for that row, it would know the state of that CellData to set the control appropriately. A common solution for this is to use the protocol-delegate pattern. See the above GitHub repo, which illustrates this pattern, too.

Answer 3

I have build this protocol for help me in this process
protocol CBNibInstanceableCellProtocol {
static func getCellXib() -> UINib?
static func getReuseIdentifier() ->String
}
and in your class you have to implement those methods like here
//example implementation
extension CBUsersAttendanceEmptyCell : CBNibInstanceableCellProtocol
{
static func getCellXib() -> UINib?
{
if Bundle.main.path(forResource: "CBUsersAttendanceEmptyCell", ofType: "nib") != nil
{
return UINib(nibName: "CBUsersAttendanceEmptyCell", bundle: nil)
}
return nil
}
static func getReuseIdentifier() ->String
{
return "CBUsersAttendanceEmptyCell"
}
}
then in your viewDidLoad you must do something like this
//example code
self.collectionView.register(CBUsersAttendanceAvatarCell.getCellXib(), forCellWithReuseIdentifier: CBUsersAttendanceAvatarCell.getReuseIdentifier())
self.collectionView.register(CBUsersAttendanceCountCell.getCellXib(), forCellWithReuseIdentifier: CBUsersAttendanceCountCell.getReuseIdentifier())
self.collectionView.register(CBUsersAttendanceEmptyCell.getCellXib(), forCellWithReuseIdentifier: CBUsersAttendanceEmptyCell.getReuseIdentifier())
in your cellForRow
if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: CBUsersAttendanceCountCell.getReuseIdentifier(), for: indexPath) as? CBUsersAttendanceCountCell
{
return cell
}
You must have defined the class for you view in your xib, this is very important check this pictures
Hope this helps