Swift retain UISegmentedControl values in UITableViewCells - ios

Question

I'm creating a quiz app with custom cells that include a label of questions and then an answer coming from a UISegmentedControl.
The values of the segmentedcontrols get changed when scrolling and this leads to an inaccurate score. I understand that this is due to UITableView reusing cells.
My tableview's datasource in my main vc is simply the labels for all my questions coming from a plist file.
The code for my custom tableviewcell class is
class QuestionsTableViewCell: UITableViewCell {
#IBOutlet weak var questionLabel: UILabel!
#IBOutlet weak var selection: UISegmentedControl!
var question: String = "" {
didSet {
if (question != oldValue) {
questionLabel.text = question
}
}
}
override func awakeFromNib() {
super.awakeFromNib()
// Initialization code
}
override func setSelected(_ selected: Bool, animated: Bool) {
super.setSelected(selected, animated: animated)
// Configure the view for the selected state
}
//Just for testing
#IBAction func segmentChanged(_ sender: UISegmentedControl) {
print("value is ", sender.selectedSegmentIndex);
}
}
where the View is stored in an .XIB file.
And the code for my main vc is
class ViewController: UIViewController, UITableViewDataSource {
let questionsTableIdentifier = "QuestionsTableIdentifier"
#IBOutlet var tableView:UITableView!
var questionsArray = [String]();
var questionsCellArray = [QuestionsTableViewCell]();
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
let path = Bundle.main.path(forResource:
"Questions", ofType: "plist")
questionsArray = NSArray(contentsOfFile: path!) as! [String]
tableView.register(QuestionsTableViewCell.self,
forCellReuseIdentifier: questionsTableIdentifier)
let xib = UINib(nibName: "QuestionsTableViewCell", bundle: nil)
tableView.register(xib,
forCellReuseIdentifier: questionsTableIdentifier)
tableView.rowHeight = 108;
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return questionsArray.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(
withIdentifier: questionsTableIdentifier, for: indexPath)
as! QuestionsTableViewCell
let rowData = questionsArray[indexPath.row]
cell.question = rowData
return cell
}
#IBAction func calculate(_ sender: UIButton) {
var score = 0
for cell in tableView.visibleCells as! [QuestionsTableViewCell] {
score += cell.selection.selectedSegmentIndex
}
let msg = "Score is, \(score)"
print(msg)
}
#IBAction func reset(_ sender: UIButton) {
for cell in tableView.visibleCells as! [QuestionsTableViewCell] {
cell.selection.selectedSegmentIndex = 0;
}
}
}
What I'd like to do is just keep track of all 'selection' changes of the Questions cells in an array, and then use that array in cellForRowAt. I'm just confused as to how i can dynamically keep track of changes from a view in another class. I'm new to Swift and would like to solve this is a proper MVC fashion. Thanks

Answer 1

Instead of a simple string array as data source create a class holding the text and the selected index
class Question {
let text : String
var answerIndex : Int
init(text : String, answerIndex : Int = 0) {
self.text = text
self.answerIndex = answerIndex
}
}
Declare questionArray as
var questions = [Question]()
Populate the array in viewDidLoad with
let url = Bundle.main.url(forResource: "Questions", withExtension: "plist")!
let data = try! Data(contentsOf: url)
let questionsArray = try! PropertyListSerialization.propertyList(from: data, format: nil) as! [String]
questions = questionsArray.map {Question(text: $0)}
In the custom cell add a callback and call it in the segmentChanged method passing the selected index, the property question is not needed, the label is updated in cellForRow of the controller
class QuestionsTableViewCell: UITableViewCell {
#IBOutlet weak var questionLabel: UILabel!
#IBOutlet weak var selection: UISegmentedControl!
var callback : ((Int) -> ())?
#IBAction func segmentChanged(_ sender: UISegmentedControl) {
print("value is ", sender.selectedSegmentIndex)
callback?(sender.selectedSegmentIndex)
}
}
In cellForRow add the callback and update the model in the closure
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: questionsTableIdentifier, for: indexPath) as! QuestionsTableViewCell
let question = questions[indexPath.row]
cell.questionLabel.text = question.text
cell.selection.selectedSegmentIndex = question.answerIndex
cell.callback = { index in
question.answerIndex = index
}
return cell
}
To reset the segmented controls in the cells set the property in the model to 0 and reload the table view
#IBAction func reset(_ sender: UIButton) {
questions.forEach { $0.answerIndex = 0 }
self.tableView.reloadData()
}
Now you could calculate the score directly from the model instead of the view.

Answer 2

Don't try to use cells to hold information. As the user scrolls through your table view, cells that scroll out of view will get recycled and their field settings will be lost. Also, newly dequeued cells will have the settings from the last time they were used.
You need to refactor your code to read/write information into a data model. Using an array of Structs as a data model is a reasonable way to go. (Or, as vadian suggests in his answer, and array of Class objects, so you get reference semantics.)
You have an IBAction segmentChanged() in your custom cell class. The next trick is to notify the view controller when the user changes the selection, and to update cells when you set them up in cellForRowAt.
I suggest defining a protocol QuestionsTableViewCellProtocol, and have the view controller conform to that protocol:
protocol QuestionsTableViewCellProtocol {
func userSelected(segmentIndex: Int, inCell cell: UITableViewCell)
}
}
Add a delegate property to your QuestionsTableViewCell class:
class QuestionsTableViewCell: UITableViewCell {
weak var delegate: QuestionsTableViewCellProtocol?
//The rest of your class goes here...
}
Update your cell's segmentChanged() method to invoke the delegate's userSelected(segmentIndex:inCell:) method.
In your view controller's cellForRowAt, set the cell's delegate to self.
func userSelected(segmentIndex: Int, inCellCell cell: UITableViewCell) {
let indexPath = tableView.indexPath(for: cell)
let row = indexPath.row
//The code below assumes that you have an array of structs, `dataModel`, that
//has a property selectedIndex that remembers which cell is selected.
//Adjust the code below to match your actual array that keeps track of your data.
dataModel[row].selectedIndex = segmentIndex
}
Then update cellforRowAt() to use the data model to set the segment index on the newly dequeued cell to the correct index.
Also update your calculate() function to look at the values in your dataModel to calculate the score, NOT the tableView.
That's a rough idea. I left some details out as "an exercise for the reader." See if you can figure out how to make that work.