Android 4.0引入了一项很重要的技术就是 WiFiDirect (WiFi直连) ，它可以让WiFi设备无需热点即可实现两个WiFi设备的P2P数据交换。使用最新的Android 4.0 SDK，最低API Level 14才支持此项技术，在SDK的例子中我们可以看到很多界面用到了Android 3.0时代的Fragment容器。

首先我们需要实现android.net.wifi.p2p.WifiP2pManager.ChannelListener 接口来获取支持WiFi直连的Android设备。

public class WiFiDirectActivity extends Activityimplements ChannelListener, DeviceActionListener {

public static final String TAG = "wifidirectdemo";
private WifiP2pManager manager;
private boolean isWifiP2pEnabled = false;
private boolean retryChannel = false;

private final IntentFilter intentFilter = new IntentFilter();
private Channel channel;
private BroadcastReceiver receiver = null;

public void setIsWifiP2pEnabled(boolean isWifiP2pEnabled) { //设置一个标记是否启用WiFi直连
this.isWifiP2pEnabled = isWifiP2pEnabled;
}

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

//注册所需要处理的action，比如WiFi连接、状态改变等。

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(Context.WIFI_P2P_SERVICE);
channel = manager.initialize(this, getMainLooper(), null); //实例化WifiP2pManager对象
}

@Override
public void onResume() {
super.onResume();
receiver = new WiFiDirectBroadcastReceiver(manager, channel, this);
registerReceiver(receiver, intentFilter);
}

@Override
public void onPause() {
super.onPause();
unregisterReceiver(receiver);
}

public void resetData() {
DeviceListFragment fragmentList = (DeviceListFragment) getFragmentManager()
.findFragmentById(R.id.frag_list);
DeviceDetailFragment fragmentDetails = (DeviceDetailFragment) getFragmentManager()
.findFragmentById(R.id.frag_detail);
if (fragmentList != null) {
fragmentList.clearPeers();
}
if (fragmentDetails != null) {
fragmentDetails.resetViews();
}
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.action_items, menu);
return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.atn_direct_enable:
if (manager != null && channel != null) {

startActivity(new Intent(Settings.ACTION_WIRELESS_SETTINGS));
} else {
Log.e(TAG, "channel or manager is null");
}
return true;

case R.id.atn_direct_discover:
if (!isWifiP2pEnabled) {
Toast.makeText(WiFiDirectActivity.this, R.string.p2p_off_warning,
Toast.LENGTH_SHORT).show();
return true;
}
final DeviceListFragment fragment = (DeviceListFragment) getFragmentManager()
.findFragmentById(R.id.frag_list);
fragment.onInitiateDiscovery();
manager.discoverPeers(channel, new WifiP2pManager.ActionListener() {

@Override
public void onSuccess() {
Toast.makeText(WiFiDirectActivity.this, "Discovery Initiated",
Toast.LENGTH_SHORT).show();
}

@Override
public void onFailure(int reasonCode) {
Toast.makeText(WiFiDirectActivity.this, "Discovery Failed : " + reasonCode,
Toast.LENGTH_SHORT).show();
}
});
return true;
default:
return super.onOptionsItemSelected(item);
}
}

@Override
public void showDetails(WifiP2pDevice device) {
DeviceDetailFragment fragment = (DeviceDetailFragment) getFragmentManager()
.findFragmentById(R.id.frag_detail);
fragment.showDetails(device);

}

@Override
public void connect(WifiP2pConfig config) {
manager.connect(channel, config, new ActionListener() {

@Override
public void onSuccess() {
// WiFiDirectBroadcastReceiver will notify us. Ignore for now.
}

@Override
public void onFailure(int reason) {
Toast.makeText(WiFiDirectActivity.this, "Connect failed. Retry.",
Toast.LENGTH_SHORT).show();
}
});
}

@Override
public void disconnect() {
final DeviceDetailFragment fragment = (DeviceDetailFragment) getFragmentManager()
.findFragmentById(R.id.frag_detail);
fragment.resetViews();
manager.removeGroup(channel, new ActionListener() {

@Override
public void onFailure(int reasonCode) {
Log.d(TAG, "Disconnect failed. Reason :" + reasonCode);

}

@Override
public void onSuccess() {
fragment.getView().setVisibility(View.GONE);
}

});
}

@Override
public void onChannelDisconnected() {
// we will try once more
if (manager != null && !retryChannel) {
Toast.makeText(this, "Channel lost. Trying again", Toast.LENGTH_LONG).show();
resetData();
retryChannel = true;
manager.initialize(this, getMainLooper(), this);
} else {
Toast.makeText(this,
"Severe! Channel is probably lost premanently. Try Disable/Re-Enable P2P.",
Toast.LENGTH_LONG).show();
}
}

@Override
public void cancelDisconnect() {

if (manager != null) {
final DeviceListFragment fragment = (DeviceListFragment) getFragmentManager()
.findFragmentById(R.id.frag_list);
if (fragment.getDevice() == null
|| fragment.getDevice().status == WifiP2pDevice.CONNECTED) {
disconnect();
} else if (fragment.getDevice().status == WifiP2pDevice.AVAILABLE
|| fragment.getDevice().status == WifiP2pDevice.INVITED) {

manager.cancelConnect(channel, new ActionListener() {

@Override
public void onSuccess() {
Toast.makeText(WiFiDirectActivity.this, "Aborting connection",
Toast.LENGTH_SHORT).show();
}

@Override
public void onFailure(int reasonCode) {
Toast.makeText(WiFiDirectActivity.this,
"Connect abort request failed. Reason Code: " + reasonCode,
Toast.LENGTH_SHORT).show();
}
});
}
}

}
}