1 /*
2  * Copyright (C) 2015 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 
17 package com.android.deskclock.widget;
18 
19 import android.content.Context;
20 import android.support.v4.view.ViewPager;
21 import android.text.TextUtils;
22 import android.util.AttributeSet;
23 import android.view.View;
24 
25 import java.util.Locale;
26 
27 /**
28  * A {@link ViewPager} that's aware of RTL changes when used with FragmentPagerAdapter.
29  */
30 public final class RtlViewPager extends ViewPager {
31 
32     /**
33      * Callback interface for responding to changing state of the selected page.
34      * Positions supplied will always be the logical position in the adapter -
35      * that is, the 0 index corresponds to the left-most page in LTR and the
36      * right-most page in RTL.
37      */
38     private OnPageChangeListener mListener;
39 
RtlViewPager(Context context)40     public RtlViewPager(Context context) {
41         this(context, null /* attrs */);
42     }
43 
RtlViewPager(Context context, AttributeSet attrs)44     public RtlViewPager(Context context, AttributeSet attrs) {
45         super(context, attrs);
46         addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
47             @Override
48             public void onPageScrolled(int position, float offset, int offsetPixels) {
49                 // Do nothing
50             }
51 
52             @Override
53             public void onPageSelected(int position) {
54                 if (mListener != null) {
55                     mListener.onPageSelected(getRtlAwareIndex(position));
56                 }
57             }
58 
59             @Override
60             public void onPageScrollStateChanged(int state) {
61                 // Do nothing
62             }
63         });
64     }
65 
66     @Override
getCurrentItem()67     public int getCurrentItem() {
68         return getRtlAwareIndex(super.getCurrentItem());
69     }
70 
71     @Override
setCurrentItem(int item)72     public void setCurrentItem(int item) {
73         super.setCurrentItem(getRtlAwareIndex(item));
74     }
75 
76     @Override
setOnPageChangeListener(OnPageChangeListener unused)77     public void setOnPageChangeListener(OnPageChangeListener unused) {
78         throw new UnsupportedOperationException("Use setOnRTLPageChangeListener instead");
79     }
80 
81     /**
82      * Get a "RTL friendly" index. If the locale is LTR, the index is returned as is.
83      * Otherwise it's transformed so view pager can render views using the new index for RTL. For
84      * example, the second view will be rendered to the left of first view.
85      *
86      * @param index The logical index.
87      */
getRtlAwareIndex(int index)88     public int getRtlAwareIndex(int index) {
89         if (TextUtils.getLayoutDirectionFromLocale(Locale.getDefault()) ==
90                 View.LAYOUT_DIRECTION_RTL) {
91             return getAdapter().getCount() - index - 1;
92         }
93         return index;
94     }
95 
96     /**
97      * Sets a {@link OnPageChangeListener}. The listener will be called when a page is selected.
98      */
setOnRTLPageChangeListener(OnPageChangeListener listener)99     public void setOnRTLPageChangeListener(OnPageChangeListener listener) {
100         mListener = listener;
101     }
102 }
103