I have a tableview, to configure a cell (from VC),
cell.model = dataSource[indexpath.row]
In the didSet of cell.model, I am initialising the cell contents.
Cell has 3 buttons, tapping on which, I am informing the VC through CellDelegate
protocol CellDelegate {
func didTapButton1(model: Model)
func didTapButton2(model: Model)
func didTapButton3(model: Model)
}
My concern:-
I don't want to pass the model here (as it is already associated with the Cell - somehow need to fetch the model from cell)
I would like to call didTapButton() without the parameter. Then in the VC,
extension VC: CellDelegate {
//I need to fetch the model associated with the cell.
func didTapButton1() { }
func didTapButton2() { }
func didTapButton3() { }
}
I could achieve this using closure, but it is not preferred here.
Any help would be appreciated.*
I'm guessing the reason why you don't want to pass the model is because having a model in all three methods look like code duplication. Well, if you have look at the delegates in the framework, such as UITableViewDelegate, UITextFieldDelegate, most, if not all, of them accept the thing that they are a delegate of as the first parameter. All the methods in UITableViewDelegate has a tableView parameter. Therefore, it would be OK for you to follow the pattern as well:
protocol CellDelegate {
func didTapButton1(_ cell: Cell)
func didTapButton2(_ cell: Cell)
func didTapButton3(_ cell: Cell)
}
Personally, I would write only one method in this delegate:
protocol CellDelegate {
func didTapButton(_ cell: Cell, buttonNumber: Int)
}
In the VC extension, you simply check buttonNumber to see which button is pressed:
switch buttonNumber {
case 1: button1Tapped()
case 2: button2Tapped()
case 3: button3Tapped()
default: fatalError()
}
// ...
func button1Tapped() { ... }
func button2Tapped() { ... }
func button3Tapped() { ... }
Related
I have a UIView which displays some information such as a user's Name and more, including a list of objects that all get pulled from my database. This works fine.
However, I now have a ViewController that gets presented on top of the current ViewController. In this presented ViewController, I am adding Data to my Database. When dismissing that view, I want the original ViewController to update all of its content to be up to date.
Right now, all my views are getting layedout in ViewDidLoad, meaning that they only really get loaded once and don't reload later on. I have managed to update Layout by calling self.view.layoutIfNeeded(), but if I understand correctly, this only updates constraint. Of course, I could call a new init of my original view controller. This would make it reload, but I would like to avoid that.
Another Idea I had was to set up all my content in the ViewWillAppear, which should maybe then update anytime my view controller is about to be visible. However, I don't know how to go about doing this. Can I just move all my setup code to viewWillAppear? Does this have any disadvantages?
TLDR: Is there a way to update a stackview with new elements without having to reload the full ViewController over ViewWillAppear?
The UITableView element works very smoothly with database data. If you fetch the data from your database inside viewDidLoad in your first view controller, and store it in an array, the UITableView (if you set up its dataSource correctly) will automatically populate the table with the new values from the second view controller. With this method, there is no need to use ViewWillAppear at all.
It sounds like as of now, you're using Views (inside a VStack)? to display individual objects from the database. If you want to keep whatever custom style/layout you're using with your views, this can be done by defining a custom subclass of UITableViewCell and selecting the "Also create XIB file" option. The XIB file lets you customize how the cells in your UITableView look.
Here is a simple example to show the database values in the first view controller automatically updating. I didn't include the custom XIB file (these are all default UITableViewCells), to keep it streamlined.
FIRST VIEW CONTROLLER
import UIKit
import CoreData
class ViewController: UIViewController {
#IBOutlet weak var dataTable: UITableView!
var tableRows: [DataItem] = []
func loadData() {
let request: NSFetchRequest<DataItem> = DataItem.fetchRequest()
do {
tableRows = try Global_Context.fetch(request)
} catch {
print("Error loading data: \(error)")
}
}
override func viewDidLoad() {
super.viewDidLoad()
dataTable.dataSource = self
loadData()
}
#IBAction func goForward(_ sender: UIButton) {
self.performSegue(withIdentifier: "toSecond", sender: self)
}
}
extension ViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return tableRows.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "dataTableCell", for: indexPath)
cell.textLabel?.text = tableRows[indexPath.row].name
return cell
}
}
let Global_Context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
func saveContext () {
if Global_Context.hasChanges {
do {
try Global_Context.save()
} catch {
let nserror = error as NSError
print("Error saving database context: \(nserror), \(nserror.userInfo)")
}
}
}
SECOND VIEW CONTROLLER:
import UIKit
import CoreData
class AddViewController: UIViewController {
#IBOutlet weak var itemEntry: UITextField!
override func viewDidLoad() {
super.viewDidLoad()
itemEntry.delegate = self
}
#IBAction func addNewItem(_ sender: UIButton) {
let newDataItem = DataItem(context: Global_Context)
newDataItem.name = itemEntry.text
saveContext()
}
#IBAction func goBack(_ sender: UIButton) {
self.performSegue(withIdentifier: "toFirst", sender: self)
}
}
extension AddViewController: UITextFieldDelegate {
func textFieldShouldReturn(_ textField: UITextField) -> Bool {
textField.endEditing(true)
return true
}
}
Main.storyboard:
Once you set up your view controller as a UITableViewDataSource (as in the example code), the table view should make things simpler by eliminating any need to manually manage individual Views.
Is this the functionality you were looking for? (Note about the example: it was set up in Xcode with "Use Core Data" enabled.)
Here is a link to the official documentation:
https://developer.apple.com/documentation/uikit/uitableview
I need to dismiss ViewController from the corresponding TableViewCell, but I'm getting an error message, "Value of type 'TableViewCell' has no member 'dismiss'"
self.dismiss(animated: true, completion: nil)
How can I dismiss the ViewController from the corresponding TableViewCell
If you just want the solution and don't really care about the structure of the application, the following will work. As the other guy mentioned, this probably isn't the best way to structure your application.
Make a delegate to the TableViewCell.
protocol TableViewDismissDelegate {
func dismissViewController()
}
class YourTableViewClass {
var delegate: TableViewDismissDelegate?
...
}
In your table view delegate:
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = mainTableView.dequeueReusableCell(withIdentifier: YourTableViewClass.identifier, for: indexPath) as! YourTableViewClass
cell.delegate = self
return cell
}
Make sure your view controller conforms to your protocol:
extension YourViewController: TableViewDismissDelegate {
func dismissViewController() {
self.dismiss(animated: true, completion: nil)
}
}
You cannot say self.dismiss in a UITableViewCell, as dismiss is a UIViewController command, and a UITableViewCell is not a UIViewController.
What I like to do in this situation is get a reference to the UIViewController so that I can tell it to dismiss. To do so, I create a UIResponder extension, like this:
extension UIResponder {
func next<T:UIResponder>(ofType: T.Type) -> T? {
let r = self.next
if let r = r as? T ?? r?.next(ofType: T.self) {
return r
} else {
return nil
}
}
}
That extension just walks up the responder chain looking for an instance of any class we care to name. So now self.next(ofType: UIViewController.self) is the view controller, and we can tell it to dismiss.
(There are plenty of other solutions, but that's just a solution that I happen to like.)
It may be argued, however, that you should never have gotten yourself in this situation in the first place. It is no business of a UITableViewCell to be telling anyone to dismiss anything. This is a violation of model-view-controller principles. You should probably be looking at a completely different architecture here.
Here is the code with the delegate process suggested...
in main view controller...
protocol FilterDelegate: class {
func onRedFilter()
func onGreenFilter()
func onBlueFilter()
func onUnfiltered()
}
class ViewController: UIViewController, FilterDelegate, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
----
// Increase red color level on image by one.
func onRedFilter() {
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "filterSegue" {
let dest = segue.destinationViewController as! CollectionViewController
dest.filterDelegate = self
}
}
in collection view controller...
var filterDelegate: FilterDelegate?
func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
print("Cell \(indexPath.row) selected")
guard let filterDelegate = filterDelegate else {
print("Filter delegate wasn't set!")
return
}
switch indexPath.row {
case 0:
filterDelegate.onRedFilter()
case 1:
filterDelegate.onGreenFilter()
case 2:
filterDelegate.onBlueFilter()
case 3:
filterDelegate.onUnfiltered()
default:
print("No available filter.")
}
Right now...the code stops at the guard block and prints the error message. The switch block is not executed on any press of a cell.
Your theory in your second last sentence is correct - when you call storyboard.instantiateViewControllerWithIdentifier in the "child" view controller, you are actually creating an entirely new instance of your main view controller. You are not getting a reference to the existing main view controller, which is why the methods you're calling are not having any effect.
There are several ways to achieve what you're trying to do, including the delegate pattern or using closures. Here's a sketch of what it could look like using a delegate protocol:
protocol FilterDelegate: class {
func onRedFilter()
func onGreenFilter()
func onBlueFilter()
func onUnfiltered()
}
class MainViewController: UIViewController, FilterDelegate {
// implement these as required
func onRedFilter() { }
func onGreenFilter() { }
func onBlueFilter() { }
func onUnfiltered() { }
// when we segue to the child view controller, we need to give it a reference
// to the *existing* main view controller
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let dest = segue.destination as? ChildViewController {
dest.filterDelegate = self
}
}
}
class ChildViewController: UIViewController {
var filterDelegate: FilterDelegate?
func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
// ...
guard let filterDelegate = filterDelegate else {
print("Filter delegate wasn't set!")
return
}
switch indexPath.row {
case 0:
filterDelegate.onRedFilter()
case 1:
filterDelegate.onGreenFilter()
case 2:
filterDelegate.onBlueFilter()
case 3:
filterDelegate.onUnfiltered()
default:
print("No available filter.")
}
}
}
Another option would be to provide closures on ChildViewController for every function on MainViewController that the child needs to call, and set them in prepareForSegue. Using a delegate seems a bit cleaner though since there are a bunch of functions in this case.
I started working on this question app.
I began by tableView of the categories:
For data exchange, I decided to use a protocol:
protocol Category {
func data(object:AnyObject)
}
In the first ViewController has the following code:
class ViewController: UIViewController {
var items:[String] = ["Desktop","Tablet","Phone"]
let CategoriesData:Category? = nil
override func viewDidLoad() {
super.viewDidLoad()
CategoriesData?.data(items)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
In the second ViewController (tableView in Container) have the following code:
class CategoriesViewController: UIViewController, UITableViewDataSource, UITableViewDelegate, Category {
#IBOutlet var table: UITableView!
var items:[String] = []
func data(object: AnyObject) {
self.items = (object as? [String])!
print(object)
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.items.count
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell:TableViewCell = self.table.dequeueReusableCellWithIdentifier("SegueStage") as! TableViewCell
cell.nameLabel.text = items[indexPath.row]
return cell
}
}
For me, apparently it's all right. But nothing appeared on the simulator.
My question is: If the Container use to present another viewController as passing data by protocols should be done?
EDITED
I answered why the TO:s solution didn't work as intended, but I just realised that I haven't given a viable answer to how to use protocols as delegates for the ViewController -> ViewController communication. I'll leave the half-answer below until someone can possibly answer the full question better.
In the way protocol is used in your code, you define your protocol Category to be a delegate for instances of the type ViewController. When an instance of type ViewController is initialised in---and hence owned locally in the scope of---some other class, the instance can delegate callbacks to the owning class.
The problem is that your CategoriesViewController does not contain any instances of type ViewController. We note that both these classes are, in themselves, subclasses of UIViewController, but none of them contain instances of one another. Hence, your CategoriesViewController does indeed conform to protocol Category, by implemented the protocol method data(...), but there's no ViewController instance in CategoriesViewController that can do callbacks to this function. Hence, your code compile file, but as it is, method data(...) in CategoriesViewController will never be called.
I might be mistaken, but as far as I know, protocol delegates are used to do callbacks between models (for model in MVC design) and controllers (see example below), whereas in your case, you want a delegate directly between two controllers.
As an example of model-delegate-controller design, consider some custom user control, with some key property value (e.g. position in rating control), implemented as a subclass of UIView:
// CustomUserControl.swift
protocol CustomUserControlDelegate {
func didChangeValue(value: Int)
}
class CustomUserControl: UIView {
// Properties
// ...
private var value = 0 {
didSet {
// Possibly do something ...
// Call delegate.
delegate?.didChangeValue(value)
}
}
var delegate: CustomUserControlDelegate?
// ... some methods/actions associated with your user control.
}
Now lets assume an instance of your CustomUserControl is used in a a view controller, say ViewController. Your delegate functions for the custom control can be used in the view controller to observe key changes in the model for CustomUserControl, much like you'd use the inherent delegate functions of the UITextFieldDelegate for UITextField instances (e.g. textFieldDidEndEditing(...)).
For this simple example, use a delegate callback from the didSet of the class property value to tell a view controller that one of it's outlets have had associated model update:
// ViewController.swift
Import UIKit
// ...
class ViewController: UIViewController, CustomUserControlDelegate {
// Properties
// ...
#IBOutlet weak var customUserControl: CustomUserControl!
// Instance of CustomUserControl in this UIViewController
override func viewDidLoad() {
super.viewDidLoad()
// ...
// Custom user control, handle through delegate callbacks.
customUserControl.delegate = self
}
// ...
// CustomUserControlDelegate
func didChangeValue(value: Int) {
// do some stuff with 'value' ...
}
}
I have a function within a UICollectionViewCell that requires access to the
hosting UIViewController. Currently 'makeContribution()' can't be accessed:
What is the proper way of accessing the host UIViewController that has the desired function?
Thanks to the insightful responses, here's the solution via delegation:
...
...
...
{makeContribution}
This is a mildly controversial question - the answer depends a little on your philosophy about MVC. Three (of possibly many) options would be:
Move the #IBAction to the view controller. Problem solved, but it might not be possible in your case.
Create a delegate. This would allow the coupling to be loose - you could create a ContributionDelegate protocol with the makeContribution() method, make your view controller conform to it, and then assign the view controller as a weak var contributionDelegate: ContributionDelegate? in your cell class. Then you just call:
contributionDelegate?.makeContribution()
Run up the NSResponder chain. This answer has a Swift extension on UIView that finds the first parent view controller, so you could use that:
extension UIView {
func parentViewController() -> UIViewController? {
var parentResponder: UIResponder? = self
while true {
if parentResponder == nil {
return nil
}
parentResponder = parentResponder!.nextResponder()
if parentResponder is UIViewController {
return (parentResponder as UIViewController)
}
}
}
}
// in your code:
if let parentVC = parentViewController() as? MyViewController {
parentVC.makeContribution()
}
Well, CollectionView or TableView?
Anyway, Set your ViewController as a delegate of the cell. like this:
#objc protocol ContributeCellDelegate {
func contributeCellWantsMakeContribution(cell:ContributeCell)
}
class ContributeCell: UICollectionViewCell {
// ...
weak var delegate:ContributeCellDelegate?
#IBAction func contributeAction(sender:UISegmentedControl) {
let isContribute = (sender.selectedSegmentIndex == 1)
if isContribute {
self.delegate?.contributeCellWantsMakeContribution(self)
}
else {
}
}
}
class ViewController: UIViewController, UICollectionViewDataSource, ContributeCellDelegate {
// ...
func collectionView(_ collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
cell = ...
if cell = cell as? ContributeTableViewCell {
cell.delegate = self
}
return cell
}
// MARK: ContributeCellDelegate methods
func contributeCellWantsMakeContribution(cell:ContributeCell) {
// do your work.
}
}