本课程的第一课：使用网络服务 发现，为您显示了 如何发现连接到本地网络的服务。不过，如果使用 借助 Wi-Fi 直连（点对点）服务发现功能，您可以发现附近设备的服务 而无需连接到网络您还可以宣传这些服务 运行状态这些功能可帮助您在应用之间 即使没有可用的本地网络或热点也无妨。
虽然这组 API 在用途上与网络服务发现相似， 上一课中介绍的 API 和在代码中实现它们的方式截然不同。 本课将介绍如何发现其他设备提供的服务 使用 Wi-Fi 直连。本课假定您已熟悉 Wi-Fi Direct API。
设置清单
如需使用 Wi-Fi 点对点连接，请添加 CHANGE_WIFI_STATE、ACCESS_WIFI_STATE、
ACCESS_FINE_LOCATION,
和INTERNET
对清单的权限。如果您的应用以 Android 13（API 级别 33）或更高版本为目标平台，也请添加
NEARBY_WIFI_DEVICES,
权限。即使 Wi-Fi 直连不需要
连接互联网时，它使用标准 Java 套接字，并在 Android 中使用这些套接字
需要请求的权限。
<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" />
...
除上述权限外，以下 API 还要求启用位置信息模式：
添加本地服务
如果您提供本地服务，则需要注册该服务， 服务发现。注册本地服务后，框架 自动响应来自对等方的服务发现请求。
如需创建本地服务，请执行以下步骤：
- 创建
WifiP2pServiceInfo对象。 - 用您的服务相关信息填充该对象。
- 调用
addLocalService()以注册本地 服务发现。
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
}
});
}
发现附近的服务
Android 使用回调方法向您的应用通知可用服务，因此
首先需要进行设置创建 WifiP2pManager.DnsSdTxtRecordListener 以监听
传入的记录。此记录可以选择由其他方广播
设备。收到验证码后，请复制设备地址和任何其他
获取当前外部数据结构中所需的相关信息，
方法，以便稍后访问。以下示例假定
记录包含“buddyname”字段，填充了用户的身份信息。
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"));
}
};
}
如需获取服务信息，请创建一个 WifiP2pManager.DnsSdServiceResponseListener。这个
可接收实际的说明和连接信息。上一个代码
代码段实现了一个 Map 对象，用于将设备地址与好友配对
名称。服务响应监听器使用此参数将 DNS 记录与
相应的服务信息。将
监听器已实现，请使用 setDnsSdResponseListeners() 方法将它们添加到 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);
...
}
现在，创建一个服务请求并调用 addServiceRequest()。
此方法还会采用监听器报告成功或失败。
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
}
});
最后，调用 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(...)
...
}
});
如果一切进展顺利，您就大功告成了！如果您遇到问题，请记住
确保完成的异步调用
WifiP2pManager.ActionListener 作为参数，以及
这为您提供了指示成功或失败的回调。诊断
请将调试代码放在 onFailure() 中。错误代码
该方法提供的提示会提示问题。以下是可能的错误值
及其含义
-
P2P_UNSUPPORTED - 运行此应用的设备不支持 WLAN 直连。
-
BUSY - 系统太忙，无法处理请求。
-
ERROR - 由于内部错误，操作失败。