如何将数据从一个包中的类发​​送到另一个包中的类？

Question

I have developed an Android app which opens up a Unity app which will then return to the Android app. I have created a plugin Java class MyPlugin which acts as a bridge between Android and Unity. Unity calls this method and passes in a float as a parameter. The plugin MyPlugin is in the package com.example.unity and is in the path unityLibrary/java.

How do I access this float from classes in my main package in app/java? Or send this data from MyPlugin to the other classes?

My project structure looks like this:

-app
 -java
  -com.company.package1
   -Android class files
-unityLibrary
 -java
  -com
   -example.unity
    -MyPlugin.java

I have tried using an intent but aren't sure exactly what to do. All the examples I have seen deal with everything being in the same package. This is what I tried. printText() is a method in MyPlugin which is called from Unity:

public void printText(float num)
    {
        surfaceArea = num;
        System.out.println("Text from Unity: "+num);

        Intent intent =  new Intent();
        intent.setAction(Intent.ACTION_SEND);
        intent.putExtra(Intent.EXTRA_TEXT, ""+num);
        intent.setType("text/plain");
        mainActivity.startActivity(intent);
    }

Update 16/07/2021: Following Rolland Costomarob's advice, I am now using a Broadcast sender and receiver. My plugin now looks like this:

package com.example.unity;

import android.app.Activity;
import android.content.Intent;
import android.util.Log;

public class MyPlugin {
    private static final MyPlugin ourInstance = new MyPlugin();

    private static final String LOGTAG = "AltGras";

    public static MyPlugin getInstance() { return ourInstance; }
    public static BroadcastSender mainActivity;
    public float surfaceArea ;

    private MyPlugin() {
        mainActivity = new BroadcastSender();
        Log.i(LOGTAG, "Created MyPlugin");
    }

    public void printText(float num)
    {
        surfaceArea = num;
        System.out.println("printText: Text from Unity: "+num);
        mainActivity.SendBroadcast(num);
    }
}

BroadcastSender.java:

package com.example.unity;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;


public class BroadcastSender extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        setContentView(R.layout.activity_main);
    }

    public void SendBroadcast(float surfaceArea){
        System.out.println("In MainActivityUnity.SendBroadcast");

        Intent intent = new Intent();
        if (intent == null)
        {
            System.out.println("SendBroadcast: intent is null");
        }
        if (this == null)
        {
            System.out.println("SendBroadcast: this is null");
        }
        intent.setAction("com.alternativegrass.alternativegrassapp.CUSTOM_SENDDATA_INTENT");
        System.out.println("SendBroadcast: intent = "+intent);
        intent.putExtra("com.alternativegrass.alternativegrassapp.EXTRA_SURFACEAREA", ""+surfaceArea);
        sendBroadcast(intent);
    }

}

I get the following error:

AndroidJavaException: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.content.Context.sendBroadcast(android.content.Intent)' on a null object reference
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.content.Context.sendBroadcast(android.content.Intent)' on a null object reference

The line it is complaining about is: sendBroadcast(intent);

Answer 1

please try with broadcast and receiver. intent can't use for the different app. so you need to send broadcast from one app, receive data with filter.

https://developer.android.com/guide/components/broadcasts https://www.tutorialspoint.com/android/android_broadcast_receivers.htm

for example

in your manifest file

<receiver android:name=".MyBroadcastReceiver"  android:exported="true">
    <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED"/>
        <action android:name="android.intent.action.INPUT_METHOD_CHANGED" />
    </intent-filter>
</receiver>

and define receiver

public class MyBroadcastReceiver extends BroadcastReceiver {
        private static final String TAG = "MyBroadcastReceiver";
        @Override
        public void onReceive(Context context, Intent intent) {
            StringBuilder sb = new StringBuilder();
            sb.append("Action: " + intent.getAction() + "\n");
            sb.append("URI: " + intent.toUri(Intent.URI_INTENT_SCHEME).toString() + "\n");
            String log = sb.toString();
            Log.d(TAG, log);
            Toast.makeText(context, log, Toast.LENGTH_LONG).show();
        }
    }

and register receiver

BroadcastReceiver br = new MyBroadcastReceiver();
IntentFilter filter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
    filter.addAction(Intent.ACTION_AIRPLANE_MODE_CHANGED);
    this.registerReceiver(br, filter);

send broadcast like this

Intent intent = new Intent();
intent.setAction("com.example.broadcast.MY_NOTIFICATION");
intent.putExtra("data", "Nothing to see here, move along.");
sendBroadcast(intent);

you will receive message.

Answer 2

this is sending part (first apk)

Handler handler = new Handler(){
        @Override
        public void handleMessage(@NonNull Message msg) {
            SendBroadcast();
            super.handleMessage(msg);
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        handler.sendEmptyMessage(0);
    }

    public void SendBroadcast(){
        Intent intent = new Intent();
        intent.setAction("com.example.broadcast.MY_NOTIFICATION");
        intent.putExtra("Value",109.3f);
        intent.putExtra("Message","Working well");
        Log.e("Broadcast","Send broadcast");
        sendBroadcast(intent);
        handler.sendEmptyMessageDelayed(0,10000);
    }

this broadcast data every 10 sec

and this is receive part (second apk)

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        BroadcastReceiver br = new MyBroadcastReceiver();
        IntentFilter filter = new IntentFilter();
        filter.addAction("com.example.broadcast.MY_NOTIFICATION");
        this.registerReceiver(br, filter);
    }

    public class MyBroadcastReceiver extends BroadcastReceiver {
        private static final String TAG = "MyBroadcastReceiver";
        @Override
        public void onReceive(Context context, Intent intent) {
            StringBuilder sb = new StringBuilder();
            sb.append("Action: " + intent.getAction() + "\n");
            sb.append("Message: " + intent.getStringExtra("Message") + "\n");
            sb.append("Value: "+ intent.getFloatExtra("Value",0.0f));
            String log = sb.toString();
            Log.e("Broadcast ","Received");
            Log.d(TAG, log);
            Toast.makeText(context, log, Toast.LENGTH_LONG).show();
        }
    }

and this is result log

2021-07-16 01:18:40.488 2337-2337/com.example.broadcastreceiver E/Broadcast: Received 2021-07-16 01:18:40.488 2337-2337/com.example.broadcastreceiver D/MyBroadcastReceiver: Action: com.example.broadcast.MY_NOTIFICATION Message: Working wellValue: 109.3