Swift 4 - Xcode 9 store Array in UserDefaults via Json

Question

Goal: is to save array data to be retrieved by next session

Approach: encode the array to Json, store in UserDefaults, then retrieve data and decode to the array. Maybe a better way, assume wrapping in Json is the best way to transport to UserDefaults

I think my encode and save to UserDefault works & I can return the object and print a size... don't know how to decode back to my array?

    var matrixArray =  [matrixItem]()
    var returnArray: Decodable = [returnMatrixItem]()

    let encoder = JSONEncoder()
    let decoder = JSONDecoder()

     @IBAction func restoreFrom(_ sender: Any) {
        let   restoredJson: Data = UserDefaults.standard.data(forKey: "storeArray")!

// its here that i can't determine how to decode the return value to my array
// error: cannot invoke decode with an argument list of type([Decodeable], from Data:)
        try! JSONDecoder().decode([returnArray.self], from: restoredJson)
        print("return json size \(restoredJson)")*

    }

    @IBAction func appendItem(_ sender: Any) {
     if let newValue = newItem.text  {
  print(newValue)
            newItem.text = "  "
     let    itemToAdd = matrixItem(matrixName: newValue, matrixDescription: itemDescription.text!)

         matrixArray.append(itemToAdd)
        print(matrixArray)
        let  jsonData = try! encoder.encode(matrixArray)
        print("Print json data \(jsonData)")
        UserDefaults.standard.set(jsonData, forKey: "storeArray")

        }

    }