sealed class DataHolder<out T> {
    data class Success<out T>(val value: T) : DataHolder<T>()
    data class Error(val cause: Throwable) : DataHolder<Nothing>()
}

disposables += Usecase5sec().getSingle()
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe (
        {s -> liveData.value = DataHolder.Success(s)},
        {e -> liveData.value = DataHolder.Error(e)}
    )


val viewModel = ViewModelProviders.of(this).get(VmDashboard::class.java)
viewModel.liveData.observe(this, object: Observer<DataHolder<String>> {
    override fun onChanged(dataHolder:DataHolder<String>?) {
        when(dataHolder){
            is DataHolder.Success -> vh?.setData(dataHolder.value)
            is DataHolder.Error -> vh?.setError(dataHolder.cause)
        }
    }
})