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 async jobs, plays the role like light-weight threads.
 
 [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://github.com/Kotlin/kotlinx.coroutines
 
 Upcoming features
 -----------------

app/build.gradle

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

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

@@ -16,23 +16,17 @@
 
 package com.google.samples.apps.sunflower.data
 
-import com.google.samples.apps.sunflower.utilities.runOnIoThread
-
 class GardenPlantingRepository private constructor(
     private val gardenPlantingDao: GardenPlantingDao
 ) {
 
     fun createGardenPlanting(plantId: String) {
-        runOnIoThread {
-            val gardenPlanting = GardenPlanting(plantId)
-            gardenPlantingDao.insertGardenPlanting(gardenPlanting)
-        }
+        val gardenPlanting = GardenPlanting(plantId)
+        gardenPlantingDao.insertGardenPlanting(gardenPlanting)
     }
 
     fun removeGardenPlanting(gardenPlanting: GardenPlanting) {
-        runOnIoThread {
-            gardenPlantingDao.deleteGardenPlanting(gardenPlanting)
-        }
+        gardenPlantingDao.deleteGardenPlanting(gardenPlanting)
     }
 
     fun getGardenPlantingForPlant(plantId: String) =

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

@@ -18,11 +18,12 @@ package com.google.samples.apps.sunflower.viewmodels
 
 import androidx.lifecycle.LiveData
 import androidx.lifecycle.Transformations
-import androidx.lifecycle.ViewModel
 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.Dispatchers.IO
+import kotlinx.coroutines.launch
 
 /**
  * The ViewModel used in [PlantDetailFragment].
@@ -31,7 +32,7 @@ class PlantDetailViewModel(
     plantRepository: PlantRepository,
     private val gardenPlantingRepository: GardenPlantingRepository,
     private val plantId: String
-) : ViewModel() {
+) : ScopedViewModel() {
 
     val isPlanted: LiveData<Boolean>
     val plant: LiveData<Plant>
@@ -48,7 +49,7 @@ class PlantDetailViewModel(
         plant = plantRepository.getPlant(plantId)
     }
 
-    fun addPlantToGarden() {
+    fun addPlantToGarden() = launch(IO) {
         gardenPlantingRepository.createGardenPlanting(plantId)
     }
 }

app/src/main/java/com/google/samples/apps/sunflower/utilities/AppExecutors.kt → app/src/main/java/com/google/samples/apps/sunflower/viewmodels/ScopedViewModel.kt

@@ -14,15 +14,21 @@
  * limitations under the License.
  */
 
-package com.google.samples.apps.sunflower.utilities
+package com.google.samples.apps.sunflower.viewmodels
 
-import java.util.concurrent.Executors
+import androidx.lifecycle.ViewModel
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlin.coroutines.CoroutineContext
 
-private val IO_EXECUTOR = Executors.newSingleThreadExecutor()
+abstract class ScopedViewModel : ViewModel(), CoroutineScope {
+    private val job = Job()
 
-/**
- * Utility method to run blocks on a dedicated background thread, used for io/database work.
- */
-fun runOnIoThread(f: () -> Unit) {
-    IO_EXECUTOR.execute(f)
+    override val coroutineContext: CoroutineContext
+        get() = Dispatchers.Main + job
+
+    override fun onCleared() {
+        job.cancel()
+    }
 }

build.gradle

@@ -25,6 +25,7 @@ buildscript {
         // App dependencies
         constraintLayoutVersion = '2.0.0-alpha2'
         coreTestingVersion = '2.0.0'
+        coroutines = "1.0.0"
         espressoVersion = '3.1.0-alpha4'
         glideVersion = '4.8.0'
         gradleVersion = '3.2.1'