如何读取 DataBaseRoom 并显示 textView

Question

我正在使用 dataBaseRoom 进行练习，我为他们创建了一个按钮，可以让我读取数据库，我想输入用户的名称，当按下按钮（读取数据库）时会反映我，他的名字，最后texview中的姓名和年龄，问题是我不知道如何在textView中显示数据。

我想要执行操作的活动

//实体

@Entity(tableName = "user_table")
data class User(
    @PrimaryKey(autoGenerate = true)@ColumnInfo(name = "id") 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 ORDER BY id ASC")
    fun readAllData(): LiveData<User>
    
}

//数据库

@Database(entities = [User::class], version = 1, exportSchema = false)
abstract class UserDatabase : RoomDatabase() {
    abstract fun userDao(): UserDao
    companion object {
        @Volatile
        private var INSTANCE: UserDatabase? = null

        fun getDatabase(context: Context): UserDatabase{
            val tempInstance = INSTANCE
            if(tempInstance != null){
                return tempInstance
            }
            synchronized(this){
                val instance = Room.databaseBuilder(
                    context.applicationContext,
                    UserDatabase::class.java,
                    "user_database"
                ).build()
                INSTANCE = instance
                return instance
            }
        }
    }
}

//存储库

 class UserRepository(private val userDao: UserDao) {
    
    val readAllData: LiveData<User> = userDao.readAllData()

    suspend fun addUser(user: User){
        userDao.addUser(user)
    }

}

//视图模型

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

    val readAllData: LiveData<User>
    private val repository: UserRepository

    init {
        val userDao = UserDatabase.getDatabase(application).userDao()
        repository = UserRepository(userDao)
        readAllData = repository.readAllData
    }

    fun addUser(user: User) {
        viewModelScope.launch(Dispatchers.IO) {
            repository.addUser(user)
        }
    }

}

我想在这个类中添加我的 texview

  mUserViewModel = ViewModelProvider(this).get(UserViewModel::class.java)
        mUserViewModel.readAllData.observe(viewLifecycleOwner, Observer {

            textView1.text = it.firstName
            textView2.text = it.lastName
            textView3.text = it.age.toString()


        })

Answer 1

在您的片段中，将观察者添加到 LiveData 并在观察者中设置 TextView 值。

See the documentation here.

---

要获取字段中最新添加的用户的数据，您可以使用这个（检查.size或.length是否适合您）：

    mUserViewModel.readAllData.observe(viewLifecycleOwner, Observer { users ->
        if (users != null) {
            for (user in users) { // I'm not sure about kotlin syntax 
                if (user.firstName == enteredFirstName &&
                             user.lastName == enteredLastname) {   
                    textViewFirstName.text = user.firstName
                    textViewLastName.text = user.lastName
                    textViewAge.text = user.age.toString()