Use Kotlin Coroutines for IO executor

README.md

@@ -65,6 +65,7 @@ Libraries Used
   * [Layout][35] - Lay out widgets using different algorithms.
 * Third party
   * [Glide][90] for image loading
+  * [Kotlin Coroutines][91] for managing background threads with simplified code and reducing needs for callbacks
 
 [0]: https://developer.android.com/jetpack/foundation/
 [1]: https://developer.android.com/topic/libraries/support-library/packages#v7-appcompat
@@ -83,6 +84,7 @@ Libraries Used
 [34]: https://developer.android.com/guide/components/fragments
 [35]: https://developer.android.com/guide/topics/ui/declaring-layout
 [90]: https://bumptech.github.io/glide/
+[91]: https://kotlinlang.org/docs/reference/coroutines-overview.html
 
 Upcoming features
 -----------------

app/build.gradle

@@ -63,6 +63,8 @@ dependencies {
     implementation "com.google.android.material:material:$rootProject.materialVersion"
     implementation "com.google.code.gson:gson:$rootProject.gsonVersion"
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$rootProject.kotlinVersion"
+    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$rootProject.coroutinesVersion"
+    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$rootProject.coroutinesVersion"
 
     // Testing dependencies
     androidTestImplementation "androidx.arch.core:core-testing:$rootProject.coreTestingVersion"

app/proguard-rules.pro

@@ -23,3 +23,12 @@
 # If you keep the line number information, uncomment this to
 # hide the original source file name.
 #-renamesourcefileattribute SourceFile
+
+# ServiceLoader support
+-keepnames class kotlinx.coroutines.internal.MainDispatcherFactory {}
+-keepnames class kotlinx.coroutines.CoroutineExceptionHandler {}
+
+# Most of volatile fields are updated with AFU and should not be mangled
+-keepclassmembernames class kotlinx.** {
+    volatile <fields>;
+}

app/src/main/java/com/google/samples/apps/sunflower/data/GardenPlantingRepository.kt

@@ -16,21 +16,22 @@
 
 package com.google.samples.apps.sunflower.data
 
-import com.google.samples.apps.sunflower.utilities.runOnIoThread
+import kotlinx.coroutines.Dispatchers.IO
+import kotlinx.coroutines.withContext
 
 class GardenPlantingRepository private constructor(
     private val gardenPlantingDao: GardenPlantingDao
 ) {
 
-    fun createGardenPlanting(plantId: String) {
-        runOnIoThread {
+    suspend fun createGardenPlanting(plantId: String) {
+        withContext(IO) {
             val gardenPlanting = GardenPlanting(plantId)
             gardenPlantingDao.insertGardenPlanting(gardenPlanting)
         }
     }
 
-    fun removeGardenPlanting(gardenPlanting: GardenPlanting) {
-        runOnIoThread {
+    suspend fun removeGardenPlanting(gardenPlanting: GardenPlanting) {
+        withContext(IO) {
             gardenPlantingDao.deleteGardenPlanting(gardenPlanting)
         }
     }

app/src/main/java/com/google/samples/apps/sunflower/viewmodels/PlantDetailViewModel.kt

@@ -23,6 +23,10 @@ import com.google.samples.apps.sunflower.PlantDetailFragment
 import com.google.samples.apps.sunflower.data.GardenPlantingRepository
 import com.google.samples.apps.sunflower.data.Plant
 import com.google.samples.apps.sunflower.data.PlantRepository
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers.Main
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.launch
 
 /**
  * The ViewModel used in [PlantDetailFragment].
@@ -36,6 +40,29 @@ class PlantDetailViewModel(
     val isPlanted: LiveData<Boolean>
     val plant: LiveData<Plant>
 
+    /**
+     * This is the job for all coroutines started by this ViewModel.
+     *
+     * Cancelling this job will cancel all coroutines started by this ViewModel.
+     */
+    private val viewModelJob = Job()
+
+    /**
+     * This is the scope for all coroutines launched by [PlantDetailViewModel].
+     *
+     * Since we pass [viewModelJob], you can cancel all coroutines launched by [viewModelScope] by calling
+     * viewModelJob.cancel().  This is called in [onCleared].
+     */
+    private val viewModelScope = CoroutineScope(Main + viewModelJob)
+
+    /**
+     * Cancel all coroutines when the ViewModel is cleared.
+     */
+    override fun onCleared() {
+        super.onCleared()
+        viewModelJob.cancel()
+    }
+
     init {
 
         /* The getGardenPlantingForPlant method returns a LiveData from querying the database. The
@@ -49,6 +76,8 @@ class PlantDetailViewModel(
     }
 
     fun addPlantToGarden() {
-        gardenPlantingRepository.createGardenPlanting(plantId)
+        viewModelScope.launch {
+            gardenPlantingRepository.createGardenPlanting(plantId)
+        }
     }
 }

build.gradle

@@ -25,6 +25,7 @@ buildscript {
         // App dependencies
         constraintLayoutVersion = '2.0.0-alpha2'
         coreTestingVersion = '2.0.0'
+        coroutinesVersion = "1.0.1"
         espressoVersion = '3.1.0-alpha4'
         glideVersion = '4.8.0'
         gradleVersion = '3.2.1'