ADD: Utility class UserHandles.

library/src/main/java/com/oasisfeng/android/annotation/UserIdInt.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2016 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.oasisfeng.android.annotation;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PARAMETER;
+import static java.lang.annotation.RetentionPolicy.SOURCE;
+
+/**
+ * Denotes that the annotated element is a multi-user user ID. This is
+ * <em>not</em> the same as a UID.
+ */
+@Retention(SOURCE)
+@Target({METHOD, PARAMETER, FIELD})
+public @interface UserIdInt {
+}

library/src/main/java/com/oasisfeng/android/os/UserHandles.java

@@ -0,0 +1,68 @@
+package com.oasisfeng.android.os;
+
+import android.os.Parcel;
+import android.os.UserHandle;
+import android.util.Pair;
+
+import com.oasisfeng.android.annotation.UserIdInt;
+
+import static android.os.Build.VERSION.SDK_INT;
+import static android.os.Build.VERSION_CODES.N;
+
+/**
+ * Created by Oasis on 2018-9-6.
+ */
+public class UserHandles {
+
+	private static Pair<Integer, UserHandle> sCache = null;	// Must before SYSTEM
+
+	/**
+	 * Enable multi-user related side effects. Set this to false if
+	 * there are problems with single user use-cases.
+	 */
+	private static final boolean MU_ENABLED = true;
+
+	/**
+	 * Range of uids allocated for a user.
+	 */
+	public static final int PER_USER_RANGE = 100000;
+
+	/** A user id constant to indicate the "system" user of the device */
+	public static final @UserIdInt int USER_SYSTEM = 0;
+
+	/** A user handle to indicate the "system" user of the device */
+	public static final UserHandle SYSTEM = of(USER_SYSTEM);
+
+	public static UserHandle getUserHandleForUid(final int uid) {
+		return SDK_INT >= N ? UserHandle.getUserHandleForUid(uid) : of(getUserId(uid));
+	}
+
+	public static UserHandle of(final @UserIdInt int userId) {
+		if (userId == USER_SYSTEM) return SYSTEM;
+		final Pair<Integer, UserHandle> cache = sCache;
+		if (cache != null && cache.first == userId) return cache.second;
+
+		final Parcel parcel = Parcel.obtain();
+		try {
+			final int begin = parcel.dataPosition();
+			parcel.writeInt(userId);
+			parcel.setDataPosition(begin);
+			final UserHandle user = UserHandle.CREATOR.createFromParcel(parcel);
+			sCache = new Pair<>(userId, user);
+			return user;
+		} finally {
+			parcel.recycle();
+		}
+	}
+
+	/**
+	 * Returns the user id for a given uid.
+	 */
+	public static @UserIdInt int getUserId(final int uid) {
+		if (MU_ENABLED) {
+			return uid / PER_USER_RANGE;
+		} else {
+			return USER_SYSTEM;
+		}
+	}
+}