refactor: improve null-safety, remove unsafe field initializers, and clean up achievement checks

- CarMove.cs: Added null checks for _pgsController before checking sign-in status or updating leaderboards to prevent potential NullReferenceExceptions. Simplified duplicated _driveAchievementUnlocked assignments by extracting them from the conditional branches.
- GameData.cs: Moved unsafe Unity API calls (FindFirstObjectByType and GameObject.Find) out of the field initializers in the serializable GameData class to prevent exceptions during JSON deserialization. Implemented lazy on-demand initialization for PlayerController and background images, and removed a redundant .gameObject call.
- FriendsPageController.cs: Added null checks for localUser and localUser.friends before iterating the friends list. Replaced explicit array initializers to avoid referencing the deprecated IUserProfile type, resolving the compiler warning.

Author: sotash

trivialkart/trivialkart-unity/Assets/Scripts/Controller/Game/CarMove.cs

@@ -100,23 +100,20 @@ private void FixedUpdate()
 #if PLAY_GAMES_SERVICES
     private void CheckDistanceAchievement(float newDistance)
     {
-        if (newDistance >= ACHIEVEMENT_DRIVE_DISTANCE &&
+        if (_pgsController != null &&
+            newDistance >= ACHIEVEMENT_DRIVE_DISTANCE &&
             _pgsController.CurrentSignInStatus == PGSController.PgsSigninStatus.PgsSigninLoggedIn)
         {
             var achievementManager = _pgsController.AchievementManager;
             if (achievementManager != null)
             {
-                if (achievementManager.GetAchievementUnlocked(
+                if (!achievementManager.GetAchievementUnlocked(
                         PGSAchievementManager.TrivialKartAchievements.Tk_Achievement_Drive))
-                {
-                    _driveAchievementUnlocked = true;
-                }
-                else
                 {
                     achievementManager.UnlockAchievement(
                         PGSAchievementManager.TrivialKartAchievements.Tk_Achievement_Drive);
-                    _driveAchievementUnlocked = true;
                 }
+                _driveAchievementUnlocked = true;
             }
         }
     }
@@ -126,7 +123,10 @@ private void Update()
     {
 #if PLAY_GAMES_SERVICES
         // Checks to see if we are due to update the distance traveled leaderboard
-        _pgsController.UpdateLeaderboard();
+        if (_pgsController != null)
+        {
+            _pgsController.UpdateLeaderboard();
+        }
 #endif
         // Use keys to control menu/gameplay
         if (_garageAction.WasPressedThisFrame())

trivialkart/trivialkart-unity/Assets/Scripts/Controller/PGS/FriendsPageController.cs

@@ -178,15 +178,20 @@ private void LoadAdditionalFriends()
     // the string listing all the user's friends, comma-delimited
     private void AddFriendsFromList()
     {
-        foreach (var friend in PlayGamesPlatform.Instance.localUser.friends)
+        var localUser = PlayGamesPlatform.Instance.localUser;
+        if (localUser != null && localUser.friends != null)
         {
-            if (string.IsNullOrEmpty(_friendsList))
+            foreach (var friend in localUser.friends)
             {
-                _friendsList = friend.userName;
-            }
-            else
-            {
-                _friendsList += (", " + friend.userName);
+                if (friend == null) continue;
+                if (string.IsNullOrEmpty(_friendsList))
+                {
+                    _friendsList = friend.userName;
+                }
+                else
+                {
+                    _friendsList += (", " + friend.userName);
+                }
             }
         }
     }

trivialkart/trivialkart-unity/Assets/Scripts/Objects/GameData.cs

@@ -62,8 +62,8 @@ public class GameData
     private const int InitialCoinAmount = 20;
     private const int TotalCarCount = 4;
     private const int TotalBackgroundCount = 2;
-    private PlayerController _playerController = Object.FindFirstObjectByType<PlayerController>();
-    private GameObject _backgroundImages = GameObject.Find("Background/backGroundImages").gameObject;
+    private PlayerController _playerController;
+    private GameObject _backgroundImages;
 
 
     public GameData()
@@ -186,7 +186,11 @@ public bool CheckCarOwnership(CarList.Car car)
     public void UpdateCarInUse(CarList.Car targetCar)
     {
         carInUseName = targetCar.Name;
-        _playerController.UpdateCarInUse();
+        if (_playerController == null)
+        {
+            _playerController = Object.FindFirstObjectByType<PlayerController>();
+        }
+        _playerController?.UpdateCarInUse();
     }
 
     // Check if the user owns a specific background.
@@ -201,9 +205,17 @@ public void UpdateBackgroundInUse(BackgroundList.Background targetBackground)
     {
         backgroundInUseName = targetBackground.Name;
 
-        foreach (Transform background in _backgroundImages.transform)
+        if (_backgroundImages == null)
         {
-            background.gameObject.GetComponent<SpriteRenderer>().sprite = targetBackground.ImageSprite;
+            _backgroundImages = GameObject.Find("Background/backGroundImages");
+        }
+
+        if (_backgroundImages != null)
+        {
+            foreach (Transform background in _backgroundImages.transform)
+            {
+                background.gameObject.GetComponent<SpriteRenderer>().sprite = targetBackground.ImageSprite;
+            }
         }
     }