Kotlin DAO return null when try to access-CodePudding

I am new to Android development. When I try to access the id from the Room. I get null. Is there something I did wrong?

Language

@Entity(tableName = "language_table6")
data class Language(
    val isChecked: Boolean = false,
    val language: String,
    val isFavourite: Int = 0,
    @PrimaryKey(autoGenerate = true) val id: Int = 0

)

LanguageDao

@Query("SELECT id FROM language_table6 WHERE language = :language")
     fun getEnglishId(language: String): LiveData<Long>

FavouriteViewModel

class FavouriteViewModel @Inject constructor(
    val languageDao: LanguageDao
) : ViewModel() {
val favouriteLanguage = languageDao.getFavouriteLanguageByName().asLiveData()
// Try to access get the id in language model
val englishObject: LiveData<Long> = languageDao.getEnglishId("English")

fun onFavouriteLanguage(languageId: Int) = CoroutineScope(Dispatchers.IO).launch {
    languageDao.resetFavouriteLanguage()
    languageDao.setFavouriteLanguage(languageId)
}

}

FavouriteFragment

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        val binding = FavouriteBottomSheetBinding.bind(view)
        val favouriteAdapter = FavouriteAdapter(this)
        
        // Try to try to get the value from viewModel  
        val getEnglishId: LiveData<Long> = viewModel.englishObject

        d("readEnglishId", getEnglishId.value.toString())

CodePudding user response：

When you call getEnglishId.value, the database read hasn't completed and the LiveData contains the initial value null. You need to observe the LiveData in your fragment.

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    val binding = FavouriteBottomSheetBinding.bind(view)
    val favouriteAdapter = FavouriteAdapter(this)
        
    viewModel.englishObject.observe(viewLifecycleOwner) { id ->
        // Here you can use the live data value (id)
    }
}