Re-factored bunch of code with focus on conciseness, nullability and code re-usability

Author: AkshayChordiya

app/src/main/java/com/akshay/newsapp/adapter/NewsArticlesAdapter.kt

@@ -14,7 +14,9 @@ import kotlinx.android.synthetic.main.news_article_item.view.*
  * @author Akshay Chordiya
  * @since 5/23/2017.
  */
-class NewsArticlesAdapter(val listener: (NewsArticles) -> Unit) : RecyclerView.Adapter<NewsArticlesAdapter.NewsHolder>() {
+class NewsArticlesAdapter(
+        private val listener: (NewsArticles) -> Unit
+) : RecyclerView.Adapter<NewsArticlesAdapter.NewsHolder>() {
 
     /**
      * List of news articles
@@ -56,5 +58,6 @@ class NewsArticlesAdapter(val listener: (NewsArticles) -> Unit) : RecyclerView.A
      */
     fun replaceItems(items: List<NewsArticles>) {
         newsArticles = items
+        notifyDataSetChanged()
     }
 }

app/src/main/java/com/akshay/newsapp/api/ApiResponse.java

@@ -3,31 +3,33 @@ package com.akshay.newsapp.api
 import android.arch.lifecycle.LiveData
 import com.akshay.newsapp.BuildConfig
 import com.akshay.newsapp.model.NewsSource
+import com.akshay.newsapp.model.network.Resource
 import com.akshay.newsapp.utils.LiveDataCallAdapterFactory
 import retrofit2.Retrofit
 import retrofit2.converter.gson.GsonConverterFactory
 import retrofit2.http.GET
 
 /**
- * Fetch all the latest news article from Google news
+ * Fetch all the latest news article from Google news.
  *
  * @author Akshay Chordiya
  * @since 5/23/2017.
  */
 interface NewsSourceService {
 
     /**
-     * Retrieves all the latest news article from Google news
+     * Retrieves all the latest news article from Google news.
      */
     @GET("articles?source=google-news&apiKey=" + BuildConfig.NEWS_API_KEY)
-    fun getNewsSource(): LiveData<ApiResponse<NewsSource>>
+    fun getNewsSource(): LiveData<Resource<NewsSource>>
 
     /**
      * Kinda like a static block in Java
      */
     companion object Factory {
-        val BASE_URL = "https://newsapi.org/v1/"
+        private const val BASE_URL = "https://newsapi.org/v1/"
 
+        // TODO: Move to DI.
         fun getNewsSourceService(): NewsSourceService {
             return Retrofit.Builder()
                     .baseUrl(BASE_URL)

app/src/main/java/com/akshay/newsapp/api/NewsSourceService.kt

@@ -9,6 +9,7 @@ import com.akshay.newsapp.model.NewsArticles
 /**
  * Abstracts access to the news database
  */
+//TODO: Use inheritance for code re-usability.
 @Dao
 interface NewsArticlesDao {
 

app/src/main/java/com/akshay/newsapp/db/NewsArticlesDao.kt

@@ -0,0 +1,26 @@
+package com.akshay.newsapp.model.network
+
+/**
+ * A generic class that holds a value with its loading status.
+ * @param <T>
+</T> */
+data class Resource<ResultType>(var status: Status, var data: ResultType? = null, var errorMessage: String? = null) {
+
+    companion object {
+        /**
+         * Creates [Resource] object with `SUCCESS` status and [data].
+         */
+        fun <ResultType> success(data: ResultType): Resource<ResultType> = Resource(Status.SUCCESS, data)
+
+        /**
+         * Creates [Resource] object with `LOADING` status to notify
+         * the UI to showing loading.
+         */
+        fun <ResultType> loading(): Resource<ResultType> = Resource(Status.LOADING)
+
+        /**
+         * Creates [Resource] object with `ERROR` status and [message].
+         */
+        fun <ResultType> error(message: String?): Resource<ResultType> = Resource(Status.ERROR, errorMessage = message)
+    }
+}

app/src/main/java/com/akshay/newsapp/model/Resource.kt

@@ -0,0 +1,24 @@
+package com.akshay.newsapp.model.network
+
+/**
+ * Status of a resource that is provided to the UI.
+ *
+ *
+ * These are usually created by the Repository classes where they return
+ * `LiveData<Resource<T>>` to pass back the latest data to the UI with its fetch status.
+ */
+enum class Status {
+    SUCCESS,
+    ERROR,
+    LOADING;
+
+    /**
+     * Returns `true` if the [Status] is success else `false`.
+     */
+    fun isSuccessful() = this == SUCCESS
+
+    /**
+     * Returns `true` if the [Status] is loading else `false`.
+     */
+    fun isLoading() = this == LOADING
+}