1 /*
2  * Copyright (C) 2014 Google Inc.
3  * Licensed to The Android Open Source Project.
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * You may obtain a copy of the License at
8  *
9  *      http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  */
17 
18 package com.android.mail.ui;
19 
20 import android.support.v4.view.ViewPager;
21 
22 import com.android.mail.utils.ViewUtils;
23 
24 /**
25  * Helper class for adding RTL support to a ViewPager. Note that this also requires a PagerAdapter
26  * that returns the pages in reversed order in the RTL case.
27  */
28 public class BidiViewPagerHelper {
29     private ViewPager mViewPager;
30 
BidiViewPagerHelper(ViewPager viewPager)31     public BidiViewPagerHelper(ViewPager viewPager) {
32         mViewPager = viewPager;
33     }
34 
getFirstPage()35     public int getFirstPage() {
36         return getIndexFromBidiIndex(0);
37     }
38 
getLastPage()39     public int getLastPage() {
40         return getIndexFromBidiIndex(mViewPager.getAdapter().getCount() - 1);
41     }
42 
getPreviousPage()43     public int getPreviousPage() {
44         return clampToBounds(getIndexFromBidiIndex(getBidiIndex(mViewPager.getCurrentItem()) - 1));
45     }
46 
getNextPage()47     public int getNextPage() {
48         return clampToBounds(getIndexFromBidiIndex(getBidiIndex(mViewPager.getCurrentItem()) + 1));
49     }
50 
clampToBounds(int position)51     private int clampToBounds(int position) {
52         return Math.max(0, Math.min(mViewPager.getAdapter().getCount() - 1, position));
53     }
54 
getBidiIndex(int position)55     private int getBidiIndex(int position) {
56         if (ViewUtils.isViewRtl(mViewPager)) {
57             return mViewPager.getAdapter().getCount() - 1 - position;
58         } else {
59             return position;
60         }
61     }
62 
63     /** Inverse of {@link #getBidiIndex} function. */
getIndexFromBidiIndex(int position)64     private int getIndexFromBidiIndex(int position) {
65         // getBidiIndex is equal to its inverse function so we are just calling getBidiIndex.
66         return getBidiIndex(position);
67     }
68 }
69