Start and Stop Timer Project

Dependancy reuired in app build.gradle

implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.5.0-rc01'

Activity Code

class MainActivity : AppCompatActivity() {

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    
    setContentView(R.layout.activity_main)
    val viewModel = ViewModelProvider(this).get(CountDownViewModel::class.java)
    bt_start_timer.setOnClickListener { viewModel.starTimer() }
    bt_stop_timer.setOnClickListener { viewModel.stopTimer() }

    viewModel.countValue.observe(this, Observer {
        tv_timer_time.text = it.toString()
    })


}

}

CountDownViewModel which have start and stop timer code

class CountDownViewModel : ViewModel() {

private var _countValue = MutableLiveData<Int>(0)

val countValue: LiveData<Int>
    get() = _countValue
    
private lateinit var job: Job


fun starTimer() {
    job = viewModelScope.launch {
        while (true) {
            delay(1000)
            _countValue.value = _countValue.value?.plus(1)
        }
    }

    job.start()
}

fun stopTimer() {
    if(job.isInitialized)
     job.cancel()
}

}

APP Snapshots: