While most games are designed to support a single user per Android device, it's also possible to support multiple users with game controllers that are connected simultaneously on the same Android device.

This lesson covers some basic techniques for handling input in your single device multiplayer game from multiple connected controllers. This includes maintaining a mapping between player avatars and each controller device and processing controller input events appropriately.

## Map players to controller device IDs

When a game controller is connected to an Android device, the system assigns it an integer device ID. You can obtain the device IDs for connected game controllers by calling[InputDevice.getDeviceIds()](https://developer.android.com/reference/android/view/InputDevice#getDeviceIds()), as shown in[Verify a Game Controller is Connected](https://developer.android.com/develop/ui/views/touch-and-input/game-controllers/controller-input#input). You can then associate each device ID with a player in your game, and process game actions for each player separately.

**Note:** On devices running Android 4.1 (API level 16) and higher, you can obtain an input device's descriptor using[getDescriptor()](https://developer.android.com/reference/android/view/InputDevice#getDescriptor()), which returns a unique persistent string value for the input device. Unlike a device ID, the descriptor value won't change even if the input device is disconnected, reconnected, or reconfigured.

The code snippet below shows how to use a[SparseArray](https://developer.android.com/reference/android/util/SparseArray)to associate a player's avatar with a specific controller. In this example, the`mShips`variable stores a collection of`Ship`objects. A new player avatar is created in-game when a new controller is attached by a user, and removed when its associated controller is removed.

The`onInputDeviceAdded()`and`onInputDeviceRemoved()`callback methods are part of the abstraction layer introduced in[Supporting Controllers Across Android Versions](https://developer.android.com/training/game-controllers/compatibility#status_callbacks}). By implementing these listener callbacks, your game can identify the game controller's device ID when a controller is added or removed. This detection is compatible with Android 2.3 (API level 9) and higher.  

### Kotlin

```kotlin
private val ships = SparseArray<Ship>()

override fun onInputDeviceAdded(deviceId: Int) {
    getShipForID(deviceId)
}

override fun onInputDeviceRemoved(deviceId: Int) {
    removeShipForID(deviceId)
}

private fun getShipForID(shipID: Int): Ship {
    return ships.get(shipID) ?: Ship().also {
        ships.append(shipID, it)
    }
}

private fun removeShipForID(shipID: Int) {
    ships.remove(shipID)
}
```

### Java

```java
private final SparseArray<Ship> ships = new SparseArray<Ship>();

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

@Override
public void onInputDeviceRemoved(int deviceId) {
    removeShipForID(deviceId);
}

private Ship getShipForID(int shipID) {
    Ship currentShip = ships.get(shipID);
    if ( null == currentShip ) {
        currentShip = new Ship();
        ships.append(shipID, currentShip);
    }
    return currentShip;
}

private void removeShipForID(int shipID) {
    ships.remove(shipID);
}
```

## Process multiple controller input

Your game should execute the following loop to process input from multiple controllers:

1. Detect whether an input event occurred.
2. Identify the input source and its device ID.
3. Based on the action indicated by the input event key code or axis value, update the player avatar associated with that device ID.
4. Render and update the user interface.

[KeyEvent](https://developer.android.com/reference/android/view/KeyEvent)and[MotionEvent](https://developer.android.com/reference/android/view/MotionEvent)input events have device IDs associated with them. Your game can take advantage of this to determine which controller the input event came from, and update the player avatar associated with that controller.

The following code snippet shows how you might get a player avatar reference corresponding to a game controller device ID, and update the game based on the user's button press on that controller.  

### Kotlin

```kotlin
override fun onKeyDown(keyCode: Int, event: KeyEvent): Boolean {
    if (event.source and InputDevice.SOURCE_GAMEPAD == InputDevice.SOURCE_GAMEPAD) {
        event.deviceId.takeIf { it != -1 }?.also { deviceId ->
            val currentShip: Ship = getShipForID(deviceId)
            // Based on which key was pressed, update the player avatar
            // (e.g. set the ship headings or fire lasers)
            return true
        }
    }
    return super.onKeyDown(keyCode, event)
}
```

### Java

```java
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if ((event.getSource() & InputDevice.SOURCE_GAMEPAD)
                == InputDevice.SOURCE_GAMEPAD) {
        int deviceId = event.getDeviceId();
        if (deviceId != -1) {
            Ship currentShip = getShipForId(deviceId);
            // Based on which key was pressed, update the player avatar
            // (e.g. set the ship headings or fire lasers)
            ...
            return true;
        }
    }
    return super.onKeyDown(keyCode, event);
}
```

**Note:**As a best practice, when a user's game controller disconnects, you should pause the game and ask if the user wants to reconnect.