NetworkObjectPool feature parity with the version in the Unity Multiplayer Samples Boss Room sample project (#176)

* Updating the NetworkObjectPool to have feature parity with the version in the Multiplayer Samples BossRoom project (it's now a NetworkBehaviour instead of a MonoBehaviour, uses the NetworkManager.Singleton, initializes the pool in OnNetworkSpawn, and it's a singleton)

* feature parity with the NetworkObjectPool in the Unity Multiplayer Samples Co-op Boss Room sample project.

Author: 11BelowStudio

com.community.netcode.extensions/Runtime/NetworkObjectPool/NetworkObjectPool.cs

@@ -7,10 +7,16 @@
 
 namespace Netcode.Extensions
 {
-    public class NetworkObjectPool : MonoBehaviour
+    /// <summary>
+    /// Object Pool for networked objects, used for controlling how objects are spawned by Netcode. Netcode by default will allocate new memory when spawning new
+    /// objects. With this Networked Pool, we're using custom spawning to reuse objects.
+    /// Hooks to NetworkManager's prefab handler to intercept object spawning and do custom actions
+    /// </summary>
+    public class NetworkObjectPool : NetworkBehaviour
     {
-        [SerializeField]
-        NetworkManager m_NetworkManager;
+        private static NetworkObjectPool _instance;
+
+        public static NetworkObjectPool Singleton=> _instance;
 
         [SerializeField]
         List<PoolConfigObject> PooledPrefabsList;
@@ -19,20 +25,65 @@ public class NetworkObjectPool : MonoBehaviour
 
         Dictionary<GameObject, Queue<NetworkObject>> pooledObjects = new Dictionary<GameObject, Queue<NetworkObject>>();
 
+        private bool m_HasInitialized = false;
+
         public void Awake()
+        {
+            if (_instance != null && _instance != this)
+            {
+                Destroy(this.gameObject);
+            }
+            else
+            {
+                _instance = this;
+            }
+        }
+
+        public override void OnNetworkSpawn()
         {
             InitializePool();
         }
 
+        public override void OnNetworkDespawn()
+        {
+            ClearPool();
+        }
+
+                public override void OnDestroy()
+        {
+            if (_instance == this)
+            {
+                _instance = null;
+            }
+            
+            base.OnDestroy();
+        }
+        
+
         public void OnValidate()
         {
             for (var i = 0; i < PooledPrefabsList.Count; i++)
             {
                 var prefab = PooledPrefabsList[i].Prefab;
                 if (prefab != null)
                 {
-                    Assert.IsNotNull(prefab.GetComponent<NetworkObject>(), $"{nameof(NetworkObjectPool)}: Pooled prefab \"{prefab.name}\" at index {i.ToString()} has no {nameof(NetworkObject)} component.");
+                    Assert.IsNotNull(
+                        prefab.GetComponent<NetworkObject>(),
+                        $"{nameof(NetworkObjectPool)}: Pooled prefab \"{prefab.name}\" at index {i.ToString()} has no {nameof(NetworkObject)} component."
+                    );
+
+                }
+
+                var prewarmCount = PooledPrefabsList[i].PrewarmCount;
+                if (prewarmCount < 0)
+                {
+                    Debug.LogWarning($"{nameof(NetworkObjectPool)}: Pooled prefab at index {i.ToString()} has a negative prewarm count! Making it not negative.");
+                    var thisPooledPrefab = PooledPrefabsList[i];
+                    thisPooledPrefab.PrewarmCount *= -1;
+                    PooledPrefabsList[i] = thisPooledPrefab;
                 }
+
+                
             }
         }
 
@@ -59,15 +110,12 @@ public NetworkObject GetNetworkObject(GameObject prefab, Vector3 position, Quate
         }
 
         /// <summary>
-        /// Return an object to the pool (and reset them).
+        /// Return an object to the pool (reset objects before returning).
         /// </summary>
         public void ReturnNetworkObject(NetworkObject networkObject, GameObject prefab)
         {
             var go = networkObject.gameObject;
-
-            // In this simple example pool we just disable objects while they are in the pool. But we could call a function on the object here for more flexibility.
             go.SetActive(false);
-            go.transform.SetParent(transform);
             pooledObjects[prefab].Enqueue(networkObject);
         }
 
@@ -95,15 +143,14 @@ private void RegisterPrefabInternal(GameObject prefab, int prewarmCount)
 
             var prefabQueue = new Queue<NetworkObject>();
             pooledObjects[prefab] = prefabQueue;
-
             for (int i = 0; i < prewarmCount; i++)
             {
                 var go = CreateInstance(prefab);
                 ReturnNetworkObject(go.GetComponent<NetworkObject>(), prefab);
             }
 
-            // Register netcode Spawn handlers
-            m_NetworkManager.PrefabHandler.AddHandler(prefab, new DummyPrefabInstanceHandler(prefab, this));
+            // Register Netcode Spawn handlers
+            NetworkManager.Singleton.PrefabHandler.AddHandler(prefab, new PooledPrefabInstanceHandler(prefab, this));
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -115,7 +162,7 @@ private GameObject CreateInstance(GameObject prefab)
         /// <summary>
         /// This matches the signature of <see cref="NetworkSpawnManager.SpawnHandlerDelegate"/>
         /// </summary>
-        /// <param name="prefabHash"></param>
+        /// <param name="prefab"></param>
         /// <param name="position"></param>
         /// <param name="rotation"></param>
         /// <returns></returns>
@@ -135,7 +182,6 @@ private NetworkObject GetNetworkObjectInternal(GameObject prefab, Vector3 positi
 
             // Here we must reverse the logic in ReturnNetworkObject.
             var go = networkObject.gameObject;
-            go.transform.SetParent(null);
             go.SetActive(true);
 
             go.transform.position = position;
@@ -147,12 +193,27 @@ private NetworkObject GetNetworkObjectInternal(GameObject prefab, Vector3 positi
         /// <summary>
         /// Registers all objects in <see cref="PooledPrefabsList"/> to the cache.
         /// </summary>
-        private void InitializePool()
+        public void InitializePool()
         {
+            if (m_HasInitialized) return;
             foreach (var configObject in PooledPrefabsList)
             {
                 RegisterPrefabInternal(configObject.Prefab, configObject.PrewarmCount);
             }
+            m_HasInitialized = true;
+        }
+
+        /// <summary>
+        /// Unregisters all objects in <see cref="PooledPrefabsList"/> from the cache.
+        /// </summary>
+        public void ClearPool()
+        {
+            foreach (var prefab in prefabs)
+            {
+                // Unregister Netcode Spawn handlers
+                NetworkManager.Singleton.PrefabHandler.RemoveHandler(prefab);
+            }
+            pooledObjects.Clear();
         }
     }
 
@@ -163,25 +224,28 @@ struct PoolConfigObject
         public int PrewarmCount;
     }
 
-    class DummyPrefabInstanceHandler : INetworkPrefabInstanceHandler
+    class PooledPrefabInstanceHandler : INetworkPrefabInstanceHandler
     {
         GameObject m_Prefab;
         NetworkObjectPool m_Pool;
 
-        public DummyPrefabInstanceHandler(GameObject prefab, NetworkObjectPool pool)
+        public PooledPrefabInstanceHandler(GameObject prefab, NetworkObjectPool pool)
         {
             m_Prefab = prefab;
             m_Pool = pool;
         }
 
-        public NetworkObject Instantiate(ulong ownerClientId, Vector3 position, Quaternion rotation)
+        NetworkObject INetworkPrefabInstanceHandler.Instantiate(ulong ownerClientId, Vector3 position, Quaternion rotation)
         {
-            return m_Pool.GetNetworkObject(m_Prefab, position, rotation);
+            var netObject = m_Pool.GetNetworkObject(m_Prefab, position, rotation);
+            return netObject;
         }
 
-        public void Destroy(NetworkObject networkObject)
+        void INetworkPrefabInstanceHandler.Destroy(NetworkObject networkObject)
         {
             m_Pool.ReturnNetworkObject(networkObject, m_Prefab);
         }
     }
+
+}
 }