[Setting] MobileNetwork UI performance

1. Create a singleton to reduce number of SubscriptionManager accessing
2. Listening to Airplane mode change to clear cache value

Bug: 141833767
Test: Manual
make RunSettingsRoboTests -j ROBOTEST_FILTER=MobileNetworkActivityTest
make RunSettingsRoboTests -j ROBOTEST_FILTER=GlobalSettingsChangeListenerTest

Change-Id: Icd76fd9bcef7a7822400bfe42b0d40f5bd920eed

tests/robotests/src/com/android/settings/network/GlobalSettingsChangeListenerTest.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.network;
+
+import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+import android.content.Context;
+import android.provider.Settings;
+
+import androidx.lifecycle.Lifecycle;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.RuntimeEnvironment;
+
+@RunWith(RobolectricTestRunner.class)
+public class GlobalSettingsChangeListenerTest {
+
+    @Mock
+    private Lifecycle mLifecycle;
+
+    private Context mContext;
+    private GlobalSettingsChangeListener mListener;
+
+    private static final String SETTINGS_FIELD = Settings.Global.AIRPLANE_MODE_ON;
+
+    @Before
+    public void setUp() {
+        MockitoAnnotations.initMocks(this);
+        mContext = spy(RuntimeEnvironment.application);
+        mListener = spy(new GlobalSettingsChangeListener(mContext, SETTINGS_FIELD) {
+            public void onChanged(String field) {}
+        });
+
+        doNothing().when(mLifecycle).addObserver(mListener);
+        doNothing().when(mLifecycle).removeObserver(mListener);
+    }
+
+    @Test
+    public void whenChanged_onChangedBeenCalled() {
+        mListener.onChange(false);
+        verify(mListener, times(1)).onChanged(SETTINGS_FIELD);
+    }
+
+    @Test
+    public void whenNotifyChangeBasedOnLifecycle_onStopEvent_onChangedNotCalled() {
+        mListener.notifyChangeBasedOn(mLifecycle);
+        mListener.onStart();
+
+        mListener.onChange(false);
+        verify(mListener, times(1)).onChanged(SETTINGS_FIELD);
+
+        mListener.onStop();
+
+        mListener.onChange(false);
+        verify(mListener, times(1)).onChanged(SETTINGS_FIELD);
+
+        mListener.onStart();
+
+        mListener.onChange(false);
+        verify(mListener, times(2)).onChanged(SETTINGS_FIELD);
+    }
+}