Use viewModelScope instead of setting up own scope

Author: android-dev-lxl

RecyclerViewHeaders-Starter/app/build.gradle

@@ -63,6 +63,10 @@ dependencies {
     implementation 'androidx.legacy:legacy-support-v4:1.0.0'
     kapt "androidx.room:room-compiler:$room_version"
     implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"
+    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0"
+
+    // Kotlin Extensions and Coroutines support for Room
+    implementation "androidx.room:room-ktx:$room_version"
 
     // Coroutines
     implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$coroutine_version"

RecyclerViewHeaders-Starter/app/src/main/java/com/example/android/trackmysleepquality/database/SleepDatabaseDao.kt

@@ -31,7 +31,7 @@ import androidx.room.Update
 interface SleepDatabaseDao {
 
     @Insert
-    fun insert(night: SleepNight)
+    suspend fun insert(night: SleepNight)
 
     /**
      * When updating a row with a value already set in a column,
@@ -40,23 +40,23 @@ interface SleepDatabaseDao {
      * @param night new value to write
      */
     @Update
-    fun update(night: SleepNight)
+    suspend fun update(night: SleepNight)
 
     /**
      * Selects and returns the row that matches the supplied start time, which is our key.
      *
      * @param key startTimeMilli to match
      */
     @Query("SELECT * from daily_sleep_quality_table WHERE nightId = :key")
-    fun get(key: Long): SleepNight
+    suspend fun get(key: Long): SleepNight
 
     /**
      * Deletes all values from the table.
      *
      * This does not delete the table, only its contents.
      */
     @Query("DELETE FROM daily_sleep_quality_table")
-    fun clear()
+    suspend fun clear()
 
     /**
      * Selects and returns all rows in the table,
@@ -70,7 +70,7 @@ interface SleepDatabaseDao {
      * Selects and returns the latest night.
      */
     @Query("SELECT * FROM daily_sleep_quality_table ORDER BY nightId DESC LIMIT 1")
-    fun getTonight(): SleepNight?
+    suspend fun getTonight(): SleepNight?
 
     /**
      * Selects and returns the night with given nightId.

RecyclerViewHeaders-Starter/app/src/main/java/com/example/android/trackmysleepquality/sleepdetail/SleepDetailViewModel.kt

@@ -42,13 +42,6 @@ class SleepDetailViewModel(
      */
     val database = dataSource
 
-    /** Coroutine setup variables */
-
-    /**
-     * viewModelJob allows us to cancel all coroutines started by this ViewModel.
-     */
-    private val viewModelJob = Job()
-
     private val night: LiveData<SleepNight>
 
     fun getNight() = night
@@ -72,16 +65,6 @@ class SleepDetailViewModel(
     val navigateToSleepTracker: LiveData<Boolean?>
         get() = _navigateToSleepTracker
 
-    /**
-     * Cancels all coroutines when the ViewModel is cleared, to cleanup any pending work.
-     *
-     * onCleared() gets called when the ViewModel is destroyed.
-     */
-    override fun onCleared() {
-        super.onCleared()
-        viewModelJob.cancel()
-    }
-
     /**
      * Call this immediately after navigating to [SleepTrackerFragment]
      */

RecyclerViewHeaders-Starter/app/src/main/java/com/example/android/trackmysleepquality/sleepquality/SleepQualityViewModel.kt

@@ -19,12 +19,9 @@ package com.example.android.trackmysleepquality.sleepquality
 import androidx.lifecycle.LiveData
 import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
 import com.example.android.trackmysleepquality.database.SleepDatabaseDao
-import kotlinx.coroutines.CoroutineScope
-import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.Job
 import kotlinx.coroutines.launch
-import kotlinx.coroutines.withContext
 
 /**
  * ViewModel for SleepQualityFragment.
@@ -40,25 +37,6 @@ class SleepQualityViewModel(
      */
     val database = dataSource
 
-    /** Coroutine setup variables */
-
-    /**
-     * viewModelJob allows us to cancel all coroutines started by this ViewModel.
-     */
-    private val viewModelJob = Job()
-
-    /**
-     * A [CoroutineScope] keeps track of all coroutines started by this ViewModel.
-     *
-     * Because we pass it [viewModelJob], any coroutine started in this scope can be cancelled
-     * by calling `viewModelJob.cancel()`
-     *
-     * By default, all coroutines started in uiScope will launch in [Dispatchers.Main] which is
-     * the main thread on Android. This is a sensible default because most coroutines started by
-     * a [ViewModel] update the UI after performing some processing.
-     */
-    private val uiScope = CoroutineScope(Dispatchers.Main + viewModelJob)
-
     /**
      * Variable that tells the fragment whether it should navigate to [SleepTrackerFragment].
      *
@@ -73,16 +51,6 @@ class SleepQualityViewModel(
     val navigateToSleepTracker: LiveData<Boolean?>
         get() = _navigateToSleepTracker
 
-    /**
-     * Cancels all coroutines when the ViewModel is cleared, to cleanup any pending work.
-     *
-     * onCleared() gets called when the ViewModel is destroyed.
-     */
-    override fun onCleared() {
-        super.onCleared()
-        viewModelJob.cancel()
-    }
-
     /**
      * Call this immediately after navigating to [SleepTrackerFragment]
      */
@@ -96,14 +64,12 @@ class SleepQualityViewModel(
      * Then navigates back to the SleepTrackerFragment.
      */
     fun onSetSleepQuality(quality: Int) {
-        uiScope.launch {
+        viewModelScope.launch {
             // IO is a thread pool for running operations that access the disk, such as
             // our Room database.
-            withContext(Dispatchers.IO) {
-                val tonight = database.get(sleepNightKey)
-                tonight.sleepQuality = quality
-                database.update(tonight)
-            }
+            val tonight = database.get(sleepNightKey)
+            tonight.sleepQuality = quality
+            database.update(tonight)
 
             // Setting this state variable to true will alert the observer and trigger navigation.
             _navigateToSleepTracker.value = true

RecyclerViewHeaders-Starter/build.gradle

@@ -21,7 +21,7 @@ buildscript {
     ext {
         kotlin_version = '1.3.72'
         archLifecycleVersion = '1.1.1'
-        room_version = '2.2.0'
+        room_version = '2.2.5'
         coroutine_version = '1.3.7'
         gradleVersion = '4.0.1'
         navigationVersion = '1.0.0-alpha07'