Spawning Prefab Instances¶

We need some code in our mod to load our prefab from our asset bundle and instantiate it in the game.

To demonstrate that our Asset Bundle is good, let's use Nautilus to spawn an instance of our new prefab when the player spawns.

1. In your existing MyFirstThunderKitMod project, open the MyFirstThunderKitModPlugin.cs file.

2. Add this code just under the existing const declarations:

   private const string MyGuid = "com.daftapplegames.myfirstthunderkitmod";
   private const string PluginName = "MyFirstThunderKitMod";
   private const string VersionString = "1.0.0";
   
   // *** Asset Bundle code here ***
   private const string AssetBundleName = "myfirstassetbundle";
   // Maintain a static reference to AssetBundle, so it can be used throughout your mod code
   public static AssetBundle MyAssetBundle { get; private set; }        
   

   Tip

   The Nautilus Asset Bundle API automatically looks in the "Assets" subfolder of your mod, so you only need to specify the bundle name.

3. Now add this code in the existing Awake method, just before the Logger.LogInfo($"Welcome to my first ThunderKit Plugin!"); line:

   ModLogger.LogInfo($"PluginName: {PluginName}, VersionString: {VersionString} is loaded.");
   
   // Use the Nautilus API to load the Asset Bundle
   ModLogger.LogInfo($"Loading AssetBundle from {AssetBundleName}...");
   MyAssetBundle =
      AssetBundleLoadingUtils.LoadFromAssetsFolder(Assembly.GetExecutingAssembly(), AssetBundleName);
   if (!MyAssetBundle)
   {
      ModLogger.LogInfo($"Failed to load AssetBundle from {AssetBundleName}! Check the path!");
   }
   ModLogger.LogInfo($"Asset Bundle Loaded!");
   
   ModLogger.LogInfo($"Welcome to my first ThunderKit Plugin!");
   

   This uses the Nautilus API to load the AssetBundle and stores a static reference to it that we can refer to elsewhere in our mod.

4. Now, create a new C# Script and call it PlayerPatches. Paste in this code:

   using HarmonyLib;
   using UnityEngine;
   
   namespace DaftAppleGames.MyFirstThunderKitMod
   {
      /// <summary>
      /// Class to implement Harmony patches on the Player class
      /// </summary>
      [HarmonyPatch(typeof(Player))]
      internal class PlayerPatches
      {
   
          // Postfix patch on the Awake method
          // Spawn a prefab instance when the player is spawned
          [HarmonyPatch(nameof(Player.Awake))]
          [HarmonyPostfix]
          public static void Awake_Postfix(Player __instance)
          {
              MyFirstThunderKitModPlugin.ModLogger.LogInfo($"Spawning Prefab instance...");
   
              // Get prefab from Asset Bundle then spawn an instance in front of the player
              GameObject myPrefab = MyFirstThunderKitModPlugin.MyAssetBundle.LoadAsset<GameObject>("MyFirstPrefab.prefab");
              MyFirstThunderKitModPlugin.ModLogger.LogInfo($"Found prefab in Asset Bundle. Creating instance...");
              GameObject newPrefabInstance = Object.Instantiate(myPrefab, __instance.transform, true);
   
              // Move the transform to 2 units in front of the player
              newPrefabInstance.transform.localPosition = Vector3.zero + __instance.transform.forward * 2;
   
              // Scale the instance - you could also set the scale in your prefab in Unity
              newPrefabInstance.transform.localScale = new Vector3(0.5f, 0.5f, 0.5f);
              newPrefabInstance.name = "MyNewPrefabInstance";
   
              MyFirstThunderKitModPlugin.ModLogger.LogInfo($"Prefab instance spawned!");
          }
      }
   }
   

   This Harmony patch code will fire when the player Game Object is spawned, and will load your new prefab from the asset bundle, instantiate an instance of it, and attach it just in front of the player.

   Tip

   You should always specify the file extension of the asset that you want to load, in this case .prefab. This avoids ambiguity in the case where you may have multiple assets of different types with the same name.

5. "Build and Deploy" the mod, with your new changes, and launch the game.

6. Load a saved game and you should see your rotating cube in front of you:

This just gives you an idea of how easy it is to create Asset Bundles and use them to introduce prefab instances into the game. Typically, you would not want to instantiate instances directly like this, and you should refer to the Nautilus documentation for adding new content into the game for details on how best to go about it.