android - 从另一个应用程序绑定(bind)到服务

Question

我写了两个应用程序(目标 Gingerbread )。比方说 app1 和 app2。 App1 有两个以“BOOT_COMPLETED”开始的服务，它们以返回值 START_STICKY 开始。它们在不同的线程中运行。使长话短说。其中一项服务正在监视串行端口上的传入数据(一种应用程序与串行端口另一端接口(interface)通信的代理)。另一个有一个监听器来监视一些系统状态并等待来自其他应用程序的一些“指令”。我知道它们运行良好，因为它们列在正在运行的服务中，并且我添加了一些代码，当某些特定数据来自串行端口时，它们会强制它们执行某些操作。

现在的问题是:我写了 app2。它尝试绑定(bind)到 app1 中的一项服务。我用了android-developper文档并在 app1 和 app2 中的服务之间实现了双向通信。因为我只有少量非常简单的数据要发送，所以我按照建议使用了一个信使。我基本上只使用“什么，arg1 和 arg2”我没有使用文档建议的 AIDL 接口(interface)。

这是在 app1 中声明服务的 androidmanifest 部分，我也尝试绑定(bind)。

    <service android:name=".ModemWatcherService"
              android:label="@string/app_name"
              android:exported="true">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
            <!-- Service name -->
            <action android:name="com.admetric.modemwatcher.Service" />
        </intent-filter>
    </service>

那么，下面是app1中处理这个问题的几种方法:

    @Override
public IBinder onBind(Intent intent) {
    Log.d(TAG, "entering onBind");
    return mMessenger.getBinder();
}

/**
 * Handler of incoming messages from clients.
 */
class IncomingHandler extends Handler {
    @Override
    public void handleMessage(Message msg) {
        String logMessage = "Received meaasge what= %d, arg1= %d, arg2= %d" + String.valueOf(msg.what) + String.valueOf(msg.arg1) + String.valueOf( msg.arg2);
        Log.d(TAG, logMessage);
        switch (msg.what) {
            case MSG_REGISTER_CLIENT:
                mClients.add(msg.replyTo);
                break;
            case MSG_UNREGISTER_CLIENT:
                mClients.remove(msg.replyTo);
                break;
            case .....  
             more code here for the application
            default:
                super.handleMessage(msg);
        }
    }
}


@Override
public void onCreate() {
    mHandler = new Handler();
    startSignalLevelListener();
    Log.i(TAG, "Just did onCreated");
    // Display a notification about us starting.  We put an icon in the status bar.
    // showNotification();
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    Log.i(TAG, "Received start id " + startId + ": " + intent);
    // We want this service to continue running until it is explicitly
    // stopped, so return sticky.
    return START_STICKY;
}

对于app2，这里是建立双向通信绑定(bind)的相关代码:

public final class ComWithIoMcu extends Service {
private static final String TAG = "ComWithIoMcu";
/** Messenger for communicating with service. */
static Messenger mServiceMcu = null;
/** Flag indicating whether we have called bind on the service. */
boolean mIsBound;

/**
 * Command to the service to register a client, receiving callbacks
 * from the service.  The Message's replyTo field must be a Messenger of
 * the client where callbacks should be sent.
 */
static final int MSG_REGISTER_CLIENT = 1;

/**
 * Command to the service to unregister a client, ot stop receiving callbacks
 * from the service.  The Message's replyTo field must be a Messenger of
 * the client as previously given with MSG_REGISTER_CLIENT.
 */
static final int MSG_UNREGISTER_CLIENT = 2;
/**
 * Command to forward a string command to the I/O MCU
 */    
public static final int MSG_SEND_STRING_TO_IOMCU = 3;
/** List of supported commands
 * 
 */
   ...... more code ....

/**
 * Handler of incoming messages from service.
 */
class IncomingHandler extends Handler {
    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
            case MSG_UNSOL_MESSAGE:
                Log.d(TAG, "Received from service: " + msg.arg1);
                break;
            default:
                super.handleMessage(msg);
        }
    }
}

/**
 * Target we publish for clients to send messages to IncomingHandler.
 */
final Messenger mMessenger = new Messenger(new IncomingHandler());
boolean mBound;

/**
 * Class for interacting with the main interface of the service.
 */
private ServiceConnection mConnection = new ServiceConnection() {
    public void onServiceConnected(ComponentName className,
            IBinder service) {
        // This is called when the connection with the service has been
        // established, giving us the service object we can use to
        // interact with the service.  We are communicating with our
        // service through an IDL interface, so get a client-side
        // representation of that from the raw service object.
        mServiceMcu = new Messenger(service);
        Log.d(TAG, "Attached.");

        // We want to monitor the service for as long as we are
        // connected to it.
        try {
            Message msg = Message.obtain(null,
                    MSG_REGISTER_CLIENT);
            msg.replyTo = mMessenger;
            mServiceMcu.send(msg);

        } catch (RemoteException e) {
            // In this case the service has crashed before we could even
            // do anything with it; we can count on soon being
            // disconnected (and then reconnected if it can be restarted)
            // so there is no need to do anything here.
            Log.e(TAG, "ModemWatcherService is not running");
        }
    }

    public void onServiceDisconnected(ComponentName className) {
        // This is called when the connection with the service has been
        // unexpectedly disconnected -- that is, its process crashed.
        mServiceMcu = null;
        mBound = false; 


    }
};

void doBindService() {
    // Establish a connection with the service.  We use an explicit
    // class name because there is no reason to be able to let other
    // applications replace our component.
    //bindService(new Intent(this, MessengerService.class), mConnection, Context.BIND_AUTO_CREATE);
    try {
        Intent intentForMcuService = new Intent();
        Log.d(TAG, "Before init intent.componentName");
        intentForMcuService.setComponent(new ComponentName("com.admetric.modemwatcher", "ModemWatcherService"));
        Log.d(TAG, "Before bindService");
        if (bindService(intentForMcuService, mConnection, 0)){
            Log.d(TAG, "Binding to Modem Watcher returned true");
        } else {
            Log.d(TAG, "Binding to Modem Watcher returned false");
        }
    } catch (SecurityException e) {
        Log.e(TAG, "can't bind to ModemWatcherService, check permission in Manifest");
    }
    mIsBound = true;
    Log.d(TAG, "Binding.");
}

void doUnbindService() {
    if (mIsBound) {
        // If we have received the service, and hence registered with
        // it, then now is the time to unregister.
        if (mServiceMcu != null) {
            try {
                Message msg = Message.obtain(null, MSG_UNREGISTER_CLIENT);
                msg.replyTo = mMessenger;
                mServiceMcu.send(msg);
            } catch (RemoteException e) {
                // There is nothing special we need to do if the service
                // has crashed.
            }
        }

        // Detach our existing connection.
        unbindService(mConnection);
        mIsBound = false;
        Log.d(TAG, "Unbinding.");
    }
}

查看正在运行的服务，我可以看到我在 app2 中创建的服务正在运行。 Logcat 显示我尝试绑定(bind) ModemWatcherService 但未找到。这是 logcat 的有趣部分

12-05 17:22:59.884 D/ComWithIoMcu(  547): Before init intent.componentName
12-05 17:22:59.884 D/ComWithIoMcu(  547): Before bindService
12-05 17:22:59.888 D/ComWithIoMcu(  547): Binding to Modem Watcher returned false
12-05 17:22:59.888 D/ComWithIoMcu(  547): Binding.
12-05 17:22:59.888 W/ActivityManager(   89): Unable to start service Intent { cmp=com.admetric.modemwatcher/ModemWatcherService }: not found

我的第一个想法是我缺少权限，但 bindService() 可以抛出安全异常，在这种情况下并非如此，我检查了一下，它返回 false，原因不明。另外，我知道在 app1 中，永远不会调用 onBind 来证明绑定(bind)从未发生过。所以 logcat 消息“未找到”是有道理的，但我在其 list 中声明该服务是公开的。这可能是一个简单的错误，但我已经关注这个问题一段时间了，但我没有找到原因。知道为什么 app2 在 app1 中找不到服务吗？我只使用剪切和粘贴名称，这样我就不会在名称中犯下愚蠢的错误输入错误。我是否缺少某种权限？我需要做一些额外的步骤来为整个系统发布服务吗？这是我第一次尝试从另一个应用程序访问一个应用程序中的内容，所以我可能错过了一些东西。

Answer 1

您的 ComponentName 构造不正确。传入类名时必须像这样完全限定:

intentForMcuService.setComponent(new ComponentName("com.admetric.modemwatcher",
        "com.admetric.modemwatcher.ModemWatcherService"));

另一件事，如果您在应用程序边界之外引用 Service，最好不要使用 ComponentName 来引用它，即使它确实可以正常工作.一种更常见的方法是为您的 Intent 创建自定义 ACTION 字符串，并让 Service 过滤该操作。