版本2:如何将数据从后台服务/线程传递到除创建后台服务的MainActivity之外的其他活动

Question

我创建了一个简单的Android应用程序,用于测试如何使用处理程序或处理程序将数据从后台服务/线程传递到除创建后台服务的MainActivity之外的其他一些活动.我已经在MainActivity中使用了服务,线程和处理程序.最后一步是获取处理程序以将数据传递给除MainActivity之外的其他活动.我可以让服务将消息传递给MainActivity的处理程序,但我不知道如何让它将数据传递给其他一些活动.

为什么有人想要这样做？我认为这与一个简单的MP3播放器相比,但实际上它与一个不错的FM收音机相比.MainActivity使用后台服务,允许我选择FM电台.当我启动Play活动时,它应该绑定到相同的后台服务,这样我就可以继续听,而它(好的部分)显示音频的图形均衡器或动画.基本上,我不知道如何从多个活动绑定到后台服务.

我的代码最初基于Pro Android 2中的服务示例页面304,并且受到CommonsWare示例应用程序的极大帮助.

请查看我目前的代码.它由三个经过仔细评论的文件组成,这些文件描述了我正在尝试做的事情以及除了MainActivity之外我将数据传递给其他一些活动的困难:

/**************************************************************************************************
 * 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);

        Log.d(TAG, "starting service");

        /*
         * 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.
                Intent backgroundService = new Intent(MainActivity.this, com.marie.mainactivity.BackgroundService.class);
                backgroundService.putExtra(BackgroundService.EXTRA_MESSENGER, new Messenger(handler));
                startService(backgroundService);

                // Start the RcvMessages activity to receive messages from the handler. But how???
                Intent messages = new Intent(MainActivity.this, com.marie.mainactivity.RcvMessages.class);
                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 handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // simple handler test (does not send messages to RcvMessages activity
            String obj = (String) msg.obj;
            Log.i("handleMessge", "obj: " + obj);  
        }
    };
}

/**************************************************************************************************
 * 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;

/*
 * 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 = "com.marie.mainactivity.EXTRA_MESSENGER";
    private Messenger messenger;

    @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 class
            try {
                Message msg1 = Message.obtain();
                msg1.obj = "Hello 1";
                messenger.send(msg1);
            } catch (RemoteException e) {
                e.printStackTrace();
            }

            // 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();
    }

    /*
     * onStart is where we get our reference the Messenger that allows
     * us to send messages to the handler defined in the MainActivity class.
     */
    @Override
    public void onStart(Intent intent, int startId) {
        super.onStart(intent, startId);

        Bundle extras = intent.getExtras();
        messenger = (Messenger)extras.get(EXTRA_MESSENGER);
    }

    @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, 0, new Intent(this, MainActivity.class), 0);

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

        notificationMgr.notify(R.id.app_notification_id, 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.os.Bundle;
import android.text.InputType;
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 {

    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");
    }
}

除了创建backgraound服务的MainActivity之外,任何使用后台服务,线程和处理程序将数据传递给其他活动的帮助都将非常感激.

Answer 1

它Handler与特定的线程相关联,因此只要您在UI线程中创建它,您需要做的就是共享处理程序.我会把你的处理程序放在我的Application班级.Messenger如果你愿意,你可以把整个放在那里.然后你可以通过任何活动访问处理程序((MyApplication)getApplication()).getHandler().当活动开始或暂停时,您可以将其注册为回调.

所以这样的事情

public class MyApplication extends Application {
   Handler h = new Handler() {
      public void handleMessage(Message m) {
        if (realCallback!=null) {
           realCallback.handleMessage(m);
        }
      }
   };
   Handler.Callback realCallback=null;
   ......
   public Handler getHandler() {
      return h;
   }

   public void setCallback(Handler.Callback c) {
      realCallback = c;
   }
}

在任何需要通过信使接收请求的活动中

public class MyActivity extends Activity implements Handler.Callback

......

public void onStart() {
   ((MyApplication)getApplication()).setCallback(this);
}

public void onPause() {
   ((MyApplication)getApplication()).setCallback(null);
}

public void handleMessage(Message msg) {
  //.... Do stuff ....
}

}

这只是一个想法.您可能需要根据需要进行调整.

并且不要忘记MyApplication在AndroidManifest.xml中设置名称