Supporting Controllers Across Android Versions

If you are supporting game controllers in your game, it's your responsibility to make sure that your game responds to controllers consistently across devices running on different versions of Android. This lets your game reach a wider audience, and your players can enjoy a seamless gameplay experience with their controllers even when they switch or upgrade their Android devices.

This lesson demonstrates how to use APIs available in Android 4.1 and higher in a backward compatible way, enabling your game to support the following features on devices running Android 2.3 and higher:

• The game can detect if a new game controller is added, changed, or removed.
• The game can query the capabilities of a game controller.
• The game can recognize incoming motion events from a game controller.

The examples in this lesson are based on the reference implementation provided by the sample ControllerSample.zip available for download above. This sample shows how to implement the InputManagerCompat interface to support different versions of Android. To compile the sample, you must use Android 4.1 (API level 16) or higher. Once compiled, the sample app runs on any device running Android 2.3 (API level 9) or higher as the build target.

Prepare to Abstract APIs for Game Controller Support

Suppose you want to be able to determine if a game controller's connection status has changed on devices running on Android 2.3 (API level 9). However, the APIs are only available in Android 4.1 (API level 16) and higher, so you need to provide an implementation that supports Android 4.1 and higher while providing a fallback mechanism that supports Android 2.3 up to Android 4.0.

To help you determine which features require such a fallback mechanism for older versions, table 1 lists the differences in game controller support between Android 2.3 (API level 9), 3.1 (API level 12), and 4.1 (API level 16).

Table 1. APIs for game controller support across different Android versions.

You can use abstraction to build version-aware game controller support that works across platforms. This approach involves the following steps:

1. Define an intermediary Java interface that abstracts the implementation of the game controller features required by your game.
2. Create a proxy implementation of your interface that uses APIs in Android 4.1 and higher.
3. Create a custom implementation of your interface that uses APIs available between Android 2.3 up to Android 4.0.
4. Create the logic for switching between these implementations at runtime, and begin using the interface in your game.

For an overview of how abstraction can be used to ensure that applications can work in a backward compatible way across different versions of Android, see Creating Backward-Compatible UIs.

Add an Interface for Backward Compatibility

To provide backward compatibility, you can create a custom interface then add version-specific implementations. One advantage of this approach is that it lets you mirror the public interfaces on Android 4.1 (API level 16) that support game controllers.

// The InputManagerCompat interface is a reference example.
// The full code is provided in the ControllerSample.zip sample.
public interface InputManagerCompat {
    ...
    public InputDevice getInputDevice(int id);
    public int[] getInputDeviceIds();

    public void registerInputDeviceListener(
            InputManagerCompat.InputDeviceListener listener,
            Handler handler);
    public void unregisterInputDeviceListener(
            InputManagerCompat.InputDeviceListener listener);

    public void onGenericMotionEvent(MotionEvent event);

    public void onPause();
    public void onResume();

    public interface InputDeviceListener {
        void onInputDeviceAdded(int deviceId);
        void onInputDeviceChanged(int deviceId);
        void onInputDeviceRemoved(int deviceId);
    }
    ...
}

The InputManagerCompat interface provides the following methods:

getInputDevice()

Mirrors getInputDevice(). Obtains the InputDevice object that represents the capabilities of a game controller.

getInputDeviceIds()

Mirrors getInputDeviceIds(). Returns an array of integers, each of which is an ID for a different input device. This is useful if you're building a game that supports multiple players and you want to detect how many controllers are connected.

registerInputDeviceListener()

Mirrors registerInputDeviceListener(). Lets you register to be informed when a new device is added, changed, or removed.

unregisterInputDeviceListener()

Mirrors unregisterInputDeviceListener(). Unregisters an input device listener.

onGenericMotionEvent()

Mirrors onGenericMotionEvent(). Lets your game intercept and handle MotionEvent objects and axis values that represent events such as joystick movements and analog trigger presses.

onPause()

Stops polling for game controller events when the main activity is paused, or when the game no longer has focus.

onResume()

Starts polling for game controller events when the main activity is resumed, or when the game is started and runs in the foreground.

InputDeviceListener

Mirrors the InputManager.InputDeviceListener interface. Lets your game know when a game controller has been added, changed, or removed.

Next, create implementations for InputManagerCompat that work across different platform versions. If your game is running on Android 4.1 or higher and calls an InputManagerCompat method, the proxy implementation calls the equivalent method in InputManager. However, if your game is running on Android 2.3 up to Android 4.0, the custom implementation processes calls to InputManagerCompat methods by using only APIs introduced no later than Android 2.3. Regardless of which version-specific implementation is used at runtime, the implementation passes the call results back transparently to the game.

Figure 1. Class diagram of interface and version-specific implementations.

Implement the Interface on Android 4.1 and Higher

InputManagerCompatV16 is an implementation of the InputManagerCompat interface that proxies method calls to an actual InputManager and InputManager.InputDeviceListener. The InputManager is obtained from the system Context.

// The InputManagerCompatV16 class is a reference implementation.
// The full code is provided in the ControllerSample.zip sample.
public class InputManagerV16 implements InputManagerCompat {

    private final InputManager mInputManager;
    private final Map mListeners;

    public InputManagerV16(Context context) {
        mInputManager = (InputManager)
                context.getSystemService(Context.INPUT_SERVICE);
        mListeners = new HashMap();
    }

    @Override
    public InputDevice getInputDevice(int id) {
        return mInputManager.getInputDevice(id);
    }

    @Override
    public int[] getInputDeviceIds() {
        return mInputManager.getInputDeviceIds();
    }

    static class V16InputDeviceListener implements
            InputManager.InputDeviceListener {
        final InputManagerCompat.InputDeviceListener mIDL;

        public V16InputDeviceListener(InputDeviceListener idl) {
            mIDL = idl;
        }

        @Override
        public void onInputDeviceAdded(int deviceId) {
            mIDL.onInputDeviceAdded(deviceId);
        }

        // Do the same for device change and removal
        ...
    }

    @Override
    public void registerInputDeviceListener(InputDeviceListener listener,
            Handler handler) {
        V16InputDeviceListener v16Listener = new
                V16InputDeviceListener(listener);
        mInputManager.registerInputDeviceListener(v16Listener, handler);
        mListeners.put(listener, v16Listener);
    }

    // Do the same for unregistering an input device listener
    ...

    @Override
    public void onGenericMotionEvent(MotionEvent event) {
        // unused in V16
    }

    @Override
    public void onPause() {
        // unused in V16
    }

    @Override
    public void onResume() {
        // unused in V16
    }

}

Implementing the Interface on Android 2.3 up to Android 4.0

The InputManagerV9 implementation uses APIs introduced no later than Android 2.3. To create an implementation of InputManagerCompat that supports Android 2.3 up to Android 4.0, you can use the following objects:

• A SparseArray of device IDs to track the game controllers that are connected to the device.
• A Handler to process device events. When an app is started or resumed, the Handler receives a message to start polling for game controller disconnection. The Handler will start a loop to check each known connected game controller and see if a device ID is returned. A null return value indicates that the game controller is disconnected. The Handler stops polling when the app is paused.
• A Map of InputManagerCompat.InputDeviceListener objects. You will use the listeners to update the connection status of tracked game controllers.

// The InputManagerCompatV9 class is a reference implementation.
// The full code is provided in the ControllerSample.zip sample.
public class InputManagerV9 implements InputManagerCompat {
    private final SparseArray mDevices;
    private final Map mListeners;
    private final Handler mDefaultHandler;
    …

    public InputManagerV9() {
        mDevices = new SparseArray();
        mListeners = new HashMap();
        mDefaultHandler = new PollingMessageHandler(this);
    }
}

Implement a PollingMessageHandler object that extends Handler, and override the handleMessage() method. This method checks if an attached game controller has been disconnected and notifies registered listeners.

private static class PollingMessageHandler extends Handler {
    private final WeakReference mInputManager;

    PollingMessageHandler(InputManagerV9 im) {
        mInputManager = new WeakReference(im);
    }

    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        switch (msg.what) {
            case MESSAGE_TEST_FOR_DISCONNECT:
                InputManagerV9 imv = mInputManager.get();
                if (null != imv) {
                    long time = SystemClock.elapsedRealtime();
                    int size = imv.mDevices.size();
                    for (int i = 0; i < size; i++) {
                        long[] lastContact = imv.mDevices.valueAt(i);
                        if (null != lastContact) {
                            if (time - lastContact[0] > CHECK_ELAPSED_TIME) {
                                // check to see if the device has been
                                // disconnected
                                int id = imv.mDevices.keyAt(i);
                                if (null == InputDevice.getDevice(id)) {
                                    // Notify the registered listeners
                                    // that the game controller is disconnected
                                    ...
                                    imv.mDevices.remove(id);
                                } else {
                                    lastContact[0] = time;
                                }
                            }
                        }
                    }
                    sendEmptyMessageDelayed(MESSAGE_TEST_FOR_DISCONNECT,
                            CHECK_ELAPSED_TIME);
                }
                break;
        }
    }
}

To start and stop polling for game controller disconnection, override these methods:

private static final int MESSAGE_TEST_FOR_DISCONNECT = 101;
private static final long CHECK_ELAPSED_TIME = 3000L;

@Override
public void onPause() {
    mDefaultHandler.removeMessages(MESSAGE_TEST_FOR_DISCONNECT);
}

@Override
public void onResume() {
    mDefaultHandler.sendEmptyMessageDelayed(MESSAGE_TEST_FOR_DISCONNECT,
            CHECK_ELAPSED_TIME);
}

To detect that an input device has been added, override the onGenericMotionEvent() method. When the system reports a motion event, check if this event came from a device ID that is already tracked, or from a new device ID. If the device ID is new, notify registered listeners.

@Override
public void onGenericMotionEvent(MotionEvent event) {
    // detect new devices
    int id = event.getDeviceId();
    long[] timeArray = mDevices.get(id);
    if (null == timeArray) {
        // Notify the registered listeners that a game controller is added
        ...
        timeArray = new long[1];
        mDevices.put(id, timeArray);
    }
    long time = SystemClock.elapsedRealtime();
    timeArray[0] = time;
}

Notification of listeners is implemented by using the Handler object to send a DeviceEvent Runnable object to the message queue. The DeviceEvent contains a reference to an InputManagerCompat.InputDeviceListener. When the DeviceEvent runs, the appropriate callback method of the listener is called to signal if the game controller was added, changed, or removed.

@Override
public void registerInputDeviceListener(InputDeviceListener listener,
        Handler handler) {
    mListeners.remove(listener);
    if (handler == null) {
        handler = mDefaultHandler;
    }
    mListeners.put(listener, handler);
}

@Override
public void unregisterInputDeviceListener(InputDeviceListener listener) {
    mListeners.remove(listener);
}

private void notifyListeners(int why, int deviceId) {
    // the state of some device has changed
    if (!mListeners.isEmpty()) {
        for (InputDeviceListener listener : mListeners.keySet()) {
            Handler handler = mListeners.get(listener);
            DeviceEvent odc = DeviceEvent.getDeviceEvent(why, deviceId,
                    listener);
            handler.post(odc);
        }
    }
}

private static class DeviceEvent implements Runnable {
    private int mMessageType;
    private int mId;
    private InputDeviceListener mListener;
    private static Queue sObjectQueue =
            new ArrayDeque();
    ...

    static DeviceEvent getDeviceEvent(int messageType, int id,
            InputDeviceListener listener) {
        DeviceEvent curChanged = sObjectQueue.poll();
        if (null == curChanged) {
            curChanged = new DeviceEvent();
        }
        curChanged.mMessageType = messageType;
        curChanged.mId = id;
        curChanged.mListener = listener;
        return curChanged;
    }

    @Override
    public void run() {
        switch (mMessageType) {
            case ON_DEVICE_ADDED:
                mListener.onInputDeviceAdded(mId);
                break;
            case ON_DEVICE_CHANGED:
                mListener.onInputDeviceChanged(mId);
                break;
            case ON_DEVICE_REMOVED:
                mListener.onInputDeviceRemoved(mId);
                break;
            default:
                // Handle unknown message type
                ...
                break;
        }
        // Put this runnable back in the queue
        sObjectQueue.offer(this);
    }
}

You now have two implementations of InputManagerCompat: one that works on devices running Android 4.1 and higher, and another that works on devices running Android 2.3 up to Android 4.0.

Use the Version-Specific Implementation

The version-specific switching logic is implemented in a class that acts as a factory.

public static class Factory {
    public static InputManagerCompat getInputManager(Context context) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
            return new InputManagerV16(context);
        } else {
            return new InputManagerV9();
        }
    }
}

Now you can simply instantiate an InputManagerCompat object and register an InputManagerCompat.InputDeviceListener in your main View. Because of the version-switching logic you set up, your game automatically uses the implementation that's appropriate for the version of Android the device is running.

public class GameView extends View implements InputDeviceListener {
    private InputManagerCompat mInputManager;
    ...

    public GameView(Context context, AttributeSet attrs) {
        mInputManager =
                InputManagerCompat.Factory.getInputManager(this.getContext());
        mInputManager.registerInputDeviceListener(this, null);
        ...
    }
}

Next, override the onGenericMotionEvent() method in your main view, as described in Handle a MotionEvent from a Game Controller. Your game should now be able to process game controller events consistently on devices running Android 2.3 (API level 9) and higher.

@Override
public boolean onGenericMotionEvent(MotionEvent event) {
    mInputManager.onGenericMotionEvent(event);

    // Handle analog input from the controller as normal
    ...
    return super.onGenericMotionEvent(event);
}

You can find a complete implementation of this compatibility code in the GameView class provided in the sample ControllerSample.zip available for download above.