diff --git a/Android/app/build.gradle b/Android/app/build.gradle
index 91c4a06..5be388a 100644
--- a/Android/app/build.gradle
+++ b/Android/app/build.gradle
@@ -22,8 +22,8 @@ android {
         applicationId "tw.edu.kuas.wifiautologin"
         minSdkVersion 9
         targetSdkVersion 23
-        versionCode 220
-        versionName "2.2.0"
+        versionCode 221
+        versionName "2.2.1"
     }
     buildTypes {
         debug {
diff --git a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/MainActivity.java b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/MainActivity.java
index 6cbf726..be820a2 100644
--- a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/MainActivity.java
+++ b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/MainActivity.java
@@ -81,7 +81,6 @@ public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
 				PorterDuff.Mode.SRC_IN);
 
 		initGA();
-		Utils.forceUseWifi(this);
 	}
 
 	private void initGA() {
diff --git a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/WifiReceiver.java b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/WifiReceiver.java
index 67c13f7..e15c254 100644
--- a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/WifiReceiver.java
+++ b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/WifiReceiver.java
@@ -33,7 +33,6 @@ public void onReceive(final Context context, Intent intent) {
 		String action = intent.getAction();
 
 		if (action.equals(WifiManager.NETWORK_STATE_CHANGED_ACTION)) {
-			Utils.forceUseWifi(context);
 			initGA(context);
 
 			NetworkInfo networkInfo = intent.getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO);
@@ -60,14 +59,14 @@ public void onReceive(final Context context, Intent intent) {
 	private void login(Context context, UserModel model) {
 		LoginHelper.login(context, model, new GeneralCallback() {
 			@Override
-			public void onSuccess(final String message) {
+			public void onSuccess(String message) {
 				mTracker.send(
 						new HitBuilders.EventBuilder().setCategory("logout").setAction("success")
 								.setLabel(message).build());
 			}
 
 			@Override
-			public void onFail(final String reason) {
+			public void onFail(String reason) {
 				mTracker.send(new HitBuilders.EventBuilder().setCategory("logout").setAction("fail")
 						.setLabel(reason).build());
 			}
diff --git a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/callbacks/GeneralCallback.java b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/callbacks/GeneralCallback.java
index fe96d9f..19d4d70 100644
--- a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/callbacks/GeneralCallback.java
+++ b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/callbacks/GeneralCallback.java
@@ -1,6 +1,25 @@
 package tw.edu.kuas.wifiautologin.callbacks;
 
+import android.content.Context;
+
+import tw.edu.kuas.wifiautologin.libs.Utils;
+
 public abstract class GeneralCallback {
+	public void onSuccess(Context context, String message) {
+		Utils.resetDefaultNetwork(context);
+		onSuccess(message);
+	}
+
+	public void onFail(Context context, String reason) {
+		Utils.resetDefaultNetwork(context);
+		onFail(reason);
+	}
+
+	public void onAlready(Context context) {
+		Utils.resetDefaultNetwork(context);
+		onAlready();
+	}
+
 	public abstract void onSuccess(String message);
 
 	public abstract void onFail(String reason);
diff --git a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/libs/LoginHelper.java b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/libs/LoginHelper.java
index 27ec1f3..290c80a 100644
--- a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/libs/LoginHelper.java
+++ b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/libs/LoginHelper.java
@@ -44,11 +44,13 @@ private static void initGA(Context context) {
 	}
 
 	public static void login(final Context context, final UserModel model,
-	                         final GeneralCallback callback) {
+	                         @NonNull final GeneralCallback callback) {
 		if (!checkSSID(context, callback)) {
 			return;
 		}
 
+		Utils.requestNetwork(context);
+
 		final RequestBody requestBody =
 				new FormBody.Builder().add("username", model.username).add("userpwd", model.userpwd)
 						.add("login", "").add("orig_referer", "").build();
@@ -65,9 +67,7 @@ public void onFailure(Call call, IOException e) {
 			public void onResponse(Call call, Response response) {
 				call.cancel();
 				if (response.code() == 200) {
-					if (callback != null) {
-						callback.onAlready();
-					}
+					callback.onAlready(context);
 					if (!(context instanceof MainActivity)) {
 						NotificationHelper.createNotification(context,
 								context.getString(R.string.already_logged_in), false, false,
@@ -85,16 +85,14 @@ public void onResponse(Call call, Response response) {
 		});
 	}
 
-	private static boolean checkSSID(Context context, GeneralCallback callback) {
+	private static boolean checkSSID(Context context, @NonNull GeneralCallback callback) {
 		String ssid = Utils.getCurrentSSID(context);
 		if (TextUtils.isEmpty(ssid) || !Utils.isExpectedSSID(ssid)) {
-			if (callback != null) {
-				if (TextUtils.isEmpty(ssid)) {
-					callback.onFail(context.getString(R.string.no_wifi_connection));
-				} else {
-					callback.onFail(
-							String.format(context.getString(R.string.ssid_no_support), ssid));
-				}
+			if (TextUtils.isEmpty(ssid)) {
+				callback.onFail(context, context.getString(R.string.no_wifi_connection));
+			} else {
+				callback.onFail(context,
+						String.format(context.getString(R.string.ssid_no_support), ssid));
 			}
 			return false;
 		}
@@ -103,7 +101,7 @@ private static boolean checkSSID(Context context, GeneralCallback callback) {
 
 	private static void login(final Context context, final String location,
 	                          final UserModel.LoginType loginType, final RequestBody requestBody,
-	                          final GeneralCallback callback) {
+	                          @NonNull final GeneralCallback callback) {
 
 		String url = String.format(Locale.getDefault(), LOGIN_URL, location);
 
@@ -152,6 +150,7 @@ public static void logout(final Context context, final boolean recheck,
 			return;
 		}
 
+		Utils.requestNetwork(context);
 		initGA(context);
 
 		String url = String.format(Locale.getDefault(), TEST_LOGOUT_URL,
@@ -162,7 +161,7 @@ public static void logout(final Context context, final boolean recheck,
 		mClient.newCall(request).enqueue(new Callback() {
 			@Override
 			public void onFailure(Call call, IOException e) {
-				callback.onFail(context.getString(R.string.failed_to_logout));
+				callback.onFail(context, context.getString(R.string.failed_to_logout));
 			}
 
 			@Override
@@ -171,7 +170,7 @@ public void onResponse(Call call, Response response) {
 				if (response.code() == 302) {
 					checkLogoutLocation(context, response.header("location"), recheck, callback);
 				} else {
-					callback.onFail(context.getString(R.string.failed_to_logout));
+					callback.onFail(context, context.getString(R.string.failed_to_logout));
 				}
 			}
 		});
@@ -186,7 +185,7 @@ private static void checkLogoutLocation(Context context, String location, boolea
 			if (recheck) {
 				logout(context, false, callback);
 			} else {
-				callback.onAlready();
+				callback.onAlready(context);
 			}
 		} else {
 			mTracker.send(
@@ -207,13 +206,13 @@ private static void logout(final Context context, String location,
 		mClient.newCall(request).enqueue(new Callback() {
 			@Override
 			public void onFailure(Call call, IOException e) {
-				callback.onFail(context.getString(R.string.failed_to_logout));
+				callback.onFail(context, context.getString(R.string.failed_to_logout));
 			}
 
 			@Override
 			public void onResponse(Call call, Response response) {
 				if (response.code() == 200) {
-					callback.onSuccess(context.getString(R.string.logout_successful));
+					callback.onSuccess(context, context.getString(R.string.logout_successful));
 					NotificationHelper.cancelNotification(context, Constant.NOTIFICATION_LOGIN_ID);
 					NotificationHelper
 							.cancelNotification(context, Constant.NOTIFICATION_SUCCESS_ID);
@@ -221,7 +220,7 @@ public void onResponse(Call call, Response response) {
 					NotificationHelper
 							.cancelNotification(context, Constant.NOTIFICATION_ALREADY_ID);
 				} else {
-					callback.onFail(context.getString(R.string.failed_to_logout));
+					callback.onFail(context, context.getString(R.string.failed_to_logout));
 				}
 			}
 		});
@@ -237,7 +236,8 @@ private static void showLoginNotification(Context context, UserModel.LoginType l
 	}
 
 	private static void loginSuccess(Context context, String location,
-	                                 UserModel.LoginType loginType, GeneralCallback callback) {
+	                                 UserModel.LoginType loginType,
+	                                 @NonNull GeneralCallback callback) {
 		String campus = location.equals(Constant.JIANGONG_WIFI_SERVER) ?
 				context.getString(R.string.jiangong) : context.getString(R.string.yanchao);
 		String result;
@@ -265,16 +265,13 @@ private static void loginSuccess(Context context, String location,
 		NotificationHelper.cancelNotification(context, Constant.NOTIFICATION_FAIL_ID);
 		NotificationHelper.cancelNotification(context, Constant.NOTIFICATION_ALREADY_ID);
 
-		if (callback != null) {
-			callback.onSuccess(result);
-		}
+		callback.onSuccess(context, result);
 	}
 
-	private static void loginFail(Context context, String reason, GeneralCallback callback) {
+	private static void loginFail(Context context, String reason,
+	                              @NonNull GeneralCallback callback) {
 		NotificationHelper.cancelNotification(context, Constant.NOTIFICATION_LOGIN_ID);
-		if (callback != null) {
-			callback.onFail(reason);
-		}
+		callback.onFail(context, reason);
 		if (!(context instanceof MainActivity)) {
 			NotificationHelper.createNotification(context, reason, false, true,
 					Constant.NOTIFICATION_FAIL_ID);
diff --git a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/libs/Utils.java b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/libs/Utils.java
index c501fae..83da980 100644
--- a/Android/app/src/main/java/tw/edu/kuas/wifiautologin/libs/Utils.java
+++ b/Android/app/src/main/java/tw/edu/kuas/wifiautologin/libs/Utils.java
@@ -10,11 +10,15 @@
 import android.net.wifi.WifiManager;
 import android.os.Build;
 import android.text.TextUtils;
+import android.util.Log;
 
 import tw.edu.kuas.wifiautologin.models.UserModel;
 
 public class Utils {
 
+	private static ConnectivityManager.NetworkCallback mCallback;
+	private static ConnectivityManager mConnectivityManager;
+
 	public static String getCurrentSSID(Context context) {
 		WifiManager wifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
 		WifiInfo wifiInfo = wifiManager.getConnectionInfo();
@@ -72,26 +76,73 @@ public static UserModel tranUser(String user, String pwd) {
 		return model;
 	}
 
-	@TargetApi(21)
-	public static void forceUseWifi(Context context) {
-		if (!Utils.postVersion(21)) {
+	@TargetApi(Build.VERSION_CODES.LOLLIPOP)
+	public static void requestNetwork(Context context) {
+		if (!Utils.postVersion(Build.VERSION_CODES.LOLLIPOP)) {
 			return;
 		}
-		final ConnectivityManager cm =
-				(ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
-		NetworkRequest.Builder req = new NetworkRequest.Builder();
-		req.addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET);
-		req.addTransportType(NetworkCapabilities.TRANSPORT_WIFI);
-		cm.requestNetwork(req.build(), new ConnectivityManager.NetworkCallback() {
+
+		setUpConnectivityManager(context);
+		NetworkRequest.Builder builder = new NetworkRequest.Builder();
+		builder.addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET);
+		builder.addTransportType(NetworkCapabilities.TRANSPORT_WIFI);
+
+		if (mCallback != null) {
+			try {
+				mConnectivityManager.unregisterNetworkCallback(mCallback);
+			} catch (IllegalArgumentException e) {
+				e.printStackTrace();
+			}
+		}
+		mCallback = new ConnectivityManager.NetworkCallback() {
 			@Override
 			public void onAvailable(Network network) {
-				if (Utils.postVersion(23)) {
-					cm.bindProcessToNetwork(network);
-				} else {
-					ConnectivityManager.setProcessDefaultNetwork(network);
+				if (mCallback != null) {
+					Log.d(Constant.TAG, network.toString());
+					if (Utils.postVersion(Build.VERSION_CODES.M)) {
+						mConnectivityManager.bindProcessToNetwork(network);
+					} else {
+						ConnectivityManager.setProcessDefaultNetwork(network);
+					}
 				}
 			}
-		});
+		};
+
+		mConnectivityManager.requestNetwork(builder.build(), mCallback);
+	}
+
+	@TargetApi(Build.VERSION_CODES.LOLLIPOP)
+	public static void resetDefaultNetwork(Context context) {
+		if (!Utils.postVersion(Build.VERSION_CODES.LOLLIPOP)) {
+			return;
+		}
+
+		setUpConnectivityManager(context);
+		if (Utils.postVersion(Build.VERSION_CODES.M)) {
+			if (mConnectivityManager.getBoundNetworkForProcess() != null) {
+				mConnectivityManager.bindProcessToNetwork(null);
+			}
+		} else {
+			if (ConnectivityManager.getProcessDefaultNetwork() != null) {
+				ConnectivityManager.setProcessDefaultNetwork(null);
+			}
+		}
+
+		if (mCallback != null) {
+			try {
+				mConnectivityManager.unregisterNetworkCallback(mCallback);
+			} catch (IllegalArgumentException e) {
+				e.printStackTrace();
+			}
+		}
+		mCallback = null;
+	}
+
+	private static void setUpConnectivityManager(Context context) {
+		if (mConnectivityManager == null) {
+			mConnectivityManager =
+					(ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
+		}
 	}
 
 	public static boolean postVersion(int sdkInt) {