LoginViewModel.kt

val email = MutableLiveData<String>()
    val password = MutableLiveData<String>()
    val isEmailAndPasswordValid = MediatorLiveData<Boolean>().apply {
        addSource(email) { validate() }
        addSource(password) { validate() }
    }

    private fun validate() {
        isEmailAndPasswordValid.value =
            email.value.orEmpty().isNotEmpty() && password.value.orEmpty().isNotEmpty()
    }