private static final String DEBUG_TAG = "NetworkStatusExample";
...
ConnectivityManager connMgr = (ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
boolean isWifiConn = networkInfo.isConnected();
networkInfo = connMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
boolean isMobileConn = networkInfo.isConnected();
Log.d(DEBUG_TAG, "Wifi connected: " + isWifiConn);
Log.d(DEBUG_TAG, "Mobile connected: " + isMobileConn);

public boolean isOnline() {
      ConnectivityManager connMgr = (ConnectivityManager)
      getSystemService(Context.CONNECTIVITY_SERVICE);
      NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
      return (networkInfo != null && networkInfo.isConnected());
}

<?xml version"utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.networkusage"
...>
<uses-sdk android:minSdkVersion="4"
android:targetSdkVersion="14" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<application
...>
...
<activity android:label".SettingsActivity">
<intent-filter>
<action android:name="android.intent.action.MANAGE_NETWORK_USAGE" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>

public class SettingsActivity extends PreferenceActivity implements OnSharedPreferenceChangeListener {
      @Override
      protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            // 加载XML设定文件(XML preferences file)
            addPreferencesFromResource(R.xml.preferences);
      }
      @Override
      protected void onResume() {
            super.onResume();
            // 每当键发生变化注册一个监听事件
            getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
      }
      @Override
      protected void onPause() {
            super.onPause();
            // 注销onResume()方法中设置的监听.  
            // 注销监听最好是当你的程序不使用它们以减少系统不���要的开销， 你可以在onPause()方法中做这件事        
            getPreferenceScreen().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
      }
      // 当用户改变设置的选项，onSharedPreferenceChanged()重新启动主activity作为一个新任务，
      // 设置refreshDisplay为true以表明主activity应该更新它的显示， 主activity查询PreferenceManager得到最新的设置.
      @Override
      public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            // 设置refreshDisplay为true，这样当用户返回主activity，显示会根据新设置进行刷新.
            NetworkActivity.refreshDisplay = true;
      }
}

public class NetworkActivity extends Activity {
      public static final String WIFI = "Wi-Fi";
      public static final String ANY = "Any";
      private static final String URL android&sort=newest";
      // 是否有一个Wi-Fi连接.
      private static boolean wifiConnected = false;
      // 是否有一个手机移动网络连接.
      private static boolean mobileConnected = false;
      // 显示是否需要刷新.
      public static boolean refreshDisplay = true;
      // 用户当前网络优先设置.
      public static String sPref = null;
      // BroadcastReceiver追踪网络连接变化.
      private NetworkReceiver receiver = new NetworkReceiver();
      @Override
      public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            // 注册BroadcastReceiver追踪网络连接变化.
            IntentFilter filter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
            receiver = new NetworkReceiver();
            this.registerReceiver(receiver, filter);
      }
      @Override
      public void onDestroy() {
            super.onDestroy();
            // 当应用销毁，注销BroadcastReceiver.
            if (receiver != null) {
                  this.unregisterReceiver(receiver);
            }
      }
      // 如果网络连接和优先设置允许，刷新显示。
      @Override
      public void onStart () {
            super.onStart();
            // 得到用户网络设置
            SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(this);
            // 获取设置的字符串，第二个参数为当获取不到设置的值时默认使用的值.
            sPref = sharedPrefs.getString("listPref", "Wi-Fi");
            updateConnectedFlags();
            if(refreshDisplay){
                  loadPage();
            }
      }
      // 检查网络连接并设置wifiConnected和mobileConnected变量. 
      public void updateConnectedFlags() {
            ConnectivityManager connMgr = (ConnectivityManager)
            getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo activeInfo = connMgr.getActiveNetworkInfo();
            if (activeInfo != null && activeInfo.isConnected()) {
                  wifiConnected = ConnectivityManager.TYPE_WIFI;
                  mobileConnected = ConnectivityManager.TYPE_MOBILE;
            } else {
            wifiConnected = false;
            mobileConnected = false;
      }
}
// 使用AsyncTask子类从stackoverflow.com下载XML数据源.
public void loadPage() {
      if (((sPref.equals(ANY)) && (wifiConnected || mobileConnected))
      || ((sPref.equals(WIFI)) && (wifiConnected))) {
            // AsyncTask的��类
            new DownloadXmlTask().execute(URL);
      } else {
      showErrorPage();
}
}
...
}

public class NetworkReceiver extends BroadcastReceiver {
      @Override
      public void onReceive(Context context, Intent intent) {
            ConnectivityManager conn = (ConnectivityManager)
            context.getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo = conn.getActiveNetworkInfo();
            // 检查用户首选项和网络连接.基于这个结果,决定刷新界面或保持当前显示.
            // 如果用户偏好Wi-Fi, 检查设备是否拥有Wi-Fi连接.
            if (WIFI.equals(sPref) && networkInfo != ConnectivityManager.TYPE_WIFI) {
                  // 如果设备有Wi-Fi连接,设置refreshDisplay为true
                  // 这是因为当用户返回到应用时，显示应该被刷新.
                  refreshDisplay = true;
                  Toast.makeText(context, R.string.wifi_connected, Toast.LENGTH_SHORT).show();
                  // 如果设置为任何网络并且这里有一个网络连接，设置refreshDisplay为true.
            } else if (ANY.equals(sPref) && networkInfo != null) {
                  refreshDisplay = true;
                  // 否则, 应用无法下载内容--可能是因为没有网络连接(mobile或Wi-Fi), 
                  // 或者是应为用户首选项是Wi-Fi，但没有Wi-Fi连接.设置refreshDisplay为false。
            } else {
            refreshDisplay = false;
            Toast.makeText(context, R.string.lost_connection, Toast.LENGTH_SHORT).show();
      }