DataBinding

gradle 추가

buildFeatures {
        dataBinding = true
}

xml에 최상단을 layout으로 바꿔줘야 한다.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<layout 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"
    tools:context=".MainActivity">
    <data>
        <variable
            name="user"
            type="com.example.review.User" />
        <variable
            name="viewmodel"
            type="com.example.review.MyViewModel" />
    </data>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@{viewmodel.score.toString()}"
            android:textSize="30sp"/>
        <androidx.fragment.app.FragmentContainerView
            android:id="@+id/fragmentContainerView"
            android:layout_width="match_parent"
            android:layout_height="370dp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            android:name="com.example.review.Fragment1"
            tools:layout="@layout/fragment1" />

        <androidx.fragment.app.FragmentContainerView
            android:layout_width="match_parent"
            android:layout_height="370dp"
            android:name="com.example.review.Fragment2"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/fragmentContainerView"
            app:layout_constraintVertical_bias="0.0"
            tools:layout="@layout/fragment2"
            android:id="@+id/TODO" />

    </LinearLayout>


</layout>

ViewModel을 Databinding에 사용하기

MyViewModel

class MyViewModel: ViewModel() {
    val score = MutableLiveData<Int>(1)
    fun scorePlus() {
        score.value = (score.value ?:0) + 1
    }
    fun scoreMinus() {
        score.value = (score.value ?:0) - 1
    }
}

MainActivity

class MainActivity : AppCompatActivity() {
    private var binding: ActivityMainBinding? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding?.root)

        var user2 =  User("su","mi")
        binding!!.user = user2

        val mainViewModel: MyViewModel by viewModels()
        binding!!.lifecycleOwner = this
        binding!!.viewmodel =  mainViewModel


    }
}

여기서 주의할점은 LiveData를 DataBinding에서 사용할 때 LiveData의 Lifecycleowner가 현재 activity(Main)라는 것을 명시해줘야 합니다.

Android Developer
참고자료