本課程的第一堂課「使用網路服務探索功能」已說明如何探索連線至本機網路的服務。不過，使用 Wi-Fi Direct (P2P) 服務探索功能，您可以直接探索鄰近裝置的服務，而無須連線至網路。您也可以宣傳裝置上執行的服務。即使沒有可用的本機網路或無線基地台，這些功能仍可協助您在應用程式之間進行通訊。
雖然這組 API 的用途與上一課所述的網路服務探索 API 相似，但在程式碼中實作的方式卻截然不同。本課程將說明如何使用 Wi-Fi Direct 探索其他裝置提供的服務。本課程假設您已熟悉 Wi-Fi Direct API。
設定資訊清單
如要使用 Wi-Fi P2P，請將 CHANGE_WIFI_STATE、ACCESS_WIFI_STATE、ACCESS_FINE_LOCATION 和 INTERNET 權限新增至資訊清單。如果應用程式指定 Android 13 (API 級別 33) 以上版本，請一併將 NEARBY_WIFI_DEVICES 權限新增至資訊清單。雖然 Wi-Fi Direct 不需要網際網路連線，但會使用標準 Java 網路介面，因此在 Android 中使用這些網路介面需要要求權限。
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.nsdchat"
...
<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"/>
<!-- 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" />
...
除了上述權限之外，下列 API 也需要啟用位置模式：
新增本機服務
如果您提供本機服務，就必須註冊該服務，以便進行服務探索。當您註冊本機服務後，架構會自動回應來自同儕的服務探索要求。
如要建立本機服務，請按照下列步驟操作：
- 建立
WifiP2pServiceInfo物件。 - 填入服務相關資訊。
- 呼叫
addLocalService()即可註冊本機服務，以便進行服務探索。
Kotlin
private fun startRegistration() {
// Create a string map containing information about your service.
val record: Map<String, String> = mapOf(
"listenport" to SERVER_PORT.toString(),
"buddyname" to "John Doe${(Math.random() * 1000).toInt()}",
"available" to "visible"
)
// Service information. Pass it an instance name, service type
// _protocol._transportlayer , and the map containing
// information other devices will want once they connect to this one.
val serviceInfo =
WifiP2pDnsSdServiceInfo.newInstance("_test", "_presence._tcp", record)
// Add the local service, sending the service info, network channel,
// and listener that will be used to indicate success or failure of
// the request.
manager.addLocalService(channel, serviceInfo, object : WifiP2pManager.ActionListener {
override fun onSuccess() {
// Command successful! Code isn't necessarily needed here,
// Unless you want to update the UI or add logging statements.
}
override fun onFailure(arg0: Int) {
// Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
}
})
}
Java
private void startRegistration() {
// Create a string map containing information about your service.
Map record = new HashMap();
record.put("listenport", String.valueOf(SERVER_PORT));
record.put("buddyname", "John Doe" + (int) (Math.random() * 1000));
record.put("available", "visible");
// Service information. Pass it an instance name, service type
// _protocol._transportlayer , and the map containing
// information other devices will want once they connect to this one.
WifiP2pDnsSdServiceInfo serviceInfo =
WifiP2pDnsSdServiceInfo.newInstance("_test", "_presence._tcp", record);
// Add the local service, sending the service info, network channel,
// and listener that will be used to indicate success or failure of
// the request.
manager.addLocalService(channel, serviceInfo, new ActionListener() {
@Override
public void onSuccess() {
// Command successful! Code isn't necessarily needed here,
// Unless you want to update the UI or add logging statements.
}
@Override
public void onFailure(int arg0) {
// Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
}
});
}
發掘附近的服務
Android 會使用回呼方法通知應用程式可用的服務，因此您首先要做的就是設定這些服務。建立 WifiP2pManager.DnsSdTxtRecordListener 來監聽傳入的記錄。其他裝置可以選擇廣播這項記錄。收到訊息後，請將裝置位址和其他相關資訊複製到目前方法以外的資料結構中，以便日後存取。以下範例假設記錄包含「buddyname」欄位，並填入使用者的身分。
Kotlin
private val buddies = mutableMapOf<String, String>()
...
private fun discoverService() {
/* Callback includes:
* fullDomain: full domain name: e.g. "printer._ipp._tcp.local."
* record: TXT record dta as a map of key/value pairs.
* device: The device running the advertised service.
*/
val txtListener = DnsSdTxtRecordListener { fullDomain, record, device ->
Log.d(TAG, "DnsSdTxtRecord available -$record")
record["buddyname"]?.also {
buddies[device.deviceAddress] = it
}
}
}
Java
final HashMap<String, String> buddies = new HashMap<String, String>();
...
private void discoverService() {
DnsSdTxtRecordListener txtListener = new DnsSdTxtRecordListener() {
@Override
/* Callback includes:
* fullDomain: full domain name: e.g. "printer._ipp._tcp.local."
* record: TXT record dta as a map of key/value pairs.
* device: The device running the advertised service.
*/
public void onDnsSdTxtRecordAvailable(
String fullDomain, Map record, WifiP2pDevice device) {
Log.d(TAG, "DnsSdTxtRecord available -" + record.toString());
buddies.put(device.deviceAddress, record.get("buddyname"));
}
};
}
如要取得服務資訊，請建立 WifiP2pManager.DnsSdServiceResponseListener。這個事件會接收實際的說明和連結資訊。先前的程式碼程式碼片段實作了 Map 物件，將裝置位址與好友名稱配對。服務回應事件監聽器會使用這個值，將 DNS 記錄連結至相應的服務資訊。實作兩個事件監聽器後，請使用 setDnsSdResponseListeners() 方法將事件監聽器新增至 WifiP2pManager。
Kotlin
private fun discoverService() {
...
val servListener = DnsSdServiceResponseListener { instanceName, registrationType, resourceType ->
// Update the device name with the human-friendly version from
// the DnsTxtRecord, assuming one arrived.
resourceType.deviceName = buddies[resourceType.deviceAddress] ?: resourceType.deviceName
// Add to the custom adapter defined specifically for showing
// wifi devices.
val fragment = fragmentManager
.findFragmentById(R.id.frag_peerlist) as WiFiDirectServicesList
(fragment.listAdapter as WiFiDevicesAdapter).apply {
add(resourceType)
notifyDataSetChanged()
}
Log.d(TAG, "onBonjourServiceAvailable $instanceName")
}
manager.setDnsSdResponseListeners(channel, servListener, txtListener)
...
}
Java
private void discoverService() {
...
DnsSdServiceResponseListener servListener = new DnsSdServiceResponseListener() {
@Override
public void onDnsSdServiceAvailable(String instanceName, String registrationType,
WifiP2pDevice resourceType) {
// Update the device name with the human-friendly version from
// the DnsTxtRecord, assuming one arrived.
resourceType.deviceName = buddies
.containsKey(resourceType.deviceAddress) ? buddies
.get(resourceType.deviceAddress) : resourceType.deviceName;
// Add to the custom adapter defined specifically for showing
// wifi devices.
WiFiDirectServicesList fragment = (WiFiDirectServicesList) getFragmentManager()
.findFragmentById(R.id.frag_peerlist);
WiFiDevicesAdapter adapter = ((WiFiDevicesAdapter) fragment
.getListAdapter());
adapter.add(resourceType);
adapter.notifyDataSetChanged();
Log.d(TAG, "onBonjourServiceAvailable " + instanceName);
}
};
manager.setDnsSdResponseListeners(channel, servListener, txtListener);
...
}
接著，建立服務要求並呼叫 addServiceRequest()。這個方法也會使用事件監聽器來回報成功或失敗。
Kotlin
serviceRequest = WifiP2pDnsSdServiceRequest.newInstance()
manager.addServiceRequest(
channel,
serviceRequest,
object : WifiP2pManager.ActionListener {
override fun onSuccess() {
// Success!
}
override fun onFailure(code: Int) {
// Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
}
}
)
Java
serviceRequest = WifiP2pDnsSdServiceRequest.newInstance();
manager.addServiceRequest(channel,
serviceRequest,
new ActionListener() {
@Override
public void onSuccess() {
// Success!
}
@Override
public void onFailure(int code) {
// Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
}
});
最後，呼叫 discoverServices()。
Kotlin
manager.discoverServices(
channel,
object : WifiP2pManager.ActionListener {
override fun onSuccess() {
// Success!
}
override fun onFailure(code: Int) {
// Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
when (code) {
WifiP2pManager.P2P_UNSUPPORTED -> {
Log.d(TAG, "Wi-Fi Direct isn't supported on this device.")
}
}
}
}
)
Java
manager.discoverServices(channel, new ActionListener() {
@Override
public void onSuccess() {
// Success!
}
@Override
public void onFailure(int code) {
// Command failed. Check for P2P_UNSUPPORTED, ERROR, or BUSY
if (code == WifiP2pManager.P2P_UNSUPPORTED) {
Log.d(TAG, "Wi-Fi Direct isn't supported on this device.");
else if(...)
...
}
});
如果一切順利，恭喜你完成設定！如果遇到問題，請注意，您所做的非同步呼叫會將 WifiP2pManager.ActionListener 做為引數，並提供回呼，指出成功或失敗。如要診斷問題，請將偵錯程式碼放入 onFailure()。方法提供的錯誤代碼會暗示問題所在。以下是可能的錯誤值及其含義
-
P2P_UNSUPPORTED - 執行應用程式的裝置不支援 Wi-Fi Direct。
-
BUSY - 系統太忙，無法處理要求。
-
ERROR - 發生內部錯誤，因此作業失敗。