android kotlin - Room LiveData ViewModel example

MainActivity.kt


package com.cfsuman.jetpack

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.text.method.ScrollingMovementMethod
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProviders
import kotlinx.android.synthetic.main.activity_main.*
import org.jetbrains.anko.doAsync
import java.util.*


class MainActivity : AppCompatActivity() {

    private lateinit var model: StudentViewModel

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

        // Make text view content scrollable
        textView.movementMethod = ScrollingMovementMethod()

        // Get the view model
        model = ViewModelProviders.of(this).get(StudentViewModel::class.java)

        // Observe the model
        model.allStudents.observe(this, Observer{ students->
            textView.text = ""
            for (student in students){
                textView.append("${student.id} | ${student.name}\n")
            }
        })


        // Insert data into table
        btn.setOnClickListener {
            doAsync {
                model.insert(Student(null, UUID.randomUUID().toString()))
               }
        }
    }
}

RoomSingleton.kt


package com.cfsuman.jetpack

import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import android.content.Context


@Database(entities = arrayOf(Student::class), version = 1, exportSchema = false)
abstract class RoomSingleton : RoomDatabase(){
    abstract fun studentDao():StudentDao

    companion object{
        private var INSTANCE: RoomSingleton? = null
        fun getInstance(context:Context): RoomSingleton{
            if (INSTANCE == null){
                INSTANCE = Room.databaseBuilder(
                    context,
                    RoomSingleton::class.java,
                    "roomdb")
                    .build()
            }

            return INSTANCE as RoomSingleton
        }
    }
}

RoomEntity.kt


package com.cfsuman.jetpack

import androidx.room.ColumnInfo
import androidx.room.Entity
import androidx.room.PrimaryKey

@Entity(tableName = "studentTbl")
data class Student(
    @PrimaryKey
    var id:Long?,

    @ColumnInfo(name = "uuid")
    var name: String
)

RoomDao.kt


package com.cfsuman.jetpack

import androidx.lifecycle.LiveData
import androidx.room.Dao
import androidx.room.Insert
import androidx.room.OnConflictStrategy
import androidx.room.Query

@Dao
interface StudentDao{
    @Query("SELECT * FROM studentTbl")
    fun allStudents(): LiveData<List<Student>>

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insert(student: Student)
}

StudentViewModel.kt


package com.cfsuman.jetpack

import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.LiveData
import android.app.Application


class StudentViewModel(application:Application): AndroidViewModel(application){
    private val db:RoomSingleton = RoomSingleton.getInstance(application)
    internal val allStudents : LiveData<List<Student>> = db.studentDao().allStudents()

    fun insert(student:Student){
        db.studentDao().insert(student)
    }
}

activity_main.xml


<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/rootLayout"
        tools:context=".MainActivity"
        android:background="#fdfdfc">
    <Button
            android:text="Insert Data"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/btn"
            android:layout_marginTop="8dp"
            app:layout_constraintTop_toTopOf="parent"
            android:layout_marginStart="8dp"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            android:layout_marginEnd="8dp"/>
    <TextView
            android:text=""
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/textView"
            app:layout_constraintEnd_toEndOf="parent"
            android:layout_marginEnd="16dp"
            app:layout_constraintStart_toStartOf="parent"
            android:layout_marginStart="16dp"
            android:layout_marginTop="16dp"
            app:layout_constraintTop_toBottomOf="@+id/btn"
            android:textAppearance="@style/Base.TextAppearance.AppCompat.Medium"
            android:textColor="#3F51B5"
            tools:text="TextView"
            android:padding="16dp"
    />
</androidx.constraintlayout.widget.ConstraintLayout>

gradle settings


apply plugin: 'kotlin-kapt'

dependencies {
    // ViewModel and LiveData
    def lifecycle_version = "2.0.0"
    implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version"

    // Room support
    def room_version = "2.1.0-alpha04"
    implementation "androidx.room:room-runtime:$room_version"
    kapt 'androidx.room:room-compiler:2.1.0-alpha04'

    // Anko Commons
    implementation "org.jetbrains.anko:anko-commons:0.10.5"
}

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