Wi-Fi Direct (也稱為點對點或 P2P) 可讓應用程式在藍牙功能範圍以外的距離，快速尋找並與附近裝置互動。
Wi-Fi Direct (P2P) API 可讓應用程式連線至附近裝置，而不需要連線至網路或無線基地台。如果您的應用程式是用於安全的近距離網路，Wi-Fi Direct 比傳統 Wi-Fi 臨時網路更適合，原因如下：
- Wi-Fi Direct 支援 WPA2 加密。(部分臨機操作網路僅支援 WEP 加密)。
- 裝置可以廣播其提供的服務，方便其他裝置輕鬆找到適合的裝置。
- 在決定哪部裝置應成為網路的群組擁有者時，Wi-Fi Direct 會檢查每部裝置的電源管理、使用者介面和服務功能，並利用這些資訊選擇最能有效處理伺服器責任的裝置。
- Android 不支援 Wi-Fi 臨機操作模式。
本課程將說明如何使用 Wi-Fi P2P 尋找並連線至附近的裝置。
設定應用程式權限
如要使用 Wi-Fi Direct，請在資訊清單中新增 ACCESS_FINE_LOCATION、CHANGE_WIFI_STATE、ACCESS_WIFI_STATE 和 INTERNET 權限。如果應用程式指定 Android 13 (API 級別 33) 以上版本，請一併在資訊清單中新增 NEARBY_WIFI_DEVICES 權限。Wi-Fi Direct 不需要網際網路連線，但會使用標準 Java 套接字，而這需要 INTERNET 權限。因此，您需要具備下列權限才能使用 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"/>
...
除了上述權限之外，下列 API 也需要啟用位置模式：
設定廣播接收器和對等端管理工具
如要使用 Wi-Fi Direct，您必須監聽廣播意圖，以便在特定事件發生時通知應用程式。在應用程式中，將 IntentFilter 例項化，並將其設為聆聽下列項目：
WIFI_P2P_STATE_CHANGED_ACTION- 指出是否已啟用 Wi-Fi Direct
WIFI_P2P_PEERS_CHANGED_ACTION- 表示可用的同類組合清單已變更。
WIFI_P2P_CONNECTION_CHANGED_ACTION-
表示 Wi-Fi Direct 連線狀態已變更。自 Android 10 起，這項設定不再固定。如果您的應用程式會在註冊時接收這些廣播訊息，因為這些廣播訊息會持續存在，請改為在初始化時使用適當的
get方法來取得資訊。 WIFI_P2P_THIS_DEVICE_CHANGED_ACTION-
表示此裝置的設定詳細資料已變更。自 Android 10 起，這項設定不再固定。如果您的應用程式會在註冊時接收這些廣播訊息，因為這些廣播訊息會持續存在，請改為在初始化時使用適當的
get方法來取得資訊。
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() 方法結尾取得 WifiP2pManager 的例項，並呼叫其 initialize() 方法。這個方法會傳回 WifiP2pManager.Channel 物件，您稍後會使用該物件將應用程式連線至 Wi-Fi Direct 架構。
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);
}
接下來，請建立新的 BroadcastReceiver 類別，用於監聽系統 Wi-Fi 狀態的變更。在 onReceive() 方法中，新增條件來處理上述各項狀態變更。
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));
}
}
最後，請新增程式碼，在主要活動啟用時註冊意圖篩選器和廣播接收器，並在活動暫停時取消註冊。最佳做法是使用 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);
}
啟動同儕探索
如要開始使用 Wi-Fi P2P 搜尋附近裝置，請呼叫 discoverPeers()。這個方法會使用下列引數：
- 初始化對等 mManager 時收到的
WifiP2pManager.Channel - 實作
WifiP2pManager.ActionListener的實作方式，其中包含系統在發現成功和失敗時會叫用的各個方法。
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.
}
});
請注意，這項操作只會啟動同儕探索功能。discoverPeers() 方法會啟動探索程序，然後立即傳回。如果透過呼叫提供的動作事件監聽器中的方法，成功啟動同端探索程序，系統會通知您。此外，發現功能會持續處於啟用狀態，直到建立連線或 P2P 群組為止。
擷取同儕清單
接下來，請編寫用於擷取及處理同儕清單的程式碼。首先，請實作 WifiP2pManager.PeerListListener 介面，該介面會提供 Wi-Fi Direct 偵測到的對等端資訊。這項資訊還可讓應用程式判斷對等端何時加入或離開網路。下列程式碼片段說明與同儕相關的這些作業：
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;
}
}
}
接著修改廣播接收器的 onReceive() 方法，以便在收到含有動作 WIFI_P2P_PEERS_CHANGED_ACTION 的意圖時呼叫 requestPeers()。您需要以某種方式將此事件監聽器傳遞至接收器。其中一種方法是將其當做引數傳送至廣播接收器的建構函式。
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");
}...
}
如今，含有 WIFI_P2P_PEERS_CHANGED_ACTION 動作的意圖會觸發要求更新的對等端清單。
連線至對等端
如要連線至對等端，請建立新的 WifiP2pConfig 物件，並從代表要連線裝置的 WifiP2pDevice 複製資料至該物件。然後呼叫 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();
}
});
}
如果群組中的每部裝置都支援 Wi-Fi 直連，您在連線時不需要明確要求群組密碼。不過，如要讓不支援 Wi-Fi Direct 的裝置加入群組，您必須呼叫 requestGroupInfo() 來擷取這個密碼，如以下程式碼片段所示：
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();
}
});
請注意，只有在啟動成功或失敗時，connect() 方法中實作的 WifiP2pManager.ActionListener 才會通知您。如要監聽連線狀態的變更，請實作 WifiP2pManager.ConnectionInfoListener 介面。當連線狀態變更時，其 onConnectionInfoAvailable() 回呼會通知您。如果有多部裝置要連線至單一部裝置 (例如有三個或更多玩家的遊戲，或聊天應用程式)，系統會指定一台裝置為「群組擁有者」。如要將特定裝置指定為網路的群組擁有者，請按照「建立群組」一節中的步驟操作。
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.
}
}
現在請返回廣播接收器的 onReceive() 方法，並修改用於監聽 WIFI_P2P_CONNECTION_CHANGED_ACTION 意圖的部分。收到此意圖時，請呼叫 requestConnectionInfo()。這是非同步呼叫，因此結果會由您以參數提供的連線資訊事件監聽器接收。
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);
}
...
建立群組
如果您希望執行應用程式的裝置可做為包含舊版裝置 (即不支援 Wi-Fi Direct 的裝置) 的網路群組擁有者，請按照「連線至對等裝置」一節中的步驟操作，但請使用 createGroup() 而非 connect() 建立新的 WifiP2pManager.ActionListener。WifiP2pManager.ActionListener 內的回呼處理方式相同，如以下程式碼片段所示：
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： 如果網路中的所有裝置都支援 Wi-Fi Direct，您可以在每部裝置上使用 connect() 方法，因為該方法會建立群組並自動選取群組擁有者。
建立群組後，您可以呼叫 requestGroupInfo() 來擷取網路上同端節點的詳細資料，包括裝置名稱和連線狀態。