1page.title=Supporting Multiple Game Controllers
2trainingnavtop=true
3
4@jd:body
5
6<!-- This is the training bar -->
7<div id="tb-wrapper">
8<div id="tb">
9
10<h2>This lesson teaches you to</h2>
11<ol>
12  <li><a href="#map">Map Players to Controller Device IDs</a></li>
13  <li><a href="#detect">Process Multiple Controller Input</a></li>
14</ol>
15
16<h2>Try it out</h2>
17<div class="download-box">
18  <a href="http://developer.android.com/shareables/training/ControllerSample.zip"
19class="button">Download the sample</a>
20  <p class="filename">ControllerSample.zip</p>
21</div>
22
23
24</div>
25</div>
26<p>While most games are designed to support a single user per Android device,
27it's also possible to support multiple users with game controllers that are
28connected simultaneously on the same Android device.</p>
29<p>This lesson covers some basic techniques for handling input in your single
30device multiplayer game from multiple connected controllers. This includes
31maintaining a mapping between player avatars and each controller device and
32processing controller input events appropriately.
33</p>
34
35<h2 id="map">Map Players to Controller Device IDs</h2>
36<p>When a game controller is connected to an Android device, the system
37assigns it an integer device ID. You can obtain the device IDs for connected
38game controllers by calling {@link android.view.InputDevice#getDeviceIds() InputDevice.getDeviceIds()}, as shown in <a href="controller-input.html#input">Verify a Game Controller is Connected</a>. You can then associate each
39device ID with a player in your game, and process game actions for each player separately.
40</p>
41<p class="note"><strong>Note: </strong>On devices running Android 4.1 (API
42level 16) and higher, you can obtain an input device’s descriptor using
43{@link android.view.InputDevice#getDescriptor()}, which returns a unique
44persistent string value for the input device. Unlike a device ID, the descriptor
45value won't change even if the input device is disconnected, reconnected, or
46reconfigured.
47</p>
48<p>The code snippet below shows how to use a {@link android.util.SparseArray}
49to associate a player's avatar with a specific controller. In this example, the
50{@code mShips} variable stores a collection of {@code Ship} objects. A new
51player avatar is created in-game when a new controller is attached by a user,
52and removed when its associated controller is removed.
53</p>
54<p>The {@code onInputDeviceAdded()} and {@code onInputDeviceRemoved()} callback
55methods are part of the abstraction layer introduced in
56<a href="{@docRoot}training/game-controllers/compatibility.html#status_callbacks}">
57Supporting Controllers Across Android Versions</a>. By implementing these
58listener callbacks, your game can identify the game controller's device ID when a
59controller is added or removed. This detection is compatible with Android 2.3
60(API level 9) and higher.
61</p>
62
63<pre>
64private final SparseArray&lt;Ship&gt; mShips = new SparseArray&lt;Ship&gt;();
65
66&#64;Override
67public void onInputDeviceAdded(int deviceId) {
68    getShipForID(deviceId);
69}
70
71&#64;Override
72public void onInputDeviceRemoved(int deviceId) {
73    removeShipForID(deviceId);
74}
75
76private Ship getShipForID(int shipID) {
77    Ship currentShip = mShips.get(shipID);
78    if ( null == currentShip ) {
79        currentShip = new Ship();
80        mShips.append(shipID, currentShip);
81    }
82    return currentShip;
83}
84
85private void removeShipForID(int shipID) {
86    mShips.remove(shipID);
87}
88</pre>
89
90<h2 id="detect">Process Multiple Controller Input</h2>
91<p>Your game should execute the following loop to process
92input from multiple controllers:
93</p>
94<ol>
95<li>Detect whether an input event occurred.</li>
96<li>Identify the input source and its device ID.</li>
97<li>Based on the action indicated by the input event key code or axis value,
98    update the player avatar associated with that device ID.</li>
99<li>Render and update the user interface.</li>
100</ol>
101<p>{@link android.view.KeyEvent} and {@link android.view.MotionEvent} input
102events have device IDs associated with them. Your game can take advantage of
103this to determine which controller the input event came from, and update the
104player avatar associated with that controller.
105</p>
106<p>The following code snippet shows how you might get a player avatar reference
107corresponding to a game controller device ID, and update the game based on the
108user's button press on that controller.
109</p>
110<pre>
111&#64;Override
112public boolean onKeyDown(int keyCode, KeyEvent event) {
113    if ((event.getSource() &amp; InputDevice.SOURCE_GAMEPAD)
114                == InputDevice.SOURCE_GAMEPAD) {
115        int deviceId = event.getDeviceId();
116        if (deviceId != -1) {
117            Ship currentShip = getShipForId(deviceId);
118            // Based on which key was pressed, update the player avatar
119            // (e.g. set the ship headings or fire lasers)
120            ...
121            return true;
122        }
123    }
124    return super.onKeyDown(keyCode, event);
125}
126</pre>
127<p class="note"><strong>Note: </strong>As a best practice, when a user's
128game controller disconnects, you should pause the game and ask if the user
129wants to reconnect.
130</p>
131