1/*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
5 * use this file except in compliance with the License. You may obtain a copy
6 * of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16package android.content.res;
17
18import android.annotation.AnyRes;
19
20/**
21 * Provides a set of utility methods for dealing with Resource IDs.
22 * @hide
23 */
24public final class ResourceId {
25
26    /**
27     * The {@code null} resource ID.
28     */
29    public static final @AnyRes int ID_NULL = 0;
30
31    /**
32     * Checks whether the integer {@code id} is a valid resource ID, as generated by AAPT.
33     * <p>Note that a negative integer is not necessarily an invalid resource ID, and custom
34     * validations that compare the {@code id} against {@code 0} are incorrect.</p>
35     * @param id The integer to validate.
36     * @return {@code true} if the integer is a valid resource ID.
37     */
38    public static boolean isValid(@AnyRes int id) {
39        // With the introduction of packages with IDs > 0x7f, resource IDs can be negative when
40        // represented as a signed Java int. Some legacy code assumes -1 is an invalid resource ID,
41        // despite the existing documentation.
42        return id != -1 && (id & 0xff000000) != 0 && (id & 0x00ff0000) != 0;
43    }
44}
45