Android：活动和服务之间的通信

Question

我对 Android 有点陌生，所以请帮助我理解这一点。 在从 android 开发者网站上阅读服务时，我发现这一段我无法举出一个例子：

如果服务不提供绑定，则使用 startService() 传递的意图是应用程序组件和服务之间唯一的通信方式。但是，如果您希望服务发回结果，则启动服务的客户端可以为广播创建 PendingIntent（使用 getBroadcast()）并将其传递给启动服务的 Intent 中的服务。然后服务可以使用广播来传递结果。

我知道还有其他方法可以将结果发送回活动，但我认为上面解释的逻辑比任何其他方法都简单。请通过示例帮助我理解这一点。

Answer 1

我们可以使用BroadcastReceiver 或ResultReceiver 来接收来自Service 的结果。这一次，我想指导你使用ResultReceiver：

首先，创建一个类以在您的活动中接收结果并扩展ResultReceiver：

private class MyReceiver extends ResultReceiver {
    public MyReceiver(Handler handler) {
        super(handler);
    }

    @Override
    protected void onReceiveResult(int resultCode, Bundle resultData) {
        super.onReceiveResult(resultCode, resultData);
        /*
        * We can get the type of data passed from Service to Activity:
        * int --> getInt("key")
        * String --> getString("key")
        * boolean --> getBoolean("key")
        * /
        if (resultCode == MyService.RUNNING) {
            String str = resultData.getString("dataStringKey"); // get information within the key, i.e. "dataString"
            myTextView.setText(str); // set the text to get the data received
        }

        if (resultCode == MyService.SERVICE_STOPPED) {
            // do something, such as get data received with the key
        }
    }
}

在你的Service：

public static final int RUNNING = 0;
public static final int SERVICE_DESTROYED = 1;
private ResultReceiver receiver;
private Bundle resultData;
private int status;

@Override
public void onCreate() {
    super.onCreate();
    resultData = new Bundle();
    status = RUNNING;
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    receiver = intent.getParcelableExtra("receiver");
    String dataFromActivity = intent.getStringExtra("text");
    /*
    * send result/information to activity, also we can put:
    * int --> putInt("key", value)
    * boolean --> putBoolean("key", value)
    * String --> putString("key", "My string.")
    * /
    resultData.putString("dataStringKey", "Hi, this is a String data.");
    receiver.send(status, resultData);

    return Service.START_NOT_STICKY;
}

@Override
public void onDestroy() {
    status = SERVICE_DESTROYED;
    receiver.send(status, resultData);
    super.onDestroy();
}

当你触发Service:

Intent intent = new Intent(MyActivity.this, MyService.class);
intent.putExtra("text", "Text to be passed to Service.");
intent.putExtra("receiver", new MyReceiver(new Handler()));
this.startService(intent);

Answer 2

使用Intent 将数据从您的Activity 发送到Service，并使用LocalBroadcastManager 将数据从您的Service 发送到Activity。

这是关于如何使用 LocalBroadcastManager 的example。

public class LocalBroadcastExampleActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.log_list);

        Button buttonStartService = (Button)findViewById(R.id.button_ok);
        buttonStartService.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                //Register MessageService in Manifest to work
                Intent intent = new Intent(LocalBroadcastExampleActivity.this, MessageService.class);
                 intent.putExtra("mydatakey", myString);  // <--- set data to send to service
                startService(new Intent(LocalBroadcastExampleActivity.this, MessageService.class));
            }
        });

    }

    @Override
    protected void onPause() {
        // Unregister since the activity is paused.
        LocalBroadcastManager.getInstance(this).unregisterReceiver(
                mMessageReceiver);
        super.onPause();
    }

    @Override
    protected void onResume() {
        // Register to receive messages.
        // We are registering an observer (mMessageReceiver) to receive Intents
        // with actions named "custom-event-name".
        LocalBroadcastManager.getInstance(this).registerReceiver(
                mMessageReceiver, new IntentFilter("custom-event-name"));
        super.onResume();
    }

    // Our handler for received Intents. This will be called whenever an Intent
    // with an action named "custom-event-name" is broadcasted.
    private BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            // TODO Auto-generated method stub
            // Get extra data included in the Intent
            String message = intent.getStringExtra("message");
            Log.d("receiver", "Got message: " + message);
        }
    };

    public class MessageService extends Service {

        @Override
        public IBinder onBind(Intent intent) {
            // TODO Auto-generated method stub
            return null;
        }

        @Override
        public int onStartCommand(Intent intent, int flags, int startId) {
            // TODO Auto-generated method stub
            String mydata = intent.getStringExtra("mydatakey"); // <--- retrieve data sent from Service
            sendMessage();
            return super.onStartCommand(intent, flags, startId);
        }

        // Send an Intent with an action named "custom-event-name". The Intent
        // sent should
        // be received by the ReceiverActivity.
        private void sendMessage() {
            Log.d("sender", "Broadcasting message");
            Intent intent = new Intent("custom-event-name");
            // You can also include some extra data.
            intent.putExtra("message", "This is my message!");
            LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
        }

    }

}

但就我而言，我更喜欢使用事件总线库，例如 EventBus、Otto，它们更易于使用且耗时更少。