一个以上的活动开始/绑定到服务

编程问答 2022-04-26

问题描述

| 根据我对服务的了解，我应该能够将多个活动绑定到同一个服务，但是它不起作用。为此，我的BackgroundService扩展了Service。 从我的MainActivity中，如下启动服务： 
Intent backgroundService = new Intent(MainActivity.this,BackgroundService.class);
backgroundService.putExtra(BackgroundService.EXTRA_MESSENGER_MAINACTIVITY,new Messenger(mainHandler));
startService(backgroundService);
然后从另一个活动中，我尝试如下绑定此相同的服务： 
Intent backgroundService = new Intent(RcvMessages.this,BackgroundService.class);
backgroundService.putExtra(BackgroundService.EXTRA_MESSENGER_RCVMESSAGES,new Messenger(rcvHandler));
startService(backgroundService);
我的理解是，与服务的每个绑定都将具有如上所述的自己的处理程序。但这是行不通的。只有第一个处理程序起作用。我究竟做错了什么？ @Femi说\“您正在将Messenger作为Intent额外传递给BackgroundService类，但是没有内置的Android代码可以理解如何处理该Messenger：这必须由BackgroundService实现提供。 BackgroundService的代码，以及它与传递的M​​essenger实例有什么关系？\“ @ Femi看看我的BackgroundSerive，尤其是onStartCommand（）： 
/**************************************************************************************************
 * File: BackgroundService.java
 * Application: BackgroundService
 * Description: This file contains the background Service that is launched by the MainActivity\'s
 *     bind button.
 **************************************************************************************************/

package com.marie.mainactivity;

import android.app.Notification;
import android.app.notificationmanager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.os.Bundle;
import android.os.IBinder;
import android.os.Message;
import android.os.Messenger;
import android.os.remoteexception;
import android.util.Log;

/*
 * Class: BackgroundService
 * Purpose: Using the onStart() method the BackgroundService gets the reference to the
 *     Messenger instance that was passed to BackgroundService. The messenger is then
 *     used by the ServiceWorker() thread to send messages to the handler that is defined
 *     in the MainActivity class.
 */
public class BackgroundService extends Service {
    private notificationmanager notificationMgr;

    public static final String EXTRA_MESSENGER_MAINACTIVITY = \"com.marie.mainactivity.EXTRA_MESSENGER_MAINACTIVITY\";
    private Messenger messenger_mainactivity;

    public static final String EXTRA_MESSENGER_RCVMESSAGES = \"com.marie.mainactivity.EXTRA_MESSENGER_RCVMESSAGES\";
    private Messenger messenger_rcvmessages;

    public static final String EXTRA_SONG = \"com.marie.mainactivity.EXTRA_SONG\";
    int song = 0;

    @Override
    public void onCreate() {
        super.onCreate();

        notificationMgr = (notificationmanager)getSystemService(NOTIFICATION_SERVICE);

        displayNotificationMessage(\"starting Background Service\");

        Thread thr = new Thread(null,new ServiceWorker(),\"BackgroundService\");
        thr.start();
    }   

    /*
     * This is the ServiceWorker thread that passes messages to the handler defined in
     * the MainActivity class.
     * NOTE: Instead of passing messages to a handler in MainActivity I would like
     * it to pass messages to a handler defined in the RcvMessages activity.
     */
    class ServiceWorker implements Runnable
    {
        public void run() {
            // do background processing here... something simple

            // send a message to the handler defined in the MainActivity activity
            if (messenger_mainactivity != null)
            {
                try {
                    Message msg1 = Message.obtain();
                    msg1.obj = \"SongData\";
                    msg1.arg1 = 1000;
                    messenger_mainactivity.send(msg1);
                } catch (remoteexception e) {
                    e.printstacktrace();
                } catch (NullPointerException e) {
                    e.printstacktrace();
                }
            } else {
                Log.e(\"messenger_mainactivity\",\"null\");
            }

            // send a message to the handler defined in the RcvMessages activity
            if (messenger_rcvmessages != null)
            {
                try {
                    Message msg1 = Message.obtain();
                    msg1.obj = \"Song\";
                    msg1.arg1 = song;
                    messenger_rcvmessages.send(msg1);
                } catch (remoteexception e) {
                    e.printstacktrace();
                } catch (NullPointerException e) {
                    e.printstacktrace();
                }
            } else {
                Log.e(\"messenger_rcvmessages\",\"null\");
            }

            // stop the service when done...
            // BackgroundService.this.stopSelf();
            // Or use the unbindBtn in the MainActivity class.
        }
    }

    @Override
    public void onDestroy()
    {
        displayNotificationMessage(\"stopping Background Service\");
        super.onDestroy();
    }

    /*
    @Override
    public void onStart(Intent intent,int startId) {
        super.onStart(intent,startId);
    }
    */

    @Override
    public int onStartCommand(Intent intent,int flags,int startId) {
        super.onStartCommand(intent,flags,startId);

        Bundle extras = intent.getExtras();
        Messenger messenger;

        messenger = (Messenger)extras.get(EXTRA_MESSENGER_MAINACTIVITY);
        if (messenger != null) {
            messenger_mainactivity = messenger;
        }

        messenger = (Messenger)extras.get(EXTRA_MESSENGER_RCVMESSAGES);
        if (messenger != null) {
            messenger_rcvmessages = messenger;
            song = extras.getInt(EXTRA_SONG);
        }

        return START_NOT_STICKY;
    }

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    private void displayNotificationMessage(String message)
    {
        Notification notification = new Notification(R.drawable.note,message,System.currentTimeMillis());

        PendingIntent contentIntent = PendingIntent.getActivity(this,new Intent(this,MainActivity.class),0);

        notification.setLatestEventInfo(this,\"Background Service\",contentIntent);

        notificationMgr.notify(R.id.app_notification_id,notification);
    }
}
这是整个代码： 
/**************************************************************************************************
 * File: MainActivity.java
 * Application: BackgroundService
 * Description: This file contains the main activity that is run when the BackgroundService
 *     application is launched.
 **************************************************************************************************/

package com.marie.mainactivity;

import com.marie.mainactivity.BackgroundService;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.Messenger;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

/*
 * Class: MainActivity
 * Purpose: Using a button,the MainActivity class starts the backgroundService and
 *     the RcvMessages activity. Using another button MainActivity stops the backgroundService.
 *     NOTE: RcvMessages is only a stub that does nothing but display a simple message.
 * Handler: MainActivity defines and provides a reference to \"handler\" for the backgroundService.
 */
public class MainActivity extends Activity {
    private static final String TAG = \"MainActivity\";

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        /*
         * The bind button: bindBtn
         * Clicking this button starts the background Service and launches the
         * RcvMessages activity. NOTE: RcvMessages is only a stub so far.
         */
        Button bindBtn = (Button)findViewById(R.id.bindBtn);
        bindBtn.setonClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // Start the background Service for sending canned messages to the handler as a test.
                Log.d(TAG,\"starting service\");
                Intent backgroundService = new Intent(MainActivity.this,BackgroundService.class);
                backgroundService.putExtra(BackgroundService.EXTRA_MESSENGER_MAINACTIVITY,new Messenger(mainHandler));
                startService(backgroundService);

                // Start the RcvMessages activity to receive messages from the handler. But how???
                Intent messages = new Intent(MainActivity.this,RcvMessages.class);
                messages.putExtra(RcvMessages.EXTRA_SONG,10);
                startActivity(messages);
            }
        });

        /*
         * The unbind button: unbindBtn
         * Clicking this button stops the background Service.
         */
        Button unbindBtn = (Button)findViewById(R.id.unbindBtn);
        unbindBtn.setonClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {

                // Stop the background Service
                Intent backgroundService = new Intent(MainActivity.this,BackgroundService.class);
                stopService(backgroundService);
            }
        });
    }

    /*
     * This is the handler to be passed to the background Service via a Messenger.
     * NOTE: I want it to send messages to my RcvMessages activity.
     */
    private Handler mainHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // simple handler test (does not send messages to RcvMessages activity
            String obj = (String) msg.obj;
            int arg1 = msg.arg1;
            Log.i(\"handleMessge_mainactivity\",\"obj: \" + obj + \" \" + \"arg1: \" + arg1);  
        }
    };
}


/**************************************************************************************************
 * File: BackgroundService.java
 * Application: BackgroundService
 * Description: This file contains the background Service that is launched by the MainActivity\'s
 *     bind button.
 **************************************************************************************************/

package com.marie.mainactivity;

import android.app.Notification;
import android.app.notificationmanager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.os.Bundle;
import android.os.IBinder;
import android.os.Message;
import android.os.Messenger;
import android.os.remoteexception;
import android.util.Log;

/*
 * Class: BackgroundService
 * Purpose: Using the onStart() method the BackgroundService gets the reference to the
 *     Messenger instance that was passed to BackgroundService. The messenger is then
 *     used by the ServiceWorker() thread to send messages to the handler that is defined
 *     in the MainActivity class.
 */
public class BackgroundService extends Service {
    private notificationmanager notificationMgr;

    public static final String EXTRA_MESSENGER_MAINACTIVITY = \"com.marie.mainactivity.EXTRA_MESSENGER_MAINACTIVITY\";
    private Messenger messenger_mainactivity;

    public static final String EXTRA_MESSENGER_RCVMESSAGES = \"com.marie.mainactivity.EXTRA_MESSENGER_RCVMESSAGES\";
    private Messenger messenger_rcvmessages;

    public static final String EXTRA_SONG = \"com.marie.mainactivity.EXTRA_SONG\";
    int song = 0;

    @Override
    public void onCreate() {
        super.onCreate();

        notificationMgr = (notificationmanager)getSystemService(NOTIFICATION_SERVICE);

        displayNotificationMessage(\"starting Background Service\");

        Thread thr = new Thread(null,notification);
    }
}


/**************************************************************************************************
 * File: RcvMessages.java
 * Application: BackgroundService
 * Description: This file contains stub code that displays a test message in an EditText.
 **************************************************************************************************/

package com.marie.mainactivity;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.Messenger;
import android.text.InputType;
import android.util.Log;
import android.widget.EditText;

/*
 * Class: RcvMessages
 * Purpose: RcvMessages is stub code that I want to extend in some way to receive messages from
 *     the background Service.
 *     NOTE: I don\'t kNow who to do this.
 */
public class RcvMessages extends Activity {

    public static final String EXTRA_SONG = \"com.marie.mainactivity.EXTRA_SONG\";
    EditText myText;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.messages);

        myText = (EditText)findViewById(R.id.my_text);

        myText.setSingleLine();
        myText.setInputType(InputType.TYPE_NULL);

        // display a simple test message for Now.
        // myText.setText(\"RcvMessages here\");
    }

    @Override
    public void onStart(){
        super.onStart();
        Bundle extras = getIntent().getExtras();
        int song = (Integer) extras.get(EXTRA_SONG);
        //myText.setText(\"song \" + song);

        // Start the background Service for sending canned messages to the handler as a test.
        Intent backgroundService = new Intent(RcvMessages.this,BackgroundService.class);
        backgroundService.putExtra(BackgroundService.EXTRA_MESSENGER_RCVMESSAGES,new Messenger(rcvHandler));
        backgroundService.putExtra(BackgroundService.EXTRA_SONG,song);
        bindService(backgroundService);
    }

    private void bindService(Intent backgroundService) {
        // Todo Auto-generated method stub

    }

    @Override
    public void onStop() {
        super.onStop();
        myText.setText(\"\");
    }

    /*
     * This is the handler to be passed to the background Service via a Messenger.
     * NOTE: I want it to send messages to my RcvMessages activity.
     */
    private Handler rcvHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // simple handler test
            String song = (String) msg.obj;
            int songNum = msg.arg1;
            Log.i(\"handleMessage_rcvmessages\",\"songNum: \" + songNum);  

            myText.setText(song + \" \" + songNum);
        }
    };

}
    

解决方法

        您没有绑定到尝试启动服务的服务（使用bindService完成）。如果要绑定，则应使用bindService并从javadoc和指定的链接中读取该行为。 至于独立的ѭ4不能正常工作：取决于ѭ5的实现。     ,        我可以像这样将活动成功绑定到我的服务： 
bindService(new Intent(Binding.this,LocalService.class),mConnection,Context.BIND_AUTO_CREATE);
    
一个以上服务服务活动活动绑定绑定