Updating the tableview of superclass - ios

Question

I followed a tutorial to make a MVVP model tableview
My tableViewController is called MyProfileController and looks like this:
class MyProfileController: UITableViewController {
fileprivate var viewModel: ProfileViewModel?
override func viewDidLoad() {
super.viewDidLoad()
tableView.register(UserInfoCell.self, forCellReuseIdentifier: UserInfoCell.identifier)
viewModel = ProfileViewModel()
tableView.dataSource = self.viewModel
}
}
}
Rather than defining UITableViewDataSource in MyProfileController, I create a view model called ProfileViewModel and pass it to tableView.dataSource. The ProfileViewModel is defined like the following:
class ProfileViewModel: NSObject {
fileprivate var profile: UserProfile?
var items = [ProfileViewModelItem]()
init() {
super.init()
//...
}
}
extension ProfileViewModel: UITableViewDataSource {
// ...
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath) as! UserInfoCell
cell.userDetailTextView.delegate = self
return cell
}
// ...
}
extension ProfileViewModel: UITextViewDelegate {
func textViewDidChange(_ textView: UITextView) {
print(textView.text)
////////////////
// ERROR HERE //
// tableView.beginUpdates()
// tableView.endUpdates()
////////////////
}
}
I'm setting a delegate to UITextView inside the cellForRowAt indexPath method so that textViewDidChange delegate method will be called when user types in the textview. Up to this point works. The problem is that I cannot update the tableView from here. How can I update the tablView of MyProfileController?

Answer 1

You can use closures to send messages to your table view controller.
Declare a closure variable in your data source object.
class ProfileViewModel: NSObject {
var textViewDidChange: (() -> Void)?
// If you need to send some data to your controller, declare it with type. In your case it's string.
// var textViewDidChange: ((String) -> Void)?
}
Send your message from your text field delegate to your newly created variable like this.
func textViewDidChange(_ textView: UITextView) {
self.textViewDidChange?()
// If you need to send your string, do it like this
// self.textViewDidChange?(textView.text)
}
As you can guess, your variable textViewDidChange is still nil so no message will pass through. So we should declare that now.
In your view controller where you have access to your data source, set the value of your closure.
class MyProfileController: UITableViewController {
fileprivate var viewModel: ProfileViewModel?
override func viewDidLoad() {
super.viewDidLoad()
tableView.register(UserInfoCell.self, forCellReuseIdentifier: UserInfoCell.identifier)
viewModel = ProfileViewModel()
tableView.dataSource = self.viewModel
// Set the closure value here
viewmodel.textViewDidChange = { [unowned self](/* if you are sending data, capture it here, if not leave empty */) in
// Do whatever you like with your table view here.
// [unowned self] could sound tricky. It's whole another subject which isn't in the scope of this question. But of course there are some great answers here about it. Simply put, if you don't use it, you'll create a memory leak.
}
}
}

Answer 2

There are lots of ways to do this. And it depends on your team's coding pattern rules or whatever should we call that.
But this is what I usually do: The view model has a protocol for reloadingData. Or better yet, the protocol of all my view models has a base class for such reloadData, like so:
protocol ProfileDelegate: BaseViewModelDelegate {
}
class ProfileViewModel: NSObject {
//....
}
And here goes the BaseViewModelDelegate:
/// The Base Delegate of all ViewModels.
protocol BaseViewModelDelegate: NSObjectProtocol {
/// Ask the controller to reload the data.
func reloadTableView()
/// Presents an alert/
func presentAlert(title: String, message: String, okayButtonTitle: String, cancelButtonTitle: String?, withBlock completion: LLFAlertCallBack?)
}
As you can see, there's a reloadTableView method. And that's where I reload the tableView of my controllers if needed. But again, there are lots of ways to do this. I hope this helps!

Answer 3

You can have your DataSource out of your view controller, but it’s important to follow the correct separation, I suggest this kind of approach because it can help you with tests.
Use a protocol to define the behavior of your view model (for testing you can have a mock view model that implement this protocol):
protocol ProfileViewModelType {
var items: [ProfileViewModelItem]
var textViewDidChange: ((UITextView) -> Void)?)
//...
}
Then implement your viewModel with the data:
class ProfileVieModel: ProfileViewModelType {
var items = [ProfileViewModelItem]()
//...
}
Then inject in your DataSource object the view model and use it to populate your table view and to manage all the callbacks:
class ProfileTableViewDataSource: NSObject, UITableViewDataSource {
private var viewModel: ProfileViewModelType!
init(viewModel: ProfileViewModelType) {
self.viewModel = viewModel
}
func textViewDidChange(_ textView: UITextView) {
print(textView.text)
viewModel.textViewDidChange?(textView)
}
}
Finally in your view controller you can observe the view model callbacks and manage there your actions:
class YourViewController: UIViewController {
private var dataSource: ProfileTableViewDataSource?
private var viewModel: ProfileViewModelType = ProfileViewModel()
override func viewDidLoad() {
super.viewDidLoad()
dataSource = ProfileTableViewDataSource(viewModel: viewModel)
tableView.dataSource = dataSource
bindViewModel()
}
func bindViewModel() {
viewModel.textViewDidChange = { [weak self] textView in
// ...
}
}
}