PR adjust

Addressed by #235 (comment)

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

@@ -18,11 +18,14 @@ 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.CoroutineScope
 import kotlinx.coroutines.Dispatchers.IO
+import kotlinx.coroutines.Job
 import kotlinx.coroutines.launch
 
 /**
@@ -32,11 +35,34 @@ class PlantDetailViewModel(
     plantRepository: PlantRepository,
     private val gardenPlantingRepository: GardenPlantingRepository,
     private val plantId: String
-) : ScopedViewModel() {
+) : ViewModel() {
 
     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(IO + 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
@@ -49,7 +75,7 @@ class PlantDetailViewModel(
         plant = plantRepository.getPlant(plantId)
     }
 
-    fun addPlantToGarden() = launch(IO) {
+    fun addPlantToGarden() = viewModelScope.launch(IO) {
         gardenPlantingRepository.createGardenPlanting(plantId)
     }
 }