Wi-Fi Direct（也称为点对点或 P2P）允许您的应用程序快速查找并与附近的设备交互，其范围超出蓝牙的功能。
Wi-Fi Direct (P2P) API 允许应用程序连接到附近的设备，而无需连接到网络或热点。如果您的应用旨在成为安全近距离网络的一部分，则 Wi-Fi Direct 比传统的 Wi-Fi 自组网络更合适，原因如下：
- Wi-Fi Direct 支持 WPA2 加密。（某些自组网络仅支持 WEP 加密。）
- 设备可以广播它们提供的服务，这有助于其他设备更轻松地发现合适的对等节点。
- 在确定哪个设备应成为网络的组所有者时，Wi-Fi Direct 会检查每个设备的电源管理、UI 和服务功能，并使用这些信息来选择能够最有效地处理服务器职责的设备。
- Android 不支持 Wi-Fi 自组模式。
本课程将向您展示如何使用 Wi-Fi P2P 查找并连接到附近的设备。
设置应用程序权限
要使用 Wi-Fi Direct，请将ACCESS_FINE_LOCATION、CHANGE_WIFI_STATE、ACCESS_WIFI_STATE和INTERNET权限添加到您的清单中。如果您的应用面向 Android 13（API 级别 33）或更高版本，则还应将NEARBY_WIFI_DEVICES权限添加到您的清单中。Wi-Fi Direct 不需要互联网连接，但它确实使用标准的 Java 套接字，这需要INTERNET权限。因此，您需要以下权限才能使用 Wi-Fi Direct：
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.nsdchat"
...
<!-- If your app targets Android 13 (API level 33)
or higher, you must declare the NEARBY_WIFI_DEVICES permission. -->
<uses-permission android:name="android.permission.NEARBY_WIFI_DEVICES"
<!-- If your app derives location information from Wi-Fi APIs,
don't include the "usesPermissionFlags" attribute. -->
android:usesPermissionFlags="neverForLocation" />
<uses-permission
android:required="true"
android:name="android.permission.ACCESS_FINE_LOCATION"
<!-- If any feature in your app relies on precise location information,
don't include the "maxSdkVersion" attribute. -->
android:maxSdkVersion="32" />
<uses-permission
android:required="true"
android:name="android.permission.ACCESS_WIFI_STATE"/>
<uses-permission
android:required="true"
android:name="android.permission.CHANGE_WIFI_STATE"/>
<uses-permission
android:required="true"
android:name="android.permission.INTERNET"/>
...
除了上述权限外，以下 API 还需要启用位置模式：
设置广播接收器和点对点管理器
要使用 Wi-Fi Direct，您需要侦听广播意图，这些意图会告知您的应用程序何时发生某些事件。在您的应用程序中，实例化一个IntentFilter并将其设置为侦听以下内容：
WIFI_P2P_STATE_CHANGED_ACTION- 指示 Wi-Fi Direct 是否已启用。
WIFI_P2P_PEERS_CHANGED_ACTION- 指示可用的对等节点列表已更改。
WIFI_P2P_CONNECTION_CHANGED_ACTION- 指示 Wi-Fi Direct 连接状态已更改。从 Android 10 开始，此广播不再是粘性的。如果您的应用一直依赖于在注册时接收这些广播，因为它们一直是粘性的，请改用初始化时的相应
get方法来获取信息。 WIFI_P2P_THIS_DEVICE_CHANGED_ACTION- 指示此设备的配置详细信息已更改。从 Android 10 开始，此广播不再是粘性的。如果您的应用在注册时依赖于接收这些广播（因为它们一直是粘性的），请改用初始化时的适当
get方法获取信息。
Kotlin
private val intentFilter = IntentFilter()
...
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.main)
// Indicates a change in the Wi-Fi Direct status.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION)
// Indicates a change in the list of available peers.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION)
// Indicates the state of Wi-Fi Direct connectivity has changed.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION)
// Indicates this device's details have changed.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION)
...
}
Java
private final IntentFilter intentFilter = new IntentFilter();
...
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Indicates a change in the Wi-Fi Direct status.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);
// Indicates a change in the list of available peers.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);
// Indicates the state of Wi-Fi Direct connectivity has changed.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);
// Indicates this device's details have changed.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);
...
}
在 onCreate() 方法的末尾，获取 WifiP2pManager 的实例，并调用其 initialize() 方法。此方法返回一个 WifiP2pManager.Channel 对象，您稍后将使用它来连接您的应用到 Wi-Fi Direct 框架。
Kotlin
private lateinit var channel: WifiP2pManager.Channel
private lateinit var manager: WifiP2pManager
override fun onCreate(savedInstanceState: Bundle?) {
...
manager = getSystemService(Context.WIFI_P2P_SERVICE) as WifiP2pManager
channel = manager.initialize(this, mainLooper, null)
}
Java
Channel channel;
WifiP2pManager manager;
@Override
public void onCreate(Bundle savedInstanceState) {
...
manager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);
channel = manager.initialize(this, getMainLooper(), null);
}
现在创建一个新的 BroadcastReceiver 类，用于监听系统 Wi-Fi 状态的变化。在 onReceive() 方法中，添加一个条件来处理上面列出的每种状态更改。
Kotlin
override fun onReceive(context: Context, intent: Intent) {
when(intent.action) {
WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION -> {
// Determine if Wi-Fi Direct mode is enabled or not, alert
// the Activity.
val state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1)
activity.isWifiP2pEnabled = state == WifiP2pManager.WIFI_P2P_STATE_ENABLED
}
WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION -> {
// The peer list has changed! We should probably do something about
// that.
}
WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION -> {
// Connection state changed! We should probably do something about
// that.
}
WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION -> {
(activity.supportFragmentManager.findFragmentById(R.id.frag_list) as DeviceListFragment)
.apply {
updateThisDevice(
intent.getParcelableExtra(
WifiP2pManager.EXTRA_WIFI_P2P_DEVICE) as WifiP2pDevice
)
}
}
}
}
Java
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) {
// Determine if Wi-Fi Direct mode is enabled or not, alert
// the Activity.
int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1);
if (state == WifiP2pManager.WIFI_P2P_STATE_ENABLED) {
activity.setIsWifiP2pEnabled(true);
} else {
activity.setIsWifiP2pEnabled(false);
}
} else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {
// The peer list has changed! We should probably do something about
// that.
} else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {
// Connection state changed! We should probably do something about
// that.
} else if (WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)) {
DeviceListFragment fragment = (DeviceListFragment) activity.getFragmentManager()
.findFragmentById(R.id.frag_list);
fragment.updateThisDevice((WifiP2pDevice) intent.getParcelableExtra(
WifiP2pManager.EXTRA_WIFI_P2P_DEVICE));
}
}
最后，添加代码以在主活动处于活动状态时注册意图过滤器和广播接收器，并在活动暂停时取消注册它们。执行此操作的最佳位置是 onResume() 和 onPause() 方法。
Kotlin
/** register the BroadcastReceiver with the intent values to be matched */
public override fun onResume() {
super.onResume()
receiver = WiFiDirectBroadcastReceiver(manager, channel, this)
registerReceiver(receiver, intentFilter)
}
public override fun onPause() {
super.onPause()
unregisterReceiver(receiver)
}
Java
/** register the BroadcastReceiver with the intent values to be matched */
@Override
public void onResume() {
super.onResume();
receiver = new WiFiDirectBroadcastReceiver(manager, channel, this);
registerReceiver(receiver, intentFilter);
}
@Override
public void onPause() {
super.onPause();
unregisterReceiver(receiver);
}
启动对等发现
要开始搜索附近具有 Wi-Fi P2P 功能的设备，请调用 discoverPeers()。此方法采用以下参数
- 您在初始化对等管理器时收到的
WifiP2pManager.Channel WifiP2pManager.ActionListener的实现，其中包含系统为成功和不成功发现调用的方法。
Kotlin
manager.discoverPeers(channel, object : WifiP2pManager.ActionListener {
override fun onSuccess() {
// Code for when the discovery initiation is successful goes here.
// No services have actually been discovered yet, so this method
// can often be left blank. Code for peer discovery goes in the
// onReceive method, detailed below.
}
override fun onFailure(reasonCode: Int) {
// Code for when the discovery initiation fails goes here.
// Alert the user that something went wrong.
}
})
Java
manager.discoverPeers(channel, new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
// Code for when the discovery initiation is successful goes here.
// No services have actually been discovered yet, so this method
// can often be left blank. Code for peer discovery goes in the
// onReceive method, detailed below.
}
@Override
public void onFailure(int reasonCode) {
// Code for when the discovery initiation fails goes here.
// Alert the user that something went wrong.
}
});
请记住，这仅 *启动* 对等发现。 discoverPeers() 方法启动发现过程，然后立即返回。系统会通过调用提供的操作侦听器中的方法来通知您是否已成功启动对等发现过程。此外，发现将保持活动状态，直到启动连接或形成 P2P 组。
获取对等设备列表
现在编写获取和处理对等设备列表的代码。首先实现 WifiP2pManager.PeerListListener 接口，该接口提供有关 Wi-Fi Direct 检测到的对等设备的信息。此信息还允许您的应用确定对等设备何时加入或离开网络。以下代码片段说明了与对等设备相关的这些操作
Kotlin
private val peers = mutableListOf<WifiP2pDevice>()
...
private val peerListListener = WifiP2pManager.PeerListListener { peerList ->
val refreshedPeers = peerList.deviceList
if (refreshedPeers != peers) {
peers.clear()
peers.addAll(refreshedPeers)
// If an AdapterView is backed by this data, notify it
// of the change. For instance, if you have a ListView of
// available peers, trigger an update.
(listAdapter as WiFiPeerListAdapter).notifyDataSetChanged()
// Perform any other updates needed based on the new list of
// peers connected to the Wi-Fi P2P network.
}
if (peers.isEmpty()) {
Log.d(TAG, "No devices found")
return@PeerListListener
}
}
Java
private List<WifiP2pDevice> peers = new ArrayList<WifiP2pDevice>();
...
private PeerListListener peerListListener = new PeerListListener() {
@Override
public void onPeersAvailable(WifiP2pDeviceList peerList) {
List<WifiP2pDevice> refreshedPeers = peerList.getDeviceList();
if (!refreshedPeers.equals(peers)) {
peers.clear();
peers.addAll(refreshedPeers);
// If an AdapterView is backed by this data, notify it
// of the change. For instance, if you have a ListView of
// available peers, trigger an update.
((WiFiPeerListAdapter) getListAdapter()).notifyDataSetChanged();
// Perform any other updates needed based on the new list of
// peers connected to the Wi-Fi P2P network.
}
if (peers.size() == 0) {
Log.d(WiFiDirectActivity.TAG, "No devices found");
return;
}
}
}
现在修改广播接收器的 onReceive() 方法，以便在接收到操作为 WIFI_P2P_PEERS_CHANGED_ACTION 的意图时调用 requestPeers()。您需要以某种方式将此侦听器传递给接收器。一种方法是将其作为参数发送到广播接收器的构造函数。
Kotlin
fun onReceive(context: Context, intent: Intent) {
when (intent.action) {
...
WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION -> {
// Request available peers from the wifi p2p manager. This is an
// asynchronous call and the calling activity is notified with a
// callback on PeerListListener.onPeersAvailable()
mManager?.requestPeers(channel, peerListListener)
Log.d(TAG, "P2P peers changed")
}
...
}
}
Java
public void onReceive(Context context, Intent intent) {
...
else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {
// Request available peers from the wifi p2p manager. This is an
// asynchronous call and the calling activity is notified with a
// callback on PeerListListener.onPeersAvailable()
if (mManager != null) {
mManager.requestPeers(channel, peerListListener);
}
Log.d(WiFiDirectActivity.TAG, "P2P peers changed");
}...
}
现在，操作为 WIFI_P2P_PEERS_CHANGED_ACTION 的意图会触发对更新的对等设备列表的请求。
连接到对等设备
为了连接到对等设备，创建一个新的 WifiP2pConfig 对象，并将数据从表示您要连接到的设备的 WifiP2pDevice 复制到其中。然后调用 connect() 方法。
Kotlin
override fun connect() {
// Picking the first device found on the network.
val device = peers[0]
val config = WifiP2pConfig().apply {
deviceAddress = device.deviceAddress
wps.setup = WpsInfo.PBC
}
manager.connect(channel, config, object : WifiP2pManager.ActionListener {
override fun onSuccess() {
// WiFiDirectBroadcastReceiver notifies us. Ignore for now.
}
override fun onFailure(reason: Int) {
Toast.makeText(
this@WiFiDirectActivity,
"Connect failed. Retry.",
Toast.LENGTH_SHORT
).show()
}
})
}
Java
@Override
public void connect() {
// Picking the first device found on the network.
WifiP2pDevice device = peers.get(0);
WifiP2pConfig config = new WifiP2pConfig();
config.deviceAddress = device.deviceAddress;
config.wps.setup = WpsInfo.PBC;
manager.connect(channel, config, new ActionListener() {
@Override
public void onSuccess() {
// WiFiDirectBroadcastReceiver notifies us. Ignore for now.
}
@Override
public void onFailure(int reason) {
Toast.makeText(WiFiDirectActivity.this, "Connect failed. Retry.",
Toast.LENGTH_SHORT).show();
}
});
}
如果组中的每个设备都支持 Wi-Fi Direct，则在连接时无需显式请求组的密码。但是，要允许不支持 Wi-Fi Direct 的设备加入组，您需要通过调用 requestGroupInfo() 来检索此密码，如下面的代码片段所示
Kotlin
manager.requestGroupInfo(channel) { group ->
val groupPassword = group.passphrase
}
Java
manager.requestGroupInfo(channel, new GroupInfoListener() {
@Override
public void onGroupInfoAvailable(WifiP2pGroup group) {
String groupPassword = group.getPassphrase();
}
});
请注意，在 connect() 方法中实现的 WifiP2pManager.ActionListener 仅在 *初始化* 成功或失败时通知您。要侦听连接状态的 *更改*，请实现 WifiP2pManager.ConnectionInfoListener 接口。其 onConnectionInfoAvailable() 回调会在连接状态发生变化时通知您。在多个设备将连接到单个设备（例如，具有三个或更多玩家的游戏或聊天应用）的情况下，一个设备被指定为“组所有者”。您可以按照 创建组 部分中的步骤，将特定设备指定为网络的组所有者。
Kotlin
private val connectionListener = WifiP2pManager.ConnectionInfoListener { info ->
// String from WifiP2pInfo struct
val groupOwnerAddress: String = info.groupOwnerAddress.hostAddress
// After the group negotiation, we can determine the group owner
// (server).
if (info.groupFormed && info.isGroupOwner) {
// Do whatever tasks are specific to the group owner.
// One common case is creating a group owner thread and accepting
// incoming connections.
} else if (info.groupFormed) {
// The other device acts as the peer (client). In this case,
// you'll want to create a peer thread that connects
// to the group owner.
}
}
Java
@Override
public void onConnectionInfoAvailable(final WifiP2pInfo info) {
// String from WifiP2pInfo struct
String groupOwnerAddress = info.groupOwnerAddress.getHostAddress();
// After the group negotiation, we can determine the group owner
// (server).
if (info.groupFormed && info.isGroupOwner) {
// Do whatever tasks are specific to the group owner.
// One common case is creating a group owner thread and accepting
// incoming connections.
} else if (info.groupFormed) {
// The other device acts as the peer (client). In this case,
// you'll want to create a peer thread that connects
// to the group owner.
}
}
现在返回到广播接收器的 onReceive() 方法，并修改侦听 WIFI_P2P_CONNECTION_CHANGED_ACTION 意图的部分。当接收到此意图时，调用 requestConnectionInfo()。这是一个异步调用，因此结果由您作为参数提供的连接信息侦听器接收。
Kotlin
when (intent.action) {
...
WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION -> {
// Connection state changed! We should probably do something about
// that.
mManager?.let { manager ->
val networkInfo: NetworkInfo? = intent
.getParcelableExtra(WifiP2pManager.EXTRA_NETWORK_INFO) as NetworkInfo
if (networkInfo?.isConnected == true) {
// We are connected with the other device, request connection
// info to find group owner IP
manager.requestConnectionInfo(channel, connectionListener)
}
}
}
...
}
Java
...
} else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {
if (manager == null) {
return;
}
NetworkInfo networkInfo = (NetworkInfo) intent
.getParcelableExtra(WifiP2pManager.EXTRA_NETWORK_INFO);
if (networkInfo.isConnected()) {
// We are connected with the other device, request connection
// info to find group owner IP
manager.requestConnectionInfo(channel, connectionListener);
}
...
创建组
如果您希望运行您的应用的设备充当包含旧版设备（即不支持 Wi-Fi Direct 的设备）的网络的组所有者，则按照与 连接到对等设备 部分相同的步骤顺序进行操作，除了使用 createGroup() 而不是 connect() 创建新的 WifiP2pManager.ActionListener。 WifiP2pManager.ActionListener 内的回调处理相同，如下面的代码片段所示
Kotlin
manager.createGroup(channel, object : WifiP2pManager.ActionListener {
override fun onSuccess() {
// Device is ready to accept incoming connections from peers.
}
override fun onFailure(reason: Int) {
Toast.makeText(
this@WiFiDirectActivity,
"P2P group creation failed. Retry.",
Toast.LENGTH_SHORT
).show()
}
})
Java
manager.createGroup(channel, new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
// Device is ready to accept incoming connections from peers.
}
@Override
public void onFailure(int reason) {
Toast.makeText(WiFiDirectActivity.this, "P2P group creation failed. Retry.",
Toast.LENGTH_SHORT).show();
}
});
注意：如果网络中的所有设备都支持 Wi-Fi Direct，则可以在每个设备上使用 connect() 方法，因为该方法会创建组并自动选择组所有者。
创建组后，您可以调用 requestGroupInfo() 以检索有关网络上对等设备的详细信息，包括设备名称和连接状态。