Unify system service calls

Unify the calls to getSystemService to a custom function that uses the ContextCompat getSystemService instead of the clunky vanilla getSystemService code.

app/src/main/java/org/oxycblt/auxio/playback/system/AudioReactor.kt

@@ -4,12 +4,12 @@ import android.animation.ValueAnimator
 import android.content.Context
 import android.media.AudioManager
 import androidx.core.animation.addListener
-import androidx.core.content.ContextCompat
 import androidx.media.AudioFocusRequestCompat
 import androidx.media.AudioManagerCompat
 import com.google.android.exoplayer2.SimpleExoPlayer
 import org.oxycblt.auxio.playback.state.PlaybackStateManager
 import org.oxycblt.auxio.settings.SettingsManager
+import org.oxycblt.auxio.ui.getSystemServiceSafe
 
 /**
  * Object that manages the AudioFocus state.
@@ -20,9 +20,7 @@ class AudioReactor(
     context: Context,
     private val player: SimpleExoPlayer
 ) : AudioManager.OnAudioFocusChangeListener {
-    private val audioManager = ContextCompat.getSystemService(
-        context, AudioManager::class.java
-    ) ?: error("Cannot obtain AudioManager.")
+    private val audioManager = context.getSystemServiceSafe(AudioManager::class)
 
     private val settingsManager = SettingsManager.getInstance()
     private val playbackManager = PlaybackStateManager.getInstance()

app/src/main/java/org/oxycblt/auxio/playback/system/PlaybackNotification.kt

@@ -182,15 +182,14 @@ class PlaybackNotification private constructor(
         const val ACTION_EXIT = "ACTION_AUXIO_EXIT_" + BuildConfig.BUILD_TYPE
 
         /**
-         * Build a new instance of [PlaybackNotification] from a [context] and [mediaSession]
+         * Build a new instance of [PlaybackNotification].
          */
-        fun from(context: Context, mediaSession: MediaSessionCompat): PlaybackNotification {
+        fun from(
+            context: Context,
+            notificationManager: NotificationManager,
+            mediaSession: MediaSessionCompat
+        ): PlaybackNotification {
             if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
-                // Create the notification channel if required.
-                val notificationManager = context.getSystemService(
-                    Context.NOTIFICATION_SERVICE
-                ) as NotificationManager
-
                 val channel = NotificationChannel(
                     CHANNEL_ID, context.getString(R.string.info_channel_name),
                     NotificationManager.IMPORTANCE_DEFAULT

app/src/main/java/org/oxycblt/auxio/playback/system/PlaybackService.kt

@@ -43,6 +43,7 @@ import org.oxycblt.auxio.music.toURI
 import org.oxycblt.auxio.playback.state.LoopMode
 import org.oxycblt.auxio.playback.state.PlaybackStateManager
 import org.oxycblt.auxio.settings.SettingsManager
+import org.oxycblt.auxio.ui.getSystemServiceSafe
 
 /**
  * A service that manages the system-side aspects of playback, such as:
@@ -135,8 +136,8 @@ class PlaybackService : Service(), Player.EventListener, PlaybackStateManager.Ca
 
         // --- NOTIFICATION SETUP ---
 
-        notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
-        notification = PlaybackNotification.from(this, mediaSession)
+        notificationManager = getSystemServiceSafe(NotificationManager::class)
+        notification = PlaybackNotification.from(this, notificationManager, mediaSession)
 
         // --- PLAYBACKSTATEMANAGER SETUP ---
 

app/src/main/java/org/oxycblt/auxio/ui/InterfaceUtils.kt

@@ -27,6 +27,7 @@ import com.reddit.indicatorfastscroll.FastScrollItemIndicator
 import com.reddit.indicatorfastscroll.FastScrollerView
 import org.oxycblt.auxio.R
 import org.oxycblt.auxio.logE
+import kotlin.reflect.KClass
 
 // --- VIEW CONFIGURATION ---
 
@@ -79,6 +80,19 @@ fun Context.getPlural(@PluralsRes pluralsRes: Int, value: Int): String {
     return resources.getQuantityString(pluralsRes, value, value)
 }
 
+/**
+ * Convenience method for getting a system service without nullability issues.
+ * @param T The system service in question.
+ * @param serviceClass The service's kotlin class [Java class will be used in function call]
+ * @return The system service
+ * @throws IllegalStateException If the system service cannot be retrieved.
+ */
+fun <T : Any> Context.getSystemServiceSafe(serviceClass: KClass<T>): T {
+    return checkNotNull(ContextCompat.getSystemService(this, serviceClass.java)) {
+        "System service ${serviceClass.simpleName} could not be instantiated"
+    }
+}
+
 /**
  * Resolve a color.
  * @param context [Context] required
@@ -221,7 +235,7 @@ private fun isSystemBarOnBottom(activity: Activity): Boolean {
             }
         }
     } else {
-        (activity.getSystemService(Context.WINDOW_SERVICE) as WindowManager).apply {
+        (activity.getSystemServiceSafe(WindowManager::class)).apply {
             defaultDisplay.getRealSize(realPoint)
             defaultDisplay.getMetrics(metrics)