[Kotlin][Android] AAC ViewModel + LiveData+ Databinding 이용 숫자 증감

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

    var num = MutableLiveData<Int>()

    init {
        num.value = 0
    }

    fun addNum(){
        num.value = num.value?.plus(1)
    }

    fun subtractNum(){
        num.value = num.value?.minus(1)

    }
}

1. Gradle 세팅

 

plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-android-extensions'
    id 'kotlin-kapt'
}

android {
    ...

    buildFeatures{
        dataBinding true
    }
    ...

}

dependencies {
    ...
    
	// LifeCycle
    def lifecycle_version = "2.2.0"
    
    // ViewModel
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
    
    // LiveData
    implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
    implementation "androidx.activity:activity-ktx:1.1.0"

}

2. ViewModel 먼저 만들어줍니다.

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

	// 표출할 숫자
    var num = MutableLiveData<Int>()

	// 초기화
    init {
        num.value = 0
    }

	// +1 씩 더하기
    fun addNum(){
        num.value = num.value?.plus(1)
    }

	// -1 씩 빼기
    fun subtractNum(){
        num.value = num.value?.minus(1)

    }
}

 

3. 레이아웃 및 바인딩

<?xml version="1.0" encoding="utf-8"?>
<layout
    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">
    
    <!---A--------------------------------------------------->
    <data>
        <variable
            name="viewModel"
            type="com.example.kotlinexample.ViewModel" />
    </data>
    <!-------------------------------------------------------->
    
    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <TextView
            android:id="@+id/tv_num"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{Integer.toString(viewModel.num)}"
            android:textColor="@color/black"
            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="0.37" />

        <Button
            android:id="@+id/btn_add"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="296dp"
            android:text="+"
            android:onClick="@{()->viewModel.addNum()}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent" />

        <Button
            android:id="@+id/btn_subtract"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="248dp"
            android:text="-"
            android:onClick="@{()->viewModel.subtractNum()}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent" />

    </androidx.constraintlayout.widget.ConstraintLayout>

</layout>

A 부분의 데이터 태그를 명시해줍니다.

 

4. View 와 ViewModel 연동 및 lifecycleOwner 생명주기 관리

class MainActivity : AppCompatActivity() {

    private lateinit var mBinding: ActivityMainBinding
    private val mModel : ViewModel by viewModels()


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

        mBinding = DataBindingUtil.setContentView(this,R.layout.activity_main)

        mBinding.lifecycleOwner = this
        mBinding.viewModel = mModel

    }
}