Fetch OsuGameActivity through DI instead.

osu.Android/GameplayScreenRotationLocker.cs

@@ -13,6 +13,9 @@ namespace osu.Android
     {
         private Bindable<bool> localUserPlaying;
 
+        [Resolved]
+        private OsuGameActivity gameActivity { get; set; }
+
         [BackgroundDependencyLoader]
         private void load(OsuGame game)
         {
@@ -22,9 +25,9 @@ namespace osu.Android
 
         private void updateLock(ValueChangedEvent<bool> userPlaying)
         {
-            OsuGameActivity.Activity.RunOnUiThread(() =>
+            gameActivity.RunOnUiThread(() =>
             {
-                OsuGameActivity.Activity.RequestedOrientation = userPlaying.NewValue ? ScreenOrientation.Locked : ScreenOrientation.FullUser;
+                gameActivity.RequestedOrientation = userPlaying.NewValue ? ScreenOrientation.Locked : ScreenOrientation.FullUser;
             });
         }
     }

osu.Android/OsuGameActivity.cs

@@ -12,14 +12,10 @@ namespace osu.Android
     [Activity(Theme = "@android:style/Theme.NoTitleBar", MainLauncher = true, ScreenOrientation = ScreenOrientation.FullUser, SupportsPictureInPicture = false, ConfigurationChanges = ConfigChanges.Orientation | ConfigChanges.ScreenSize, HardwareAccelerated = false)]
     public class OsuGameActivity : AndroidGameActivity
     {
-        internal static Activity Activity { get; private set; }
-
-        protected override Framework.Game CreateGame() => new OsuGameAndroid();
+        protected override Framework.Game CreateGame() => new OsuGameAndroid(this);
 
         protected override void OnCreate(Bundle savedInstanceState)
         {
-            Activity = this;
-
             // The default current directory on android is '/'.
             // On some devices '/' maps to the app data directory. On others it maps to the root of the internal storage.
             // In order to have a consistent current directory on all devices the full path of the app data directory is set as the current directory.

osu.Android/OsuGameAndroid.cs

@@ -4,6 +4,7 @@
 using System;
 using Android.App;
 using Android.OS;
+using osu.Framework.Allocation;
 using osu.Game;
 using osu.Game.Updater;
 
@@ -11,6 +12,15 @@ namespace osu.Android
 {
     public class OsuGameAndroid : OsuGame
     {
+        [Cached]
+        private readonly OsuGameActivity gameActivity;
+
+        public OsuGameAndroid(OsuGameActivity activity)
+            : base(null)
+        {
+            gameActivity = activity;
+        }
+
         public override Version AssemblyVersion
         {
             get