How to send and receive UISlider value from one view controller to another

Question

I'm trying to use NotificationCenter to send slider values (audio volume) to another view controller which contains the all the audio engine that I need. From the sender VC I tried this:

@IBAction func vol1ChangedFromMixer(sender: UISlider) {
    NotificationCenter.default.post(name: Notification.Name(rawValue: "vol1FromMixer"), object: nil)
    }

And then at receiver VC, in viewDidLoad:

//vol from mixer
    NotificationCenter.default.addObserver(self, selector: #selector(vol1FromMixer(_:)), name: Notification.Name(rawValue: "vol1FromMixer"), object: nil)

And later at the same receiver VC:

//vol from mixer function
      @objc func vol1FromMixer() {
        _engine.setAmpGain(Double(sender.value)*2.0, ofTrack: sender.tag)
}

Got error use of unresolved identifier "sender" at the receiver VC. For sure I'm not ready with the UISlider kind of values that can be sent. Any suggestion?

as error stated, your `sender` variable in `vol1FromMixer ` is not defined. what you expected to get by `sender`? what type? — Tien Nguyen, May 18 '18 at 20:48

Tien Nguyen · Accepted Answer · 2018-05-20T19:16:07.493

0

You need to pass sender from vol1ChangedFromMixer method. You can use this method, and pass sender in userInfo. Then retrieve it in vol1FromMixer

Sometheing like

@IBAction func vol1ChangedFromMixer(sender: UISlider) {
    NotificationCenter.default.post(name: Notification.Name(rawValue: "vol1FromMixer"), object: nil, userInfo: ["slider": sender])
}

@objc func vol1FromMixer(_ notification: Notification) {
    guard let sender = notification.userInfo["slider"] as? UISlider
         else { return }
    _engine.setAmpGain(Double(sender.value)*2.0, ofTrack: sender.tag)
}

edited May 20 '18 at 19:16

answered May 18 '18 at 20:51

Tien Nguyen

599
4
13

Great, it worked! Just had to change to (_ notification: Notification) inside function. – Sktsalad May 19 '18 at 16:37

score 0 · Answer 2 · answered Jul 08 '20 at 11:28

A solution without Notification

1. create class 'DataManager'

this class is in my `Tools.swift` file

class DataManager {
    ///to call function in VCA from VCB
    ///needs three elements:
    /// 1. this class
    /// 2. 'DataManager.shared.fistVCYouNameIt1 = self’ in VCA in viewDidLoad()
    /// 3. 'DataManager.shared.fistVCYouNameIt1.myFuncInVcAToCallFromVcB()' in VCB (execute function in VCA)
    static let shared = DataManager()
    var fistVCYouNameIt1 = ViewController1() //class Name
    var fistVCYouNameIt2 = ViewController1() //class Name
    //var fistVCYouNameIt3 ...
}//end class DataManager

2. in you VCA in viewDidLoad():

override func viewDidLoad() {
    super.viewDidLoad()
    DataManager.shared.fistVCYouNameIt1 = self //to call func ‘myFuncInVcAToCallFromVcB ()’ from VCB in VCA. Without this e.g. your outlets are not accessible within VCA, when called from VCB

    //other code
}

3. in your VCB

The point in your code VCB to call function in VCA:

...
DataManager.shared.fistVCYouNameIt.myFuncInVcAToCallFromVcB() //execute func in VCA 
...

4. in your VCA:

func myFuncInVcAToCallFromVcB (){
    //your code here
}