How to trigger a function via variable change (binding) - swiftui

Question

I have a timer view which I want to reuse and I want to start the timer by my binding variable running like this:
Unfortunately I am (too?) tired this morning to find a solution how to do that. :(
Maybe my solution is bad and there is a much easier way!?
struct TimerView: View {
#State var hours : Int = 0
#State var minutes : Int = 0
#State var seconds : Int = 0
#State var hundred : Int = 0
#Binding var running : Bool
let timer = Timer.publish (every: 0.01, on: .main, in: .common)
#State var cancellable : Cancellable?
func start() {
self.cancellable = timer.connect()
}
func stop() {
cancellable!.cancel()
}

Answer 1

You can do the following, create this extension
extension Binding {
func didSet(execute: #escaping (Value) ->Void) -> Binding {
return Binding(
get: {
return self.wrappedValue
},
set: {
let snapshot = self.wrappedValue
self.wrappedValue = $0
execute(snapshot)
}
)
}
}
And the the parent view, not TimerView you can have something like this
//[...]
TimerView(running: $running.didSet{ value in /* your code or function here*/ })
//[...]
Check my answer here
UPDATE 1
Based on the comment what I understood is that the you want to start/stop the timer from outside the TimerView.
I found a couple ways to do that
First one declare the TimerView as a variable in the parent view
struct ContentView: View {
#State var running: Bool = false
#State var timerView: TimerView? = nil
init() {
timerView = TimerView(running: $running)
}
// rest...
}
But depending on your init it can be a pain so I created a small extension that allows you to reference the view like so
extension View {
func `referenced`<T>(by reference: Binding<T>) -> (Self?){
DispatchQueue.main.async { reference.wrappedValue = self as! T }
return self
}
}
The usage of this extension is rather simple
struct ContentView: View {
#State var running: Bool = false
#State var timerView: TimerView? = nil
var body: some View {
TimerView(running: $running).referenced(by: $timerView)
}
}
Then you can control it using for instance a button Button(action: self.timerView.start()) { Text("Start Timer") }
If tested this code against your TimerView but seems there's something wrong in the stop() code. I commented the line cancellable!.cancel() and added a print instead and everything is working as expected.
Here's the test code that I used in Xcode Playground
I hope this is the answer you're looking for.