Transferring Data from one View to another in Swift 3 - ios

Question

Following Situation:
I have 2 Controllers, a ViewController and a CollectionViewController. The normal ViewController is supposed to collect data from the user and when the start button is clicked, an algorithm solves the problem and returns the result. The Result is supposed to be transferred to the CollectionViewController, and based on the solution the CollectionView will be built.
Below is the code I used for the start button. As you can see, the Algorithm is called, the results are stored in several variables and now I was trying to transfer the matrixArray to my CollectionViewController (its a first test). The CollectionViewController should use the data stored in this array to present some form of tableau
#IBAction func startButton(_ sender: Any) {
...
let solution = PrimalSimplex(problem: problem, currentSolution: currentSolution)
matrixArray = solution.0
basicArray = solution.1
maxArray = solution.2
currentSolutionArray = solution.3
isOptimal = solution.4
isCyceling = solution.5
let CollectionVC = storyboard?.instantiateViewController(withIdentifier: "CollectionView") as! CollectionViewController
CollectionVC.testMatrix = matrixArray
}
So far so good, the data arrives is available in the CollectionViewController after the start button is pushed. But when I try to use the data to build the CollectionView, I get an error message.
This is the code that I used in the collectionViewController to build the CollectionView (It worked before, with static values... the problems occur when I try to use values that the algorithm returns):
class CollectionViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
#IBOutlet weak var myCollectionView: UICollectionView!
// Creates an empty array for the values
var testMatrix = Array<Matrix>()
//Setup CollectionView: Table to display LPs
let reuseIdentifier = "cell"
var items = testMatrix[0] <----ERROR
// MARK: - UICollectionViewDataSource protocol
// tell the collection view how many cells to make
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return items.count
}
// make a cell for each cell index path
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
// get a reference to our storyboard cell
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath as IndexPath) as! MyCollectionViewCell
// Use the outlet in our custom class to get a reference to the UILabel in the cell
cell.myLabel.text = items[indexPath.item]
cell.backgroundColor = UIColor(red:0.94, green:0.94, blue:0.94, alpha:1.0) // make cell more visible in our example project
// Change shape of cells
cell.layer.cornerRadius = 8
return cell
}
....
The error is displayed at var items = testMatrix[0]:
Cannot use instance member 'testMatrix' within property initializer; property initializers run before 'self' is available
I can understand that Xcode has a problem here, because it can't be sure that the testMatrix has values stored.... I think that the problem. I tried to use if let/ guard statement, but that didnt solve the problem.
Any advice on how to fix it or whats actually wrong here?
Maybe there is a better way to transfer the data from the first VC to the other one?

Answer 1

You can't initialize property from other dependent property at the class level.
You should try to initialized in viewDidLoad.
var items: Matrix?
override func viewDidLoad() {
super.viewDidLoad()
if testMatrix.count>0{
items = testMatrix[0]
}
}