Android Studio Room data without livedata

Question

I got the following Room database and want to output the name of a random user in a textview. Unfortunately running the code yields the output: kotlin.unit inside the textview. My files look like that:

MainActivity.kt

class MainActivity : AppCompatActivity() {

    private lateinit var mNameViewModel: NameViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        mNameViewModel = ViewModelProvider(this).get(NameViewModel::class.java)

        val btn = findViewById<Button>(R.id.btn_addName)
        val tv = findViewById<TextView>(R.id.tv_showName)

        btn.setOnClickListener {
            val text = findViewById<EditText>(R.id.et_enterName)?.text.toString()
            val name = Name(0, text)

            // Add Data to Database
            mNameViewModel.addName(name)
            Toast.makeText(applicationContext, "Successfully added $text.", Toast.LENGTH_LONG).show()

            val randomName = mNameViewModel.getRandomName()

            // Without .toString() I get an error, with it it displays kotlin.unit
            tv.text = randomName.toString() 
        }

    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/tv_showName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.133" />

    <EditText
        android:id="@+id/et_enterName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPersonName"
        android:hint="Name"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.244" />

    <Button
        android:id="@+id/btn_addName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.379" />

</androidx.constraintlayout.widget.ConstraintLayout>

Name.kt

@Entity(tableName = "name_data")
data class Name (
    @PrimaryKey(autoGenerate = true) val id: Int,
    @ColumnInfo(name = "name") val name: String
)

NameDao.kt

@Dao
interface NameDao {

    @Insert
    fun addName(name: Name)

    @Query("SELECT name FROM name_data ORDER BY RANDOM() LIMIT 1")
    fun getRandomName(): String
}

NameDatabase.kt

@Database(entities = [Name::class], version = 1, exportSchema = false)
abstract class NameDatabase: RoomDatabase() {

    abstract fun nameDao(): NameDao

    companion object{
        @Volatile
        private var INSTANCE: NameDatabase? = null

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

NameRepository.kt

class NameRepository(private val nameDao: NameDao) {

     fun getRandomName() { nameDao.getRandomName() }

     fun addName(name: Name) { nameDao.addName(name) }
}

NameViewModel.kt

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

    private val repository: NameRepository

    init {
        val nameDao = NameDatabase.getDatabase(application).nameDao()
        repository = NameRepository(nameDao)
    }

    fun addName(name: Name) {
        viewModelScope.launch(Dispatchers.IO){
            repository.addName(name)
        }
    }

    fun getRandomName() {
        viewModelScope.launch(Dispatchers.IO){
            repository.getRandomName()
        }
    }
}

This is how the output of textview when pressing the button.

The database gets populated though.

Apreciate any help to get the data displayed. Thank you!

Answer 1

The issue is that in your getRandomNumber method inside viewmodel you don't return anything that's why you get kotlin.unit . You should instead make sure to return a value

A possible solution would be the following.

1. Create a method inside your dao which takes a number and returns that row (this will be essentially the random name)
2. From your repo call that method with a random number you could use Random.getNextInt not sure how do you get a random
3. From your view model call that method
4. From your button onClick call the viewModel method

Make sure to use suspend where applicable in order to get a result. For the case that I showcased above that would be to launch a coroutine in view level and make the rest of the calls (vm,repo,dao) suspend

Answer 2

So after some testing and back and forth this is what I have and it seems to be working. If anyone has some things to bring in I gladly accept them and a big thanks to georkost for all the usefull tips!

// No changes made to database

@Entity(tableName = "name_data")
data class Name (
    @PrimaryKey(autoGenerate = true) val id: Int,
    @ColumnInfo(name = "name") val name: String
)

//*********************************************************************************

// Changed return type from Query to LiveData<String> (was just String before)

@Dao
interface NameDao {

    @Insert
    fun addName(name: Name)

    @Query("SELECT name FROM name_data ORDER BY RANDOM() LIMIT 1")
    fun getRandomName(): LiveData<String>    // HERE
}

//*********************************************************************************

// Changed getRandomMeal from fun to val

class NameRepository(private val nameDao: NameDao) {

     val getRandomMeal: LiveData<String> = nameDao.getRandomName()  // HERE

     fun addName(name: Name) { nameDao.addName(name) }
}

//*********************************************************************************

// Added getRandomName val, initialized it and removed the fun

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

    val getRandomName: LiveData<String>             // HERE
    private val repository: NameRepository

    init {
        val nameDao = NameDatabase.getDatabase(application).nameDao()
        repository = NameRepository(nameDao)
        getRandomName = repository.getRandomMeal    // HERE
    }

    fun addName(name: Name) {
        viewModelScope.launch(Dispatchers.IO){
            repository.addName(name)
        }
    }
}

//*********************************************************************************

// Changed the last row to observe the LiveData and display it in the Text View

class MainActivity : AppCompatActivity() {

    private lateinit var mNameViewModel: NameViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        mNameViewModel = ViewModelProvider(this).get(NameViewModel::class.java)

        val btn = findViewById<Button>(R.id.btn_addName)
        val tv = findViewById<TextView>(R.id.tv_showName)

        btn.setOnClickListener {
            val text = findViewById<EditText>(R.id.et_enterName)?.text.toString()
            val name = Name(0, text)

            // Add Data to Database
            mNameViewModel.addName(name)
            Toast.makeText(applicationContext, "Successfully added $text.", Toast.LENGTH_LONG).show()

            // HERE
            mNameViewModel.getRandomName.observe(this, Observer { String -> tv.text = String })


        }
    }
}