I'm working on an Android app where I have ViewMod...

# android

[Colton Idle]

I'm working on an Android app where I have ViewModel arch component and I observe a liveData in my fragment. I want to have a countdown textView that counts from 50 to 0 and "ticks" every second.

I plan on doing this by having this coroutine

viewModelScope.launch {
            var initVal = 100
            repeat(100) {
                _myViewData.value =
                    _myViewData.value?.copy(initVal.toString())
                initVal--
                delay(1000)
            }
        }

Is there anything really bad with this approach? The only thing I can think of is how would the ViewModel being cleared would affect this.

[Adam Powell]

probably easier to use a for loop, the VM being cleared will stop the countdown

[Adam Powell]

also relevant is that you will be running even when the app is in the background, also time skew is possible if anything blocks the main thread handler for long enough

[Adam Powell]

consider using the liveData {} builder

[Colton Idle]

@Adam Powell

1. what would the conditions be inside the for loop? just the usual int i = 0; ...?
2. VM being cleared will stop the countdown? So it won't for repeat()?

[Adam Powell]

for (value in 100 downTo 0)

[Adam Powell]

VM being cleared cancels viewModelScope, so any delay call currently in progress will throw CancellationException

[Colton Idle]

@Adam Powell I basically just want a chronometer that counts down. lol

I don't need any insane amount of accuracy, but def noted that if anything blocks main, it could skew. thanks for that tip.

[Colton Idle]

@Adam Powell thanks for the advice. It works for my needs!

Last thing though, what was the reasoning for swapping repeat() with for(value...

[Adam Powell]

just makes the code shorter 🙂

[Colton Idle]

Gotcha. I thought it was integral to cancellation/vm clearing

[Adam Powell]

nah

[Gonçalo Palaio]

I know that’s not what you asked, but you could handle the countdown in a custom view and just trigger it with the start value. (if it’s just a direct countdown to zero)

[Colton Idle]

@Gonçalo Palaio custom views scare me 😃