Add HomeVisibilityObserver APIs in ActivityManager.

The new API will be @System which is used by Telephony stk app to
monitor foreground activity change.

Bug: 144351078
Test: manual with a test app that registers HomeVisibilityObserver
and monitor its callback.
Change-Id: I2f250cdd53a667b2d89e84e589b0ae0bc94a8aa3

api/system-current.txt

@@ -327,10 +327,12 @@ package android.app {
     method @NonNull public java.util.Collection<java.util.Locale> getSupportedLocales();
     method @RequiresPermission(android.Manifest.permission.PACKAGE_USAGE_STATS) public int getUidImportance(int);
     method @RequiresPermission(android.Manifest.permission.KILL_UID) public void killUid(int, String);
+    method public void registerHomeVisibilityObserver(@NonNull android.app.HomeVisibilityObserver);
     method @RequiresPermission(android.Manifest.permission.PACKAGE_USAGE_STATS) public void removeOnUidImportanceListener(android.app.ActivityManager.OnUidImportanceListener);
     method public void setDeviceLocales(@NonNull android.os.LocaleList);
     method @RequiresPermission(android.Manifest.permission.RESTRICTED_VR_ACCESS) public static void setPersistentVrThread(int);
     method @RequiresPermission(android.Manifest.permission.MANAGE_USERS) public boolean switchUser(@NonNull android.os.UserHandle);
+    method public void unregisterHomeVisibilityObserver(@NonNull android.app.HomeVisibilityObserver);
     method @RequiresPermission(android.Manifest.permission.CHANGE_CONFIGURATION) public boolean updateMccMncConfiguration(@NonNull String, @NonNull String);
   }
 
@@ -579,6 +581,11 @@ package android.app {
     field public static final String ACTION_DOWNLOAD_COMPLETED = "android.intent.action.DOWNLOAD_COMPLETED";
   }
 
+  public abstract class HomeVisibilityObserver {
+    ctor public HomeVisibilityObserver();
+    method public abstract void onHomeVisibilityChanged(boolean);
+  }
+
   public abstract class InstantAppResolverService extends android.app.Service {
     ctor public InstantAppResolverService();
     method public final void attachBaseContext(android.content.Context);

core/java/android/app/ActivityManager.java

@@ -78,6 +78,7 @@ import com.android.internal.os.RoSystemProperties;
 import com.android.internal.os.TransferPipe;
 import com.android.internal.util.FastPrintWriter;
 import com.android.internal.util.MemInfoReader;
+import com.android.internal.util.Preconditions;
 import com.android.server.LocalServices;
 
 import org.xmlpull.v1.XmlSerializer;
@@ -4584,4 +4585,35 @@ public class ActivityManager {
             throw e.rethrowFromSystemServer();
         }
     }
+
+    /**
+     * Register with {@link HomeVisibilityObserver} with ActivityManager.
+     * @hide
+     */
+    @SystemApi
+    public void registerHomeVisibilityObserver(@NonNull HomeVisibilityObserver observer) {
+        Preconditions.checkNotNull(observer);
+        try {
+            observer.init(mContext, this);
+            getService().registerProcessObserver(observer.mObserver);
+            // Notify upon first registration.
+            observer.onHomeVisibilityChanged(observer.mIsHomeActivityVisible);
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
+
+    /**
+     * Unregister with {@link HomeVisibilityObserver} with ActivityManager.
+     * @hide
+     */
+    @SystemApi
+    public void unregisterHomeVisibilityObserver(@NonNull HomeVisibilityObserver observer) {
+        Preconditions.checkNotNull(observer);
+        try {
+            getService().unregisterProcessObserver(observer.mObserver);
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
 }

core/java/android/app/HomeVisibilityObserver.java

@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) 2020 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 android.app;
+
+import android.annotation.SystemApi;
+import android.content.Context;
+import android.content.Intent;
+import android.content.pm.PackageManager;
+import android.content.pm.ResolveInfo;
+
+import java.util.List;
+
+/**
+ * An observer / callback to create and register by
+ * {@link ActivityManager#registerHomeVisibilityObserver} so that it's triggered when
+ * visibility of home page changes.
+ * @hide
+ */
+@SystemApi
+public abstract class HomeVisibilityObserver {
+    private Context mContext;
+    private ActivityManager mActivityManager;
+    /** @hide */
+    IProcessObserver.Stub mObserver;
+    /** @hide */
+    boolean mIsHomeActivityVisible;
+
+    /** @hide */
+    void init(Context context, ActivityManager activityManager) {
+        mContext = context;
+        mActivityManager = activityManager;
+        mIsHomeActivityVisible = isHomeActivityVisible();
+    }
+
+    /**
+     * The API that needs implemented and will be triggered when activity on home page changes.
+     */
+    public abstract void onHomeVisibilityChanged(boolean isHomeActivityVisible);
+
+    public HomeVisibilityObserver() {
+        mObserver = new IProcessObserver.Stub() {
+            @Override
+            public void onForegroundActivitiesChanged(int pid, int uid, boolean fg) {
+                boolean isHomeActivityVisible = isHomeActivityVisible();
+                if (mIsHomeActivityVisible != isHomeActivityVisible) {
+                    mIsHomeActivityVisible = isHomeActivityVisible;
+                    onHomeVisibilityChanged(mIsHomeActivityVisible);
+                }
+            }
+
+            @Override
+            public void onForegroundServicesChanged(int pid, int uid, int fgServiceTypes) {
+            }
+
+            @Override
+            public void onProcessDied(int pid, int uid) {
+            }
+        };
+    }
+
+    private boolean isHomeActivityVisible() {
+        List<ActivityManager.RunningTaskInfo> tasks = mActivityManager.getRunningTasks(1);
+        if (tasks == null || tasks.isEmpty()) {
+            return false;
+        }
+
+        String top = tasks.get(0).topActivity.getPackageName();
+        if (top == null) {
+            return false;
+        }
+
+        // We can assume that the screen is idle if the home application is in the foreground.
+        final Intent intent = new Intent(Intent.ACTION_MAIN, null);
+        intent.addCategory(Intent.CATEGORY_HOME);
+
+        ResolveInfo info = mContext.getPackageManager().resolveActivity(intent,
+                PackageManager.MATCH_DEFAULT_ONLY);
+        if (info != null && top.equals(info.activityInfo.packageName)) {
+            return true;
+        }
+
+        return false;
+    }
+}