Confused about LiveData Observe - android-livedata

Question

My situation is When user enter loading fragment, check LoggedIn, true go straight to MainFragment, false jump to LoginFramgnet.
here is LoadingFragment:
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
Logger.t(LoadingFragment::class.java.simpleName).i("onCreateView")
val binding = LoadingFragmentBinding.inflate(inflater, container, false)
subscribeUi()
return binding.root
}
fun subscribeUi(){
val factory: LoadingViewModelFactory = InjectorUtils.provideLoadingViewModelFactory()
val viewModel: LoadingViewModel = ViewModelProviders.of(this, factory).get(LoadingViewModel::class.java)
Logger.t(LoadingFragment::class.java.simpleName).i("viewModel = " + viewModel.toString())
viewModel.checkLogin()
viewModel.isToLogin.observe(viewLifecycleOwner, Observer {
if (it){
findNavController().navigate(R.id.action_loading_fragment_to_garden_fragment)
}else{
Logger.t(LoadingFragment::class.java.simpleName).i("to start login")
findNavController().navigate(R.id.start_login)
}
})
}
here is LoadingViewModel:
class LoadingViewModel(
private val loadingRepository: LoadingRepository
) : ViewModel() {
val isToLogin: MediatorLiveData<Boolean> = MediatorLiveData()
fun checkLogin(){
isToLogin.addSource(loadingRepository.checkLogin()) {
isToLogin.value = it
}
}
}
here is the Loadingrepository:
fun checkLogin() : MutableLiveData<Boolean> {
val data: MutableLiveData<Boolean> = MutableLiveData()
api.httpGet(SDBUrl.CHECK_LOGIN).enqueue(object : Callback<Map<String, Any>>{
override fun onFailure(call: Call<Map<String, Any>>, t: Throwable) {
data.value = false
}
override fun onResponse(call: Call<Map<String, Any>>, response: Response<Map<String, Any>>) {
val result = response.body()
if (result != null && result.containsKey("success")){
val isLogin = result["success"] as Boolean
data.value = isLogin
}else{
data.value = false
}
}
})
return data
}
when logged in, popbackto LoadingFragment,isToLogin observe execute else immediately, LoginFragment start agagin. when I debug, wait a while on LoginFragment popBackStack, then goback to Loading Fragment,isToLogin observe execute true.so I am very confused, how can I fix this.

Answer 1

Finally, I solved this problem as follow.
class LoadingViewModel(
private val loadingRepository: LoadingRepository
) : ViewModel() {
fun checkLogin(): MediatorLiveData<Boolean> {
val isToLogin : MediatorLiveData<Boolean> = MediatorLiveData()
isToLogin.addSource(loadingRepository.checkLogin()) {
Logger.t(LoadingViewModel::class.java.simpleName).i("it = $it")
isToLogin.value = it
}
return isToLogin
}
}
then in LoadingFragment,:
loadingViewModel.checkLogin().observe(viewLifecycleOwner, Observer {
Logger.i("isToLogin = $it")
if (it) {
findNavController().navigate(R.id.action_loading_fragment_to_garden_fragment)
} else {
findNavController().navigate(R.id.start_login)
}
})