[ Kotlin+MVVM ] Migrate ViewModel class from Java to Kotlin

Author: li2

app/src/main/java/me/li2/android/architecture/ui/articles/view/ArticlesFragment.kt

@@ -49,7 +49,7 @@ class ArticlesFragment : DaggerFragment() {
 
  mViewModel.uiModel.observe(this, Observer { uiModel -> updateView(uiModel) })
 
- mViewModel.loadingIndicatorVisibility.observe(this, Observer { visible -> setLoadingIndicatorVisibility(visible!!) }) // TODO why Found String?
+ mViewModel.loadingIndicator.observe(this, Observer { visible -> setLoadingIndicatorVisibility(visible!!) }) // TODO why Found String?
 
  mViewModel.snackbarMessage.observe(this, Observer { message -> showSnackBar(message!!) }) // TODO why Found String?
  }

app/src/main/java/me/li2/android/architecture/ui/articles/viewmodel/ArticlesViewModel.java

@@ -0,0 +1,133 @@
+package me.li2.android.architecture.ui.articles.viewmodel
+
+import android.arch.lifecycle.LiveData
+import android.arch.lifecycle.MutableLiveData
+import android.arch.lifecycle.Transformations
+import android.arch.lifecycle.ViewModel
+import android.util.Log
+import android.view.View
+import arch.NoNetworkException
+import arch.Resource
+import arch.Status
+import io.reactivex.Completable
+import io.reactivex.functions.Action
+import io.reactivex.functions.Consumer
+import me.li2.android.architecture.R
+import me.li2.android.architecture.data.model.Article
+import me.li2.android.architecture.data.repository.ArticlesRepository
+import me.li2.android.architecture.ui.articles.view.ArticlesNavigator
+import me.li2.android.architecture.utils.BaseResourceProvider
+import java.util.*
+
+/**
+ * ViewModel to expose states for the list of articles view, and handle all user actions.
+ *
+ * - Ask data from repository [ArticlesViewModel.mRepository], and then
+ * construct the source data to view data which contains all UI state.
+ *
+ * - Expose streams for view to subscribe the UI state,
+ * such as [ArticlesViewModel.getUiModel], [ArticlesViewModel.getLoadingIndicatorVisibility]
+ *
+ * - Expose public methods for view to handle user actions,
+ * such as force pull-refresh [ArticlesViewModel.forceUpdateArticles]
+ *
+ * - For user action in the sub-view, such as click or check in the list view item,
+ * implement [Action] or [Consumer] in the ViewModel
+ * [ArticlesViewModel.handleArticleTaped], and then
+ * pass it as parameter to ViewHolder constructor [ArticleItem.ArticleItem].
+ *
+ * @author Weiyi Li on 13/7/18 | https://github.com/li2
+ */
+
+private const val TAG = "ArticlesViewModel"
+
+class ArticlesViewModel(private val mRepository: ArticlesRepository,
+ private val mResourceProvider: BaseResourceProvider,
+ private val mNavigator: ArticlesNavigator
+) : ViewModel() {
+
+ /**
+ * Live stream emits true if the progress indicator should be displayed, false otherwise.
+ */
+ val loadingIndicator = MutableLiveData<Boolean>()
+
+ /**
+ * Live stream emits the string which should be displayed in the snackbar.
+ */
+ val snackbarMessage = MutableLiveData<String>()
+
+ /**
+ * Live stream emits the [ArticlesUiModel] which is the model for the articles list screen.
+ */
+ val uiModel: LiveData<ArticlesUiModel> =
+ Transformations.map(getArticleItems()) { resource ->
+ loadingIndicator.value = resource.status == Status.LOADING
+
+ if (resource.status == Status.ERROR) {
+ if (resource.throwable is NoNetworkException) {
+ snackbarMessage.value = mResourceProvider.getString(R.string.status_no_connect)
+ } else {
+ Log.d(TAG, "Failed to get UI model : ${resource.errorMessage}")
+ snackbarMessage.value = resource.errorMessage
+ }
+ }
+
+ if (resource.data != null) {
+ constructArticlesUiModel(resource.data)
+ } else {
+ null
+ }
+ }
+
+ /**
+ * Convert [Article] (raw data model) to [ArticleItem] (view data model)
+ * @return
+ */
+ private fun getArticleItems(): LiveData<Resource<List<ArticleItem>>> =
+ Transformations.map(mRepository.loadArticles()) { resource ->
+ var articleItems: MutableList<ArticleItem>? = null
+ if (resource.data != null) {
+ articleItems = ArrayList()
+ for (article in resource.data) {
+ articleItems.add(constructArticleItem(article))
+ }
+ }
+ Resource<List<ArticleItem>>(resource.status, articleItems, resource.errorMessage, resource.code, resource.throwable)
+ }
+
+ private fun constructArticlesUiModel(articleItems: List<ArticleItem>): ArticlesUiModel {
+ val isArticlesListVisible = !articleItems.isEmpty()
+ val isNoArticlesViewVisible = !isArticlesListVisible
+
+ return ArticlesUiModel(
+ isArticlesListVisible,
+ articleItems,
+ isNoArticlesViewVisible,
+ mResourceProvider.getString(R.string.no_articles_all)
+ )
+ }
+
+ /** Convert raw data from server to view data which contains all the UI state.
+ because UI doesn't care too much details about the raw data. notebyweiyi */
+ private fun constructArticleItem(article: Article): ArticleItem {
+ return ArticleItem(
+ article.title,
+ article.description,
+ article.imageHref,
+ Consumer { view -> handleArticleTaped(article, view) }
+ )
+ }
+
+ private fun handleArticleTaped(article: Article, sharedElement: View) {
+ mNavigator.openArticleDetails(article.id, sharedElement)
+ }
+
+ /**
+ * Trigger a force update of the articles.
+ */
+ fun forceUpdateArticles(): Completable? {
+ loadingIndicator.value = true
+ // TODO
+ return null
+ }
+}

app/src/main/java/me/li2/android/architecture/ui/articles/viewmodel/ArticlesViewModel.kt

@@ -0,0 +1,31 @@
+package me.li2.android.architecture.ui.articles.viewmodel
+
+import android.arch.lifecycle.ViewModel
+import android.arch.lifecycle.ViewModelProvider
+import me.li2.android.architecture.data.repository.ArticlesRepository
+import me.li2.android.architecture.ui.articles.view.ArticlesNavigator
+import me.li2.android.architecture.utils.BaseResourceProvider
+import javax.inject.Inject
+
+/**
+ * Created by weiyi on 24/7/18.
+ * https://github.com/li2
+ *
+ * TODO why cannot inject directly in the ViewModel
+ */
+class ArticlesViewModelFactory @Inject
+constructor() : ViewModelProvider.NewInstanceFactory() {
+
+ @Inject
+ lateinit var mRepository: ArticlesRepository
+
+ @Inject
+ lateinit var mNavigator: ArticlesNavigator
+
+ @Inject
+ lateinit var mResourceProvider: BaseResourceProvider
+
+ override fun <T : ViewModel> create(modelClass: Class<T>): T {
+ return ArticlesViewModel(mRepository, mResourceProvider, mNavigator) as T
+ }
+}