SectionIndexer.java revision 5add56ec49cef52db7ebd3006665f318a5d16dd3 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy 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,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.widget;
18
19/**
20 * Interface that should be implemented on Adapters to enable fast scrolling
21 * in an {@link AbsListView} between sections of the list. A section is a group of list items
22 * to jump to that have something in common. For example, they may begin with the
23 * same letter or they may be songs from the same artist. ExpandableListAdapters that
24 * consider groups and sections as synonymous should account for collapsed groups and return
25 * an appropriate section/position.
26 */
27public interface SectionIndexer {
28    /**
29     * This provides the list view with an array of section objects. In the simplest
30     * case these are Strings, each containing one letter of the alphabet.
31     * They could be more complex objects that indicate the grouping for the adapter's
32     * consumption. The list view will call toString() on the objects to get the
33     * preview letter to display while scrolling.
34     * @return the array of objects that indicate the different sections of the list.
35     */
36    Object[] getSections();
37
38    /**
39     * Provides the starting index in the list for a given section.
40     * @param section the index of the section to jump to.
41     * @return the starting position of that section. If the section is out of bounds, the
42     * position must be clipped to fall within the size of the list.
43     */
44    int getPositionForSection(int section);
45
46    /**
47     * This is a reverse mapping to fetch the section index for a given position
48     * in the list.
49     * @param position the position for which to return the section
50     * @return the section index. If the position is out of bounds, the section index
51     * must be clipped to fall within the size of the section array.
52     */
53    int getSectionForPosition(int position);
54}
55