sometime need read apk file in unity, with out know file path

real_assets_file_with_jni.cs

    public static string ReadFileInAPK(string filepath) {

        //取得应用的Activity
        var activity = new AndroidJavaClass("com.unity3d.player.UnityPlayer").GetStatic<AndroidJavaObject>("currentActivity");
        //从Activity取得AssetManager实例
        var assetManager = activity.Call<AndroidJavaObject>("getAssets");

        //打开文件流
        var stream = assetManager.Call<AndroidJavaObject>("open", filepath);
        //获取文件长度
        var availableBytes = stream.Call<int>("available");

        //取得InputStream.read的MethodID
        var clsPtr = AndroidJNI.FindClass("java.io.InputStream");
        var METHOD_read = AndroidJNIHelper.GetMethodID(clsPtr, "read", "([B)I");

        //申请一个Java ByteArray对象句柄
        var byteArray = AndroidJNI.NewByteArray(availableBytes);
        //调用方法
        int readCount = AndroidJNI.CallIntMethod(stream.GetRawObject(), METHOD_read, new[] { new jvalue() { l = byteArray } });
        //从Java ByteArray中得到C# byte数组
        var bytes = AndroidJNI.FromByteArray(byteArray);
        //删除Java ByteArray对象句柄
        AndroidJNI.DeleteLocalRef(byteArray);
        //关闭文件流
        stream.Call("close");
        stream.Dispose();
        //返回结果
        return System.Text.Encoding.Default.GetString(bytes);
    }