Optimize the scene unload logic.

优化场景卸载逻辑，在加载新的主场景的时候自动卸载已经加载的所有场景。

Assets/YooAsset/Runtime/AssetSystem/AssetSystem.cs

@@ -10,6 +10,7 @@ namespace YooAsset
 	{
 		private static readonly List<AssetBundleLoaderBase> _loaders = new List<AssetBundleLoaderBase>(1000);
 		private static readonly List<ProviderBase> _providers = new List<ProviderBase>(1000);
+		private static readonly Dictionary<string, SceneOperationHandle> _sceneHandles = new Dictionary<string, SceneOperationHandle>(100);
 
 		/// <summary>
 		/// 在编辑器下模拟运行
@@ -132,6 +133,14 @@ namespace YooAsset
 		/// </summary>
 		public static SceneOperationHandle LoadSceneAsync(string scenePath, LoadSceneMode sceneMode, bool activateOnLoad, int priority)
 		{
+			// 注意：场景句柄永远保持唯一
+			if (_sceneHandles.ContainsKey(scenePath))
+				return _sceneHandles[scenePath];
+
+			// 如果加载的是主场景，则卸载所有缓存的场景
+			if (sceneMode == LoadSceneMode.Single)
+				UnloadAllScene();
+
 			ProviderBase provider = TryGetProvider(scenePath);
 			if (provider == null)
 			{
@@ -141,7 +150,9 @@ namespace YooAsset
 					provider = new BundledSceneProvider(scenePath, sceneMode, activateOnLoad, priority);
 				_providers.Add(provider);
 			}
-			return provider.CreateHandle() as SceneOperationHandle;
+			var handle = provider.CreateHandle() as SceneOperationHandle;
+			_sceneHandles.Add(scenePath, handle);
+			return handle;
 		}
 
 		/// <summary>
@@ -179,6 +190,48 @@ namespace YooAsset
 		}
 
 
+		internal static void UnloadSubScene(ProviderBase provider)
+		{
+			string scenePath = provider.AssetPath;
+			if (_sceneHandles.ContainsKey(scenePath) == false)
+				throw new Exception("Should never get here !");
+
+			// 释放子场景句柄
+			_sceneHandles[scenePath].ReleaseInternal();
+			_sceneHandles.Remove(scenePath);
+
+			// 卸载未被使用的资源（包括场景）
+			AssetSystem.UnloadUnusedAssets();
+
+			// 检验子场景是否销毁
+			if (provider.IsDestroyed == false)
+			{
+				throw new Exception("Should never get here !");
+			}
+		}
+		internal static void UnloadAllScene()
+		{
+			// 释放所有场景句柄
+			foreach (var valuePair in _sceneHandles)
+			{
+				valuePair.Value.ReleaseInternal();
+			}
+			_sceneHandles.Clear();
+
+			// 卸载未被使用的资源（包括场景）
+			AssetSystem.UnloadUnusedAssets();
+
+			// 检验所有场景是否销毁
+			foreach (var provider in _providers)
+			{
+				if (provider.IsSceneProvider())
+				{
+					if (provider.IsDestroyed == false)
+						throw new Exception("Should never get here !");
+				}
+			}
+		}
+
 		internal static AssetBundleLoaderBase CreateOwnerAssetBundleLoader(string assetPath)
 		{
 			string bundleName = BundleServices.GetBundleName(assetPath);
@@ -254,6 +307,7 @@ namespace YooAsset
 			return provider;
 		}
 
+
 		#region 调试专属方法
 		internal static void GetDebugReport(DebugReport report)
 		{

Assets/YooAsset/Runtime/AssetSystem/Handles/AssetOperationHandle.cs

@@ -2,7 +2,7 @@
 
 namespace YooAsset
 {
-	public class AssetOperationHandle : OperationHandleBase
+	public sealed class AssetOperationHandle : OperationHandleBase
 	{
 		private System.Action<AssetOperationHandle> _callback;
 

Assets/YooAsset/Runtime/AssetSystem/Handles/OperationHandleBase.cs

@@ -4,11 +4,13 @@ namespace YooAsset
 {
 	public abstract class OperationHandleBase : IEnumerator
 	{
+		private readonly string _cachedAssetPath;
 		internal ProviderBase _provider { private set; get; }
-		
+
 		internal OperationHandleBase(ProviderBase provider)
 		{
 			_provider = provider;
+			_cachedAssetPath = provider.AssetPath;
 		}
 		internal abstract void InvokeCallback();
 
@@ -63,7 +65,18 @@ namespace YooAsset
 		{
 			get
 			{
-				return _provider != null && _provider.IsDestroyed == false;
+				if (_provider != null && _provider.IsDestroyed == false)
+				{
+					return true;
+				}
+				else
+				{
+					if (_provider == null)
+						YooLogger.Warning($"Operation handle is released : {_cachedAssetPath}");
+					else if (_provider.IsDestroyed)
+						YooLogger.Warning($"Provider is destroyed : {_cachedAssetPath}");
+					return false;
+				}
 			}
 		}
 

Assets/YooAsset/Runtime/AssetSystem/Handles/SceneOperationHandle.cs

@@ -69,10 +69,35 @@ namespace YooAsset
 		}
 
 		/// <summary>
-		/// 异步卸载场景
+		/// 是否为主场景
+		/// </summary>
+		public bool IsMainScene()
+		{
+			if (IsValid == false)
+				return false;
+
+			if (_provider is DatabaseSceneProvider)
+			{
+				var temp = _provider as DatabaseSceneProvider;
+				return temp.SceneMode == LoadSceneMode.Single;
+			}
+			else if (_provider is BundledSceneProvider)
+			{
+				var temp = _provider as BundledSceneProvider;
+				return temp.SceneMode == LoadSceneMode.Single;
+			}
+			else
+			{
+				throw new System.NotImplementedException();
+			}
+		}
+
+		/// <summary>
+		/// 异步卸载子场景
 		/// </summary>
 		public UnloadSceneOperation UnloadAsync()
 		{
+			// 如果句柄无效
 			if (IsValid == false)
 			{
 				string error = $"{nameof(SceneOperationHandle)} is invalid.";
@@ -81,54 +106,23 @@ namespace YooAsset
 				return operation;
 			}
 
-			ProviderBase provider = _provider;
-
-			// 释放场景句柄
-			ReleaseInternal();
-
-			// 卸载未被使用的资源（包括场景）
-			AssetSystem.UnloadUnusedAssets();
-
-			// 返回场景卸载异步操作类
-			if (provider.IsDestroyed == false)
+			// 如果是主场景
+			if (IsMainScene())
 			{
-				YooLogger.Warning($"Scene can not unload. The provider not destroyed : {provider.AssetPath}");
-				var operation = new UnloadSceneOperation();
+				string error = $"Cannot unload main scene. Use {nameof(YooAssets.LoadSceneAsync)} method to change the main scene !";
+				YooLogger.Error(error);
+				var operation = new UnloadSceneOperation(error);
 				OperationSystem.ProcessOperaiton(operation);
 				return operation;
 			}
-			else
-			{
-				if (IsAdditiveScene(provider))
-				{
-					var operation = new UnloadSceneOperation(provider.SceneObject);
-					OperationSystem.ProcessOperaiton(operation);
-					return operation;
-				}
-				else
-				{
-					var operation = new UnloadSceneOperation();
-					OperationSystem.ProcessOperaiton(operation);
-					return operation;
-				}
-			}
-		}
 
-		private bool IsAdditiveScene(ProviderBase provider)
-		{
-			if (provider is DatabaseSceneProvider)
+			// 卸载子场景
+			Scene sceneObject = SceneObject;
+			AssetSystem.UnloadSubScene(_provider);
 			{
-				var temp = provider as DatabaseSceneProvider;
-				return temp.SceneMode == LoadSceneMode.Additive;
-			}
-			else if (provider is BundledSceneProvider)
-			{
-				var temp = provider as BundledSceneProvider;
-				return temp.SceneMode == LoadSceneMode.Additive;
-			}
-			else
-			{
-				throw new System.NotImplementedException();
+				var operation = new UnloadSceneOperation(sceneObject);
+				OperationSystem.ProcessOperaiton(operation);
+				return operation;
 			}
 		}
 	}

Assets/YooAsset/Runtime/AssetSystem/Handles/SubAssetsOperationHandle.cs

@@ -1,7 +1,7 @@
 
 namespace YooAsset
 {
-	public class SubAssetsOperationHandle : OperationHandleBase
+	public sealed class SubAssetsOperationHandle : OperationHandleBase
 	{
 		private System.Action<SubAssetsOperationHandle> _callback;
 

Assets/YooAsset/Runtime/AssetSystem/Operations/InstantiateOperation.cs

@@ -48,12 +48,15 @@ namespace YooAsset
 					_steps = ESteps.Done;
 					Status = EOperationStatus.Failed;
 					Error = $"{nameof(AssetOperationHandle)} is invalid.";
+					return;
 				}
+
 				if (_handle.AssetObject == null)
 				{
 					_steps = ESteps.Done;
 					Status = EOperationStatus.Failed;
 					Error = $"{nameof(AssetOperationHandle.AssetObject)} is null.";
+					return;
 				}
 
 				if(_setPositionRotation)

Assets/YooAsset/Runtime/AssetSystem/Operations/UnloadSceneOperation.cs

@@ -12,7 +12,6 @@ namespace YooAsset
 		{
 			Normal,
 			Error,
-			Skip,
 		}
 		private enum ESteps
 		{
@@ -40,10 +39,6 @@ namespace YooAsset
 			}
 		}
 
-		internal UnloadSceneOperation()
-		{
-			_flag = EFlag.Skip;
-		}
 		internal UnloadSceneOperation(string error)
 		{
 			_flag = EFlag.Error;
@@ -60,11 +55,6 @@ namespace YooAsset
 			{
 				_steps = ESteps.UnLoad;
 			}
-			else if (_flag == EFlag.Skip)
-			{
-				_steps = ESteps.Done;
-				Status = EOperationStatus.Succeed;
-			}
 			else if (_flag == EFlag.Error)
 			{
 				_steps = ESteps.Done;