onServiceConnected never called after bindService

问题:

I have a particular situation: a service started by a broadcast receiver starts an activity. I want to make it possible for this activity to communicate back to the service. I have chosen to use AIDL to make it possible. Everything seems works good except for bindService() method called in onCreate() of the activity. bindService(), in fact, throws a null pointer exception because onServiceConnected() is never called while onBind() method of the service is. Anyway bindService() returns true. The service is obviously active because it starts the activity. I know that calling an activity from a service could sound strange, but unfortunately this is the only way to have speech recognition in a service.

Thanks in advance

回答1:

I can't make up the exact problem out of your description, so I'm going to guess here!

How can bindService() throw a NullPointerException? The only way this could (/should) happen is when you don't supply a Service or a ServiceConnection listener.

bindService() can't throw a NullPointerException because onServiceConnected() isn't called. The call to onServiceConnected() is a product of bindService().

So I guess you are calling a AIDL method, before the Service has actually bonded?

回答2:

I've just experienced another version of this problem, with the same symptom of onServiceConnected(...) not being called. The cause was different in my case.

You must make sure to have a service declaration in your AndroidManifest.xml within the application tag - this was the root of the problem for me.

<application android:name=".YourAppTitle" android:icon="@drawable/icon" android:label="@string/app_name">
    <activity android:name=".Main" android:label="@string/app_name">
    </activity>
    <service android:name="YourService" />
</application>

There's an extra complication if you're using a separate Android library within Eclipse - adding this Service tag only seems to fix the issue if the referenced service is in the same package as the manifest; i.e. if your app is in package a.b.c and this is where AndroidManifest.xml resides, then 'YourService' must also be in package a.b.c. (manually copied from another library, if necessary) or else the <service..> tag may/will be ignored and onServiceConnected(...) still won't be called.

This was the case for my project even though I used a suitable import statement for the Service in my code. Eclipse showed no error, so the import was correctly identifying the class from another library in the Eclipse workspace.

HTH

回答3:

After hours and hours of trying to figure this out, the issue is that the examples that show the creation of the service, don't include the onBind method or they have the following sample code or it generates this for you:

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

This causes the onServiceConnected method to fail or never actually get executed. The fix is VERY simple, which is the following:

public IBinder onBind(Intent intent) {
    return mBinder;
}

Where you could create a simple binder such as the following to return:

private final IBinder mBinder = new LocalBinder();
public class LocalBinder extends Binder {
    public ConferenceService getService() {
    return ConferenceService.this;
  }
}

回答4:

The onServiceConnected event was never being called in my application.

The problem was that I had the service name defined in my Application Manifest as:

<service android:name="MyService" android:enabled="true"></service>

Once I changed it to the full class name it worked:

<service android:name="com.example.MyService" android:enabled="true"></service>

Update: You can also have use a relative class name:

<service android:name=".MyService" android:enabled="true"></service>

Specify the class name using its full com.example.MyServiceClass instead of just MyServiceClass.

回答5:

One more thing is that if you are calling bindservice method inside the oncreate method then the onserviceconnected is called after the oncreate method is finished.

So any references to the interface functions before the oncreate ends (or before onserviceconnected is called) shows null pointer exception.

回答6:

Yet another cause to the original question might be that the service isn't already running and you are passing 0 as flag to bindService. Like so:

bindService(intent, serviceConnection, 0);

When what you are looking for would be:

bindService(intent, serviceConnection, Context.BIND_AUTO_CREATE);

回答7:

There can be another explanation, not a very frequent situation, but I managed to get into it and lose 2 hours to solve it.

So what I did was that I wanted to reuse the bundle from the intent received by the onBind method. But I went for the lazy version and changed the class of the intent. Apparently this causes the onServiceConnected not to get called. Probably because the system keeps a reference to the intent and uses it when calling onServiceConnected.

In conclusion don't change the intent you receive in onBind.

回答8:

I was calling bind with an empty Intent - getContext().bindService(new Intent(), mConnection, Context.BIND_AUTO_CREATE). I have to make the intent more specific to indicate which service I want to bind to. This is obviously a code error, but the Logcat output was unfortunately not clear enough.