LiveData observer triggering previous response

Question

In my login page when I click on login button with valid email and password, then it goes into homepage. and then when i logged out from there and redirect to login page . then i face is when i clicks on login then it first enter into homepage [even I input any credential or not]. i wants that whenever login button clicks it checks one time. i think its observing previous data.

in login fragment when i click login button i called this method:

   private fun loginCheck(email: String, pass: String) {

   val loginViewModel = ViewModelProvider(this)[LoginViewModel::class.java]
    loginViewModel.loginResponse(requireContext(), email, pass, object : ProgressCallback {
        val opusLoader = OpusProgressLoader(requireContext())
        override fun onStart() {

            opusLoader.customDialogFunctionality(isCancelable = true)
        }

        override fun onFinish() {

            opusLoader.customDialogFunctionality(isCancelable = false)
        }
    })
        .observe(viewLifecycleOwner, Observer { loginPojo ->

            val accessToken = loginPojo.access_token
            if (accessToken.isNotEmpty()) {
                 Navigation.findNavController(requireView()).navigate(R.id.homepage)
                 requireActivity().finish()

            } else Toast.makeText(requireContext(), "Failed", Toast.LENGTH_SHORT).show()
        })
}

my Viewmodel for this :

    class LoginViewModel(application: Application) : AndroidViewModel(application) {

private val loginRepo = AuthRepoImpl.getInstance()


    fun loginResponse(
        context: Context,
        username: String,
        password: String,
        progressCallback: ProgressCallback
    ): LiveData<LoginPojo> {

        return  loginRepo.cLoginResponse(context, username, password,progressCallback)
    }
}

and repository method:

    override fun cLoginResponse(
    context: Context,
    username: String,
    password: String,
    progressCallback: ProgressCallback
): MutableLiveData<LoginPojo> {

    progressCallback.onStart()
    val apiServices = rInstance.getRetrofitInstance()?.create(ApiServices::class.java)
    val requestBody = LoginBody(username, password)

    val call = apiServices?.getUser( requestBody)

    try {
        call?.enqueue(object : Callback<LoginPojo> {
            override fun onResponse(
                call: Call<LoginPojo>,
                response: Response<LoginPojo>
            ) {
                
                progressCallback.onFinish()
                mLivedata.postValue(loginResponse!!)
            }

            override fun onFailure(call: Call<LoginPojo>, t: Throwable) {
                progressCallback.onFinish()
                Toast.makeText(context, "Login Failed", Toast.LENGTH_SHORT).show()
            }
        })
    } catch (e: Exception) {
        e.printStackTrace()
        progressCallback.onFinish()
        Toast.makeText(context, "Login Failed", Toast.LENGTH_SHORT).show()
    }
    return mLivedata
}

Answer 1

Clear your live data on your logout Action.

yourlivedata.postValue(null)

Answer 2

Your problem is within the repository, I see you use mLivedata variable which looks like an object member field, you return it every time you call cLoginResponse, which saves the result inside and will give you the latest value when you first observe it again. That's why you always get the wrong value from the second call forward.

You have 2 options to fix this:

• Create a new LiveData object in the repository cLoginResponse method. This will give a new result for each call.
• Don't return LiveData object in method, instead return a kotlin Flow or suspend mechanism for API case. It takes time to get used to but it is worthy. Expose a Flow object from the Repository layer, then simply call asLiveData() when you want to observe it from ViewModel to View:

fun cLoginResponse(...) = callbackFlow<LoginPojo> { }

suspend function is another good option too, and it's already supported by Retrofit:

suspend fun cLoginResponse(...): LoginPojo { }

Answer 3

You can try to clear the ViewModel when you log in and redirect to the login fragment.