我尝试在Android上使用WiFi Direct开发聊天应用程序，我试图在Android的WiFiServiceDiscovery样本上构建我的应用程序：
https://android.googlesource.com/platform/development/+/d4a1f0619bc6a83d75c7b6686f9015eb7b3cec6c/samples/WiFiDirectServiceDiscovery/src/com/example/android/wifidirect/discovery
问题是我希望将WiFiServiceDiscoveryActivity转换为Android服务，因此即使应用程序已关闭/暂停，它也可以运行发现对等方并通知用户
所以我试着把它变成Android服务：
public class ConnectAndDiscoverService extends Service implements Handler.Callback, WifiP2pManager.ConnectionInfoListener,WiFiDirectServicesFragment.DeviceClickListener{
/*
*Service attributes
*/
public static final String TXTRECORD_PROP_AVAILABLE = "available";
//Our service's name and protocol
public static final String SERVICE_NAME = "_vicinityapp";
public static final String SERVICE_REG_TYPE = "_presence._tcp";
static final int SERVER_PORT = 4142;
public static final int MESSAGE_READ = 0x400 + 1;
public static final int MY_HANDLE = 0x400 + 2;
private WifiP2pManager manager;
private final IntentFilter intentFilter = new IntentFilter();
private Channel channel;
private BroadcastReceiver receiver = null;
private WifiP2pDnsSdServiceRequest serviceRequest;
private Handler handler = new Handler(this);
public Handler getHandler(){
return this.handler;
}
public void setHandler(Handler handler) {
this.handler = handler;
}
public ConnectAndDiscoverService() {
Log.i(TAG,"Service started");
intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);
intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);
intentFilter
.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);
intentFilter
.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);
manager = (WifiP2pManager) getSystemService(WIFI_P2P_SERVICE);
channel = manager.initialize(this, getMainLooper(), null);
startRegistrationAndDiscovery();
// servicesList = new WiFiDirectServicesList();
// getFragmentManager().beginTransaction()
// .add(R.id.container_root, servicesList, "services").commit();
}
@Override
public IBinder onBind(Intent intent) {
Log.i(TAG, "onBind");
throw new UnsupportedOperationException("Not yet implemented");
}
/**
* This method adds _vicinityapp local service to the network
* then calls discoverService()
*/
private void startRegistrationAndDiscovery() {
Log.i(TAG,"startRegistrationAndDiscovery");
Map<String, String> record = new HashMap<String, String>();
record.put(TXTRECORD_PROP_AVAILABLE, "visible");
//WifiP2pDnsSdServiceInfo is A class for storing Bonjour service information that is advertised over a Wi-Fi peer-to-peer setup.
WifiP2pDnsSdServiceInfo service = WifiP2pDnsSdServiceInfo.newInstance(SERVICE_NAME, SERVICE_REG_TYPE, record);
//addLocalService Registers our service as a local service in order to be discovered.
manager.addLocalService(channel, service, new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
//What to do if our service got advertised in the local network
Log.i(TAG,"_vicinityapp Service registered");
}
@Override
public void onFailure(int error) {
Log.i(TAG,"Failed to add a service");
}
});
discoverService();
}
/**
*First discoverService() registers listeners for DNS-SD services
* Then it creates a service discovery request and initiates service discovery
*/
private void discoverService() {
Log.i(TAG,"discoverService");
//setDnsSdResponseListeners() Registers a callback to be invoked on receiving Bonjour service discovery response.
manager.setDnsSdResponseListeners(channel,
new WifiP2pManager.DnsSdServiceResponseListener() {
@Override
public void onDnsSdServiceAvailable(String instanceName,
String registrationType, WifiP2pDevice srcDevice) {
// A service has been discovered here, we need to see if it's our app.
if (instanceName.equalsIgnoreCase(SERVICE_NAME)) {
// update the UI and add the item the discovered
// device.
/*WiFiDirectServicesList fragment = (WiFiDirectServicesList) getFragmentManager()
.findFragmentByTag("services");
if (fragment != null) {
WiFiDirectServicesList.WiFiDevicesAdapter adapter = ((WiFiDirectServicesList.WiFiDevicesAdapter) fragment
.getListAdapter());
WiFiP2pService service = new WiFiP2pService();
service.device = srcDevice;
service.instanceName = instanceName;
service.serviceRegistrationType = registrationType;
adapter.add(service);
adapter.notifyDataSetChanged();
Log.d(TAG, "onBonjourServiceAvailable "
+ instanceName);
}*/
}
}
}, new WifiP2pManager.DnsSdTxtRecordListener() {
/*
* A new TXT record is available. Pick up the advertised
* buddy name.
*/
@Override
public void onDnsSdTxtRecordAvailable(
String fullDomainName, Map<String, String> record,
WifiP2pDevice device) {
Log.d(TAG,
device.deviceName + " is "
+ record.get(TXTRECORD_PROP_AVAILABLE));
}
});
//1. Add a service discovery request: addServiceRequest()
serviceRequest = WifiP2pDnsSdServiceRequest.newInstance();
manager.addServiceRequest(channel, serviceRequest,
new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
Log.i(TAG,"Added service discovery request");
}
@Override
public void onFailure(int arg0) {
Log.i(TAG,"Failed adding service discovery request");
}
});
//2. Initiating service discovery.
manager.discoverServices(channel, new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
Log.i(TAG, "Service discovery initiated");
}
@Override
public void onFailure(int arg0) {
Log.i(TAG, "Service discovery failed");
}
});
}//end of discoverServices
/**
*
* @param msg
* @return
*/
@Override
public boolean handleMessage(Message msg) {
switch (msg.what) {
case MESSAGE_READ:
byte[] readBuf = (byte[]) msg.obj;
// construct a string from the valid bytes in the buffer
String readMessage = new String(readBuf, 0, msg.arg1);
Log.d(TAG, readMessage);
// (chatFragment).pushMessage("Buddy: " + readMessage);
break;
case MY_HANDLE:
Object obj = msg.obj;
// (chatFragment).setChatManager((ChatManager) obj);
}
return true;
}
/**
* This method connects peers with each other
* @param service the service you want to connect to
*/
@Override
public void connectP2p(WiFiP2pService service) {
Log.i(TAG,"connectP2P");
//Wi-Fi P2p configuration for setting up a connection
WifiP2pConfig config = new WifiP2pConfig();
config.deviceAddress = service.device.deviceAddress;//device unique MAC address
config.wps.setup = WpsInfo.PBC;
if (serviceRequest != null)
manager.removeServiceRequest(channel, serviceRequest,
new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
}
@Override
public void onFailure(int arg0) {
}
});
manager.connect(channel, config, new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
Log.i(TAG,"Connecting to service");
}
@Override
public void onFailure(int errorCode) {
Log.i(TAG,"Failed connecting to service");
}
});
}
/**
* After connecting to a P2P group this method is invoked
* @param p2pInfo
*/
@Override
public void onConnectionInfoAvailable(WifiP2pInfo p2pInfo) {
Log.i(TAG,"onConnectionAvailable");
Thread handler = null;
/*
* The group owner accepts connections using a server socket and then spawns a
* client socket for every client. This is handled by {@code
* GroupOwnerSocketHandler}
if (p2pInfo.isGroupOwner) {
Log.i(TAG, "Connected as group owner");
try {
handler = new GroupOwnerSocketHandler(
((MessageTarget) this).getHandler());
handler.start();
} catch (IOException e) {
Log.d(TAG,"Failed to create a server thread - " + e.getMessage());
return;
}
} else {
Log.d(TAG, "Connected as peer");
handler = new ClientSocketHandler(
((MessageTarget) this).getHandler(),
p2pInfo.groupOwnerAddress);
handler.start();
}
chatFragment = new WiFiChatFragment();
getFragmentManager().beginTransaction()
.replace(R.id.container_root, chatFragment).commit();
statusTxtView.setVisibility(View.GONE);*/
}
/**
* This method changes the original device name
* to the user's username
* @param username registered username
*/
public void changeDeviceName(String username){
try{
Log.i(TAG,"Changing name!!");
Method m = manager.getClass().getMethod(
"setDeviceName",
new Class[] { WifiP2pManager.Channel.class, String.class,
WifiP2pManager.ActionListener.class });
m.invoke(manager,channel, "AFNAN", new WifiP2pManager.ActionListener() {
public void onSuccess() {
//Code for Success in changing name
}
public void onFailure(int reason) {
//Code to be done while name change Fails
}
});
}
catch(Exception e){
}
}
}
由于这行，我从另一个活动启动服务时会导致NullPointerException：
manager = (WifiP2pManager) getSystemService(WIFI_P2P_SERVICE);
答案 0 :(得分：0)
你得到一个NullPointerException，因为它试图在没有已知上下文的情况下调用getSystemService（调用实际上应该是context.getSystemService(...)）。
要在服务中使用getSystemService，您需要以某种方式从创建和/或使用服务的活动或片段传递上下文。