Move HideNonSystemOverlayMixin to SettingsLib

To be re-used by settings applications for other form factors.

Bug: 184967544
Test: make RunSettingsLibRoboTests -j40
ROBOTEST_FILTER=com.android.settingslib.core.lifecycle

Change-Id: I749dbd3f24bf77453d3ecc5d4374d11656498850

packages/SettingsLib/src/com/android/settingslib/core/lifecycle/HideNonSystemOverlayMixin.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright (C) 2021 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.settingslib.core.lifecycle;
+
+import static android.view.WindowManager.LayoutParams.SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS;
+
+import static androidx.lifecycle.Lifecycle.Event.ON_START;
+import static androidx.lifecycle.Lifecycle.Event.ON_STOP;
+
+import android.app.Activity;
+import android.provider.Settings;
+import android.view.Window;
+import android.view.WindowManager;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.lifecycle.LifecycleObserver;
+import androidx.lifecycle.OnLifecycleEvent;
+
+/**
+ * A mixin that adds window flag to prevent non-system overlays showing on top of Settings
+ * activities.
+ */
+public class HideNonSystemOverlayMixin implements LifecycleObserver {
+
+    public static final String SECURE_OVERLAY_SETTINGS = "secure_overlay_settings";
+
+    private final Activity mActivity;
+
+    public HideNonSystemOverlayMixin(Activity activity) {
+        mActivity = activity;
+    }
+
+    @VisibleForTesting
+    boolean isEnabled() {
+        return Settings.Secure.getInt(mActivity.getContentResolver(),
+                SECURE_OVERLAY_SETTINGS, 0 /* defValue */) == 0;
+    }
+
+    /**
+     * Start Lifecycle event
+     */
+    @OnLifecycleEvent(ON_START)
+    public void onStart() {
+        if (mActivity == null || !isEnabled()) {
+            return;
+        }
+        mActivity.getWindow().addSystemFlags(SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS);
+        android.util.EventLog.writeEvent(0x534e4554, "120484087", -1, "");
+    }
+
+    /**
+     * Stop Lifecycle event
+     */
+    @OnLifecycleEvent(ON_STOP)
+    public void onStop() {
+        if (mActivity == null || !isEnabled()) {
+            return;
+        }
+        final Window window = mActivity.getWindow();
+        final WindowManager.LayoutParams attrs = window.getAttributes();
+        attrs.privateFlags &= ~SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS;
+        window.setAttributes(attrs);
+    }
+}

packages/SettingsLib/tests/robotests/src/com/android/settingslib/core/lifecycle/HideNonSystemOverlayMixinTest.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright (C) 2021 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.settingslib.core.lifecycle;
+
+import static android.view.WindowManager.LayoutParams.SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS;
+
+import static com.android.settingslib.core.lifecycle.HideNonSystemOverlayMixin.SECURE_OVERLAY_SETTINGS;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.os.Bundle;
+import android.provider.Settings;
+import android.view.WindowManager;
+
+import androidx.annotation.Nullable;
+import androidx.appcompat.app.AppCompatActivity;
+
+import com.android.settingslib.R;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.Robolectric;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.android.controller.ActivityController;
+
+@RunWith(RobolectricTestRunner.class)
+public class HideNonSystemOverlayMixinTest {
+
+    private ActivityController<TestActivity> mActivityController;
+
+    @Before
+    public void setUp() {
+        mActivityController = Robolectric.buildActivity(TestActivity.class);
+    }
+
+    @Test
+    public void startActivity_shouldHideNonSystemOverlay() {
+        mActivityController.setup();
+        TestActivity activity = mActivityController.get();
+
+        // Activity start: HIDE_NON_SYSTEM_OVERLAY should be set.
+        final WindowManager.LayoutParams attrs = activity.getWindow().getAttributes();
+        assertThat(attrs.privateFlags & SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS)
+                .isNotEqualTo(0);
+    }
+
+    @Test
+    public void stopActivity_shouldUnhideNonSystemOverlay() {
+        mActivityController.setup().stop();
+        TestActivity activity = mActivityController.get();
+
+        final WindowManager.LayoutParams attrs = activity.getWindow().getAttributes();
+        assertThat(attrs.privateFlags & SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS)
+                .isEqualTo(0);
+    }
+
+    @Test
+    public void isEnabled_isAllowedOverlaySettings_returnFalse() {
+        mActivityController.setup();
+        final TestActivity activity = mActivityController.get();
+        Settings.Secure.putInt(activity.getContentResolver(),
+                SECURE_OVERLAY_SETTINGS, 1);
+
+        assertThat(new HideNonSystemOverlayMixin(activity).isEnabled()).isFalse();
+    }
+
+    @Test
+    public void isEnabled_isNotAllowedOverlaySettings_returnTrue() {
+        mActivityController.setup();
+        TestActivity activity = mActivityController.get();
+        Settings.Secure.putInt(activity.getContentResolver(),
+                SECURE_OVERLAY_SETTINGS, 0);
+
+        assertThat(new HideNonSystemOverlayMixin(activity).isEnabled()).isTrue();
+    }
+
+    public static class TestActivity extends AppCompatActivity {
+        @Override
+        protected void onCreate(@Nullable Bundle savedInstanceState) {
+            super.onCreate(savedInstanceState);
+            setTheme(R.style.Theme_AppCompat);
+            getLifecycle().addObserver(new HideNonSystemOverlayMixin(this));
+        }
+    }
+}