Question

I’m trying to start a service on android in order to performe some network-related tasks in background. I have written a basic network-manager for my app, which is a service. I basically used the tutorial from the android documentation. The basic structure goes as following:

public class MyNetworkManager extends Service {
// some code

private final IBinder mBinder = (IBinder) new MyBinder();
@Override
public IBinder onBind(Intent arg0) {
  return mBinder;
}

public class MyBinder extends Binder {
   MyNetworkManager getService() {
        return MyNetworkManager.this;
    }
}

public void onCreate() {
// some network related stuff like setting up sockets etc.
}

public void onStart(Intent intent, int startid) {
    while(true) {
        // receive new connections etc
    }
}

The calling app/activity is then:

public class AndroidNetworkManagerClient extends Activity {
  private Button buttonSend;
  private EditText inputText;
  private TextView outputText;
  private MyNetworkManager networkManager;

  private ServiceConnection mConnection = new ServiceConnection() {

        public void onServiceConnected(ComponentName className, IBinder binder) {
            networkManager = ((MyNetworkManager.MyBinder) binder).getService();
        }

        public void onServiceDisconnected(ComponentName className) {
            networkManager = null;
        }
    };

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

      inputText = (EditText) findViewById(R.id.textInput);
      outputText = (TextView) findViewById(R.id.textOutput);
      buttonSend = (Button)this.findViewById(R.id.buttonSend);
      buttonSend.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            if (inputText.getText().length() != 0) {
                outputText.append("Out: " + inputText.getText() + "\n");
                networkManager.sendData("localhost", inputText.getText().toString());
            }
        }
    });


      bindService(new Intent(this, MyNetworkManager.class), mConnection, Context.BIND_AUTO_CREATE);

      doSomeAppRelatedStuff();
  }

bindService() seems to be called without any problems, but the variable “networkManager” is always null! I already tried to debug into the onCreate() method or onServiceConnected() but it seems, that these parts are not reached at all (at least no breakpoint was triggered).

The service is already registered in the AndroidManifest.xml:

package="some.random.name"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk android:minSdkVersion="8" /> 
<uses-permission android:name="android.permission.INTERNET"></uses-permission> 

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name" >
    <activity
        android:name=".AndroidNetworkManagerClient"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <service android:name=".MyNetworkManager"></service>
</application>

Anyone an idea?

Answer 1

Chances are, your Activity is getting into doSomeAppRelatedStuff() and trying to use networkManager before the binding is complete.

If doSomeAppRelatedStuff() absolutely must have the network manager to function, move your call to doSomeAppRelatedStuff() into onServiceConnected() so it won’t actually start until the binding is complete. Note that if you do that, your onStart() and onResume() calls will probably (but not guaranteed!) happen before the binding is complete, so program accordingly.