How to pass Java object to C#?

Hey Everyone,

I am attempting to implement some Java native code into my Unity project, and I want to be able to use a function in my Java code that passes back an object based on a class defined within my java code to my C# Unity code. So far I have been unable to do this.

Here is an example of the JAVA side code:

Inventory:

 public List<Weapon> weapon;
 
 public List<Weapon> getWeaponFromInventory(Context context)
     {
         activity = (Activity)context;
         activity.runOnUiThread(new Runnable(){
             public void run()
             {
                 if(myInstance == null){
                      Log.e("Instance cannot be null");
                       throw new IllegalArgumentException("Instance was null when attempting to getWeaponFromInventory(context)");
                 }
                 weapon = instance.myInstance.getWeaponFromInventory(activity);
             }    
         });
         return weapon;
     }

I am then calling on this code from my C# in this way:

PlayerWeaponHandler:

 private static AndroidJavaObject instance;
         // Create link to java based Inventory
     private static AndroidJavaClass inventoryPlug= new AndroidJavaClass("com.myth.player.Inventory");
     //Create link to Unity Player
     public static AndroidJavaClass jc = new AndroidJavaClass("com.unity3d.player.UnityPlayer"); 
     //Get the current activity to use as context
     public static AndroidJavaObject currentAct = jc.GetStatic<AndroidJavaObject>("currentActivity");
     
     public static List<AndroidJavaObject> Weapon;
 
     static PlayerWeaponHandler(){
         if(Application.platform == RuntimePlatform.Android){
             Debug.Log ("PlayerWeaponHandler- Created");
             instance = inventoryPlug.CallStatic<AndroidJavaObject>("getInstance");
         }
     }
 
     public static void getWeapon(bool show){
         if(Application.platform == RuntimePlatform.Android){
              //Here I am attempting to call on a Java method that returns a Java Object holding the information about the 
             //players Weapon
             Weapon = instance.Call<List<AndroidJavaObject>>("getWeaponFromInventory", currentAct);
             return;
         }
         return;
     }

The error I get back is:

 I/Unity   (17813): JNI: Unknown signature for type 'System.Collections.Generic.List`1[UnityEngine.AndroidJavaObject]' (obj = System.Collections.Generic.List`1[UnityEngine.AndroidJavaObject]) equal
 
 I/Unity   (17813):  
 
 I/Unity   (17813): (Filename: ./Runtime/ExportGenerated/AndroidManaged/UnityEngineDebug.cpp Line: 43)
 
 I/Unity   (17813): 
 
 I/Unity   (17813): JNI: Unknown signature for type 'System.Collections.Generic.List`1[UnityEngine.AndroidJavaObject]' (obj = System.Collections.Generic.List`1[UnityEngine.AndroidJavaObject]) equal
 
 I/Unity   (17813):  
 
 I/Unity   (17813): (Filename: ./Runtime/ExportGenerated/AndroidManaged/UnityEngineDebug.cpp Line: 43)
 
 I/Unity   (17813): 
 
 E/Unity   (17813): getMethodID("getWeaponFromInventory", "(Lcom.unity3d.player.UnityPlayerNativeActivity;Z)") FAILED!
 
 D/dalvikvm(17813): GetMethodID: method not found: Lcom/myth/player/Inventory;.getWeaponFromInventory:(Lcom.unity3d.player.UnityPlayerNativeActivity;Z)
 
 I/Unity   (17813): JNI: Unable to find method id for 'getWeaponFromInventory'
 
 I/Unity   (17813):  
 
 I/Unity   (17813): (Filename: ./Runtime/ExportGenerated/AndroidManaged/UnityEngineDebug.cpp Line: 43)
 
 I/Unity   (17813): 
 
 I/Unity   (17813): JNI: Unknown return type 'System.Collections.Generic.List`1[UnityEngine.AndroidJavaObject]'
 
 I/Unity   (17813):  
 
 I/Unity   (17813): (Filename: ./Runtime/ExportGenerated/AndroidManaged/UnityEngineDebug.cpp Line: 43)

Has anyone ever dealt with trying to do this and found a way to make it work?

Would love to know if the Unity community has an answer to this question.