lateinit 属性 mUserViewModel 尚未初始化

Question

我正在尝试读取我的数据库，因此我创建了一个编辑文本，我将在其中输入用户名和一个允许我搜索用户的按钮，但我在 class ListFragment : Fragment(), 上面写着 lateinit 属性 mUserViewModel 还没有初始化，请帮帮我 :(.

//实体

@Entity(tableName = "user_table")
data class User(
    @PrimaryKey(autoGenerate = true)
    val id: Int,
    val firstName: String,
    val lastName: String,
    val age: Int
)

//道

@Dao
interface UserDao {

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    suspend fun addUser(user: User)
    @Query("SELECT * FROM user_table where firstName LIKE :search LIMIT 1")
    suspend fun readAllData(search : String) : User

}

//用户存储库

class UserRepository(private val userDao: UserDao) {
    suspend fun readAllData(user: String):User{
       return userDao.readAllData(user)
    }
}

//用户视图模型

class UserViewModel(application: Application): AndroidViewModel(application) {
    
   private lateinit var repository:UserRepository
    
    fun search( search : String):User{
        viewModelScope.launch {
            repository.readAllData(search)
        }
  
        return search(String())
    }

}

}

//class

class ListFragment : Fragment() {
    //erro(lateinit property mUserViewModel has not been initialized)
                lateinit var mUserViewModel:UserViewModel
                override fun onCreateView(
                    inflater: LayoutInflater, container: ViewGroup?,
                    savedInstanceState: Bundle?
                ): View? {
                    // Inflate the layout for this fragment
                    val view = inflater.inflate(R.layout.fragment_list, container, false)
            
                    val name = view.editTextTextNameee.text.toString()
                   val prueba = mUserViewModel.search(name)
            
                    if (prueba!=null){
            
                        textView1.text = prueba.firstName
                        textView2.text = prueba.lastName
                        textView3.text = prueba.age.toString()
                    }else {
                        Toast.makeText(context, " Unregistered use", Toast.LENGTH_SHORT).show()
                    }
            
            
                    view.floatingActionButton.setOnClickListener {
                        findNavController().navigate(R.id.action_listFragment_to_addFragment)
                    }
            
                    return view
                }
            }

Answer 1

这很正常，因为你的 Dao return 一个 LiveData 所以当你观察这个数据时 return 值是一个列表，而不仅仅是一个用户。我不知道你想做什么。但是你必须:

mUserViewModel.searchResult.observe(viewLifecycleOwner, Observer { 
             
              textViewName.text = it.name
              textViewLastName.text = it.lastname
              textViewAge.text = it.age
          })

您的查询将是：

@Query("SELECT * FROM user_table where name LIKE :search LIMIT 1") 
suspend fun searchUser(search : String) : User

然后在您的 mUserViewModel 中创建一个值 searchResult 和一个方法 search：

fun search(val search : String){
viewModelScope.launch {
    searchResult.postValue(dao.searchUser(search))
}

}

Answer 2

lateinit 未初始化的原因属性是您尚未创建 ViewModel 实例。你能试试这个吗

viewModel = ViewModelProvider(requireParentFragment(), factory).get(UserViewModel::class.java)

// 工厂将是视图模型的实例

您可以观察到实时数据更改 onviewCreated()

lateinit 属性 mUserViewModel 尚未初始化

lateinit property mUserViewModel has not been initialized

android-studio

android-room

android-livedata

android-viewmodel

kotlin-coroutines