How to read ble peripheral value correctly in swift? - ios

Question

I am trying to read a byte array from my one view controller to another, please find my code below.
From my First View
class First: UIViewController {
var myByteArray = [UInt8](repeating:0, count: 20)
viewDidLoad(){
......}
Few statements later hers where I read my data in a function
func passThis(){
let ReceiveData = rxCharacteristic?.value
if let ReceiveData = ReceiveData {
let ReceivedNoOfBytes = ReceiveData.count
myByteArray = [UInt8](repeating: 0, count: ReceivedNoOfBytes)
(ReceiveData as NSData).getBytes(&myByteArray, length: ReceivedNoOfBytes)
print("Data Received ",myByteArray)
}
This is my Second View that I'm trying to read my array from First View
class Second: UIViewController {
var myByteArray2 = [UInt8](repeating: 0, count: 20)
viewDidLoad(){
super.viewDidLoad()
let fvc = First()
myByteArray2 = fvc.myByteArray
print(myByteArray2)
}
Now I have [11,12,13,14,15,16,17,18,19,20] from myByteArray
but have [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0] from myByteArray2 ?
Can somebody help?
Also how do I clear the readValue buffer in rxCharacterstic before writing and reading new values?
Any help/comments appreciated.
Thanks
EDIT -> How my passing is done
From BLECentral
class BLECentral: ...
var centralManager: CBCentralManager!
//After Scanning and connecting
func centralManager(_central: CBCentralManager, didConnect peripheral: CBPeripheral){
peripheral.delegate = self
peripheral.discoverServices([BLEUUID])
//Once connected, move to new view controller to manager incoming and outgoing data
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let firstVC = storyboard.instantiateViewController(withIdentifier: "First") as! First
firstVC.peripheral = peripheral
navigationController?.pushViewController(firstVC, animated: true)
}
Now in my First under prepare for segue block I'm passing the peripheral like this
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.destination is Second
{
let vc2 = segue.destination as? Second
vc2.periperal = blePeripheral
}
}

Answer 1

You are creating a new First view controller from your Second view controller, instead of accessing the one already created.
//Create a new View Controller
let fvc = First()
So you have two First that are made now. What you want to do is access the already created First view controller. Assuming there is no other way, you want to have a "Singleton". This is a very bad way to handle this, as I'll explain later, and there is most likely a better way, but I'm going to give a solution to access First from Second if they never communicate, but First is already created.
If you declare in First a piece of code like:
static let shared = First()
Then that singleton can be accessed via
let first = First.shared
That being said, that's a really bad way of handling communication between view controllers. If you call Second from First, you should pass the data from First to Second (or you could pass a reference of First to Second so Second can access First).
There is generally good ways to pass data between view controllers in the
func prepare(for segue: UIStoryboardSegue, sender: Any?)
method before you navigate. Whenever, whatever, makes the Second view controller should pass it the data it needs.
Lastly, another reason the Singleton view controller is a terrible idea is that it gets away from the MVC concept. So if you can't pass the proper data to Second, you probably need a new class that handles the data for you that both First and Second can work with which is the Model in MVC.