本课程的第一课，使用网络服务发现，向您展示了如何发现连接到本地网络的服务。但是，使用 Wi-Fi Direct (P2P) 服务发现允许您直接发现附近设备的服务，而无需连接到网络。您还可以宣传您的设备上运行的服务。这些功能可以帮助您在应用程序之间进行通信，即使没有可用的本地网络或热点。
虽然这组 API 在目的上与之前课程中概述的网络服务发现 API 类似，但它们在代码中的实现方式却大不相同。本课程将向您展示如何使用 Wi-Fi Direct 发现其他设备提供的服务。本课程假设您已经熟悉 Wi-Fi Direct API。
设置清单
为了使用 Wi-Fi P2P，请将 CHANGE_WIFI_STATE、ACCESS_WIFI_STATE、ACCESS_FINE_LOCATION 和 INTERNET 权限添加到您的清单中。如果您的应用程序面向 Android 13（API 级别 33）或更高版本，请将 NEARBY_WIFI_DEVICES 权限添加到您的清单中。尽管 Wi-Fi Direct 不需要互联网连接，但它使用标准 Java 套接字，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" />
...
除了上述权限外，以下 API 还需要启用位置模式
添加本地服务
如果您提供本地服务，则需要为服务发现注册该服务。注册本地服务后，框架会自动响应来自对等方的服务发现请求。
要创建本地服务，请执行以下操作
- 创建一个
WifiP2pServiceInfo对象。 - 用有关您的服务的信息填充它。
- 调用
addLocalService()注册本地服务，以便进行服务发现。
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 使用回调方法来通知您的应用程序可用服务，因此第一步是设置回调。创建一个 WifiP2pManager.DnsSdTxtRecordListener 来监听传入的记录。此记录可以选择由其他设备广播。当接收到记录时，将设备地址和您需要的任何其他相关信息复制到当前方法外部的数据结构中，以便您以后可以访问它。以下示例假设记录包含一个名为“buddyname”的字段，其中填充了用户标识。
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"));
}
};
}
要获取服务信息，请创建一个 WifiP2pManager.DnsSdServiceResponseListener。这将接收实际的描述和连接信息。之前的代码片段实现了一个 Map 对象，用于将设备地址与好友姓名配对。服务响应监听器使用此方法将 DNS 记录与相应的服务信息关联起来。实现这两个监听器后，使用 setDnsSdResponseListeners() 方法将它们添加到 WifiP2pManager 中。
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()。此方法还会使用监听器来报告成功或失败。
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(...)
...
}
});
如果一切顺利，恭喜！您已经完成了！如果您遇到问题，请记住您进行的异步调用会将 WifiP2pManager.ActionListener 作为参数，并且它会提供指示成功或失败的回调。要诊断问题，请在 onFailure() 中添加调试代码。方法提供的错误代码暗示了问题所在。以下是可能的错误值及其含义：
-
P2P_UNSUPPORTED - 运行应用程序的设备不支持 Wi-Fi Direct。
-
BUSY - 系统太忙，无法处理请求。
-
ERROR - 操作因内部错误而失败。