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【Android】DataBinding のバインディング式で sealed class を使う方法

2021/03/17に公開
Android
Kotlin
tech

instanceofを使う

==を使いたくなってしまうところですが、instanceofを使います。

android:visibility="@{viewModel.resource instanceof Resource.Success ? View.VISIBLE : View.GONE}"

実装例

以下の実装は、サーバーから記事を取得するサンプルです。

取得の状況に応じてレイアウトを切り替えます。

app/build.gradle

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

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }

    // 追加: DataBinding で使用
    buildFeatures {
        dataBinding = true
    }
}

dependencies {
    // 追加: ViewModelScopeで使用
    implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.3.0'
    // 追加: ViewModelの初期化で使用
    implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'
    // 追加: 記事取得処理を遅延させるために使用
    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.4.2'
    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.4.2'
}

MainActivity.kt

class MainActivity : AppCompatActivity() {

    private val viewModel: MainViewModel by lazy {
        ViewModelProvider(this).get(MainViewModel::class.java)
    }

    private val binding: ActivityMainBinding by lazy {
        DataBindingUtil.setContentView(this, R.layout.activity_main)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding.apply {
            lifecycleOwner = this@MainActivity
            viewModel = this@MainActivity.viewModel
        }
        viewModel.fetchArticle(articleId = 1)
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<layout>
    <data>
        <variable
            name="viewModel"
            type="com.yass.databindingsealedsample.MainViewModel" />
        <import type="android.view.View" />
        <import type="com.yass.databindingsealedsample.Resource" />
    </data>

    <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">

        <ProgressBar
            android:id="@+id/progress"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:visibility="@{viewModel.resource instanceof Resource.Loading ? View.VISIBLE : View.GONE}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <androidx.constraintlayout.widget.ConstraintLayout
            android:id="@+id/article_layout"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent">

            <TextView
                android:id="@+id/article_title"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="@{viewModel.resource.data.title}"
                android:textSize="20sp"
                android:textStyle="bold"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

            <TextView
                android:id="@+id/article_description"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                android:text="@{viewModel.resource.data.description}"
                android:visibility="@{viewModel.resource instanceof Resource.Success ? View.VISIBLE : View.GONE}"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/article_title" />

        </androidx.constraintlayout.widget.ConstraintLayout>

        <androidx.constraintlayout.widget.ConstraintLayout
            android:id="@+id/error_layout"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:visibility="@{viewModel.resource instanceof Resource.Error ? View.VISIBLE : View.GONE}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent">

            <ImageView
                android:id="@+id/error_image"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@color/purple_500"
                android:src="@drawable/ic_launcher_foreground"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

            <TextView
                android:id="@+id/error_message"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                android:text="データの取得に失敗しました"
                android:textSize="16sp"
                app:layout_constraintTop_toBottomOf="@+id/error_image" />

        </androidx.constraintlayout.widget.ConstraintLayout>
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

MainViewModel.kt

class MainViewModel : ViewModel() {

    private val repository: ArticleRepository by lazy {
        ArticleRepository()
    }

    private val _resource = MutableLiveData<Resource<Article>>()
    val resource: LiveData<Resource<Article>> = _resource

    fun fetchArticle(articleId: Int) {
        _resource.postValue(Resource.Loading())
        viewModelScope.launch(Dispatchers.IO) {
            val article = repository.fetchArticle(articleId)
            _resource.postValue(article)
        }
    }
}

ArticleRepository.kt

class ArticleRepository {

    private val remote: RemoteDataSource by lazy {
        RemoteDataSource()
    }

    suspend fun fetchArticle(articleId: Int): Resource<Article> = remote.fetchArticle(articleId)
}

RemoteDataSource.kt

class RemoteDataSource {

    suspend fun fetchArticle(articleId: Int): Resource<Article> {
        var article: Article? = null
        // サーバーからデータを取得すると仮定して、5秒遅延
        GlobalScope.launch(Dispatchers.IO) {
            delay(5000)
            article = Article(id = articleId, title = "記事のタイトル", description = "記事の説明")
        }.join()
        return article?.let {
            Resource.Success(it)
        } ?: Resource.Error(message = "Failed to get the article")
    }
}

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