结构大修改，改成朴实无华的结构，不过度架构。能跑就行

Assets/Scripts/NBC/Asset/Runtime/Utils/StreamingAssetsUtil.cs

@@ -0,0 +1,44 @@
+using UnityEngine;
+
+namespace NBC.Asset
+{
+    public sealed class StreamingAssetsUtil
+    {
+#if UNITY_ANDROID && !UNITY_EDITOR
+	private static AndroidJavaClass _unityPlayerClass;
+	public static AndroidJavaClass UnityPlayerClass
+	{
+		get
+		{
+			if (_unityPlayerClass == null)
+				_unityPlayerClass = new UnityEngine.AndroidJavaClass("com.unity3d.player.UnityPlayer");
+			return _unityPlayerClass;
+		}
+	}
+
+	private static AndroidJavaObject _currentActivity;
+	public static AndroidJavaObject CurrentActivity
+	{
+		get
+		{
+			if (_currentActivity == null)
+				_currentActivity = UnityPlayerClass.GetStatic<AndroidJavaObject>("currentActivity");
+			return _currentActivity;
+		}
+	}
+
+	/// <summary>
+	/// 利用安卓原生接口查询内置文件是否存在
+	/// </summary>
+	public static bool FileExists(string filePath)
+	{
+		return CurrentActivity.Call<bool>("CheckAssetExist", filePath);
+	}
+#else
+        public static bool FileExists(string filePath)
+        {
+            return System.IO.File.Exists(System.IO.Path.Combine(Application.streamingAssetsPath, filePath));
+        }
+#endif
+    }
+}