Unity android plugin classnotfoundexception

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Java

Android

speech

Unity2D

I created a Java plugin to include speech recognition in my Unity Android game. It is activated by touching a button onscreen, and when the button is released, the audio is processed. This feature isn't working, and checking the game logs I found I am getting a ClassNotFoundException related to the plugin's class.

My plugin is a JAR file located at Assets/Plugins/Android inside my Unity project. Here is the code that it contains:

package com.example.unityandroidplswork;

import android.content.Intent;
import android.app.Activity;
import android.speech.RecognizerIntent;
import android.speech.SpeechRecognizer;
import android.util.Log;

import java.util.ArrayList;


public class STTPlugin {
    private static final int REQUEST_CODE = 1234;
    private static final String TAG = "SpeechRecognitionPlugin";
    private Activity activity;
    private SpeechRecognizer speechRecognizer;
    private SpeechRecognitionResultListener resultListener;

    public STTPlugin(Activity activity) {

        this.activity = activity;
    }

    public void startSpeechRecognition(SpeechRecognitionResultListener listener) {
        if (SpeechRecognizer.isRecognitionAvailable(activity.getApplicationContext())) {
            resultListener = listener;
            if (speechRecognizer == null) {
                speechRecognizer = SpeechRecognizer.createSpeechRecognizer(activity.getApplicationContext());
            }
            Intent intent = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
            intent.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL, RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
            intent.putExtra(RecognizerIntent.EXTRA_MAX_RESULTS, 10);
            speechRecognizer.startListening(intent);
            Log.d(TAG, "Escuchando...");
        } else {
            Log.d(TAG, "Reconocimiento no disponible.");
        }

    }

    public void stopSpeechRecognition() {
        if (speechRecognizer != null) {
            speechRecognizer.stopListening();
        }
    }

    private String[] processRecognitionResults(ArrayList<String> results) {
        return results.toArray(new String[results.size()]);
    }

    public void handleActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_CODE && resultCode == Activity.RESULT_OK) {
            ArrayList<String> results = data.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS);
            if (resultListener != null) {
                String[] resultsArray = processRecognitionResults(results);
                resultListener.onResults(resultsArray);
            }
        }
    }

    public interface SpeechRecognitionResultListener {
        void onResults(String[] results);
    }


}

And the C# script from which I call the plugin:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System;
using UnityEngine.UI;
using TMPro;

public class SpeechRecog : MonoBehaviour
{

    private AndroidJavaObject speechRecPlugin;
    public TextMeshProUGUI textofresult;

    // Start is called before the first frame update
    void Start()
    {
        AndroidJavaObject activity = new AndroidJavaClass("com.unity3d.player.UnityPlayer").GetStatic<AndroidJavaObject>("currentActivity");
        speechRecPlugin = new AndroidJavaObject("com.example.unityandroidplswork.STTPlugin", activity);
    }

    public void StartSpeechRecognition() {
        AndroidJavaObject speechResultListener = new AndroidJavaObject("com.example.unityandroidplswork.STTPlugin$SpeechRecognitionResultListener", this);
     
        speechRecPlugin.Call("startSpeechRecognition", speechResultListener);
    }

    public void StopSpeechRecognition() {
        speechRecPlugin.Call("stopSpeechRecognition");
    }

    private void ProcessRecognitionResults(string[] results) {
        string recognizedtext = "";
        foreach(string result in results) {
            Debug.Log("Result: " + result);
            recognizedtext += result + " ";
        }
        textofresult.text = recognizedtext;
        //process here for sure
        //ProcessCommands(results)
    } 


    private class SpeechRecognitionResultListener : AndroidJavaProxy {

        private SpeechRecog plugin;

        public SpeechRecognitionResultListener(SpeechRecog plugin) : base("com.example.unityandroidplswork.STTPlugin$SpeechRecognitionResultListener") {
            this.plugin = plugin;
        }

        public void onResults(string[] results) {
            plugin.ProcessRecognitionResults(results);
        }
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

What I have tried:

I searched about this problem and I tried proposed solutions such as reimporting the plugin, changing its location, unchecking the release field in the publishing settings... But none of this has worked for me.